Vitamins, minerals and diet
- What are vitamins?
- What vitamins do?
- Where does the word vitamin come from?
- How were vitamins discovered?
- How many vitamins are there?
- How do vitamins and minerals work?
- What are the functions of macronutrients?
- How much of each vitamin and mineral do we need?
- What about Recommended Dietary Allowances?
- The state of optimum health
- Is it possible to get enough vitamins and minerals from food?
- The basics of a healthy diet
- How does food preparation affect vitamins and minerals?
- What about enriched and fortified foods?
- How good is the average diet?
- How common are nutrient deficiencies?
- What are the signs of marginal nutrient deficiencies?
- Can cravings be a sign of vitamin or mineral deficiencies?
- Are there tests for vitamin and mineral deficiencies?
- Are vitamin and mineral supplements necessary?
- Who takes supplements?
- Where do the vitamins in supplements come from?
- What types of supplements are available?
- Supplement labeling
- Types of supplements
- General guidelines for buying and taking supplements
- Supplements are no substitute for a balanced diet
- When should you take supplements?
- Can large doses of vitamins be harmful?
- Are large doses of vitamins beneficial for certain conditions?
- Clinical trials
- How reliable are scientific studies reported in the news?
What are vitamins?
Vitamins are substances which, in small amounts, are necessary to sustain life. They must be obtained from food as they are either not made in the body at all, or are not made in sufficient quantities for growth, vitality and well-being. Lack of a particular vitamin or mineral can lead to incomplete metabolism, fatigue and other health problems; and in severe cases, to deficiency disease. A deficiency of a particular vitamin causes disease symptoms which can only be cured by that vitamin.
Vitamins are chemically unrelated substances and all are organic. Organic substances are those that contain carbon and come from materials that are living, such as plants and animals, or that were once living, for example petroleum or coal. It is impossible to sustain life without all the essential vitamins.
What vitamins do?
Vitamins have many functions and influence the health of nearly every organ in the body. Their combination with other substances such as minerals, proteins and enzymes brings about certain chemical reactions. Individual vitamins have specific functions which vary widely and can overlap. They are involved in growth, the ability to produce healthy offspring and the maintenance of health. They play a role in metabolism, enabling the body to use other essential nutrients such as carbohydrates, fats, proteins and minerals. Vitamins are important for a normal appetite, in digestion, mental alertness and resistance to bacterial infections.
In addition to their basic roles in metabolism, some vitamins have specific preventive and therapeutic effects when taken in larger amounts. For example, niacin can be used to lower cholesterol and vitamin B6 can be used to treat premenstrual syndrome. Large doses of vitamins may slow, or even reverse many diseases previously thought an inevitable part of aging; such as cancer, heart disease, osteoporosis, impaired immunity, nerve degeneration and other chronic health problems. Many experts consider that taking larger doses of some vitamins is necessary for optimum health.
Vitamins are not substitutes for food. They cannot be assimilated without taking in food. They have no energy value of their own and are not components of body structures.
Where does the word vitamin come from?
In 1912, a Polish biochemist called Casimir Funk suggested that disease might be caused by a lack of something in the diet and cured by adding it. He thought this substance was necessary for life (vita) and contained nitrogen (amine) thus 'vitamine'. Later research showed that few of these substances contained nitrogen so the final 'e' was dropped giving us the word 'vitamin'.
How were vitamins discovered?
Diseases such as scurvy, rickets and pellagra have been known for centuries. It is only this century that the vitamins necessary for preventing them have been identified and isolated. Vitamins were originally discovered through animal experiments. Scientists fed animals diets known to cause certain diseases in man and then treated those animals with the nutrient missing from the diet. If the nutrient was found to cure or prevent the disease, it was identified as a vitamin.
How many vitamins are there?
In the USA the following are officially listed as vitamins: vitamin A; vitamin C; vitamin D; vitamin E; vitamin K; and the B vitamin complex containing: vitamin B1 (thiamin), vitamin B2 (riboflavin), vitamin B3 (niacin), vitamin B6 (pyridoxine), folic acid, vitamin B12 (cobalamin), biotin and pantothenic acid.
There are other substances whose vitamin status has not been established. Some researchers consider these to be vitamins but this is not generally accepted. Such substances include choline, inositol, para-aminobenzoic acid (PABA) and coenzyme Q10.
Vitamins are usually divided into two categories: fat soluble and water soluble. Vitamins A, D, E and K are fat soluble. They require an adequate supply of minerals and fats to be absorbed in the digestive system and are stored in the liver. The remaining vitamins are water soluble with any excess being excreted in the urine. These need to be replenished frequently.
How do vitamins and minerals work?
In order to be effective, vitamins and minerals work with the other nutrients found in food. They are known as micronutrients because they are required in very small quantities. Macronutrients, which include oxygen, water, carbohydrates, proteins and fats are needed in large quantities.
What are the functions of macronutrients?
Macronutrients provide energy and help maintain and repair the body.
Oxygen
Cells burn fuel for energy by combining it with oxygen.
Water
Your cells and organs depend on the involvement of water in all body processes, including digestion, absorption, circulation and excretion. Water surrounds and fills cells and tissues, forms the basis of body fluids, acts as a lubricant, transports oxygen and nutrients, keeps food moving through your gut, helps to regulate your body temperature and keeps your skin moist. Without food you could probably survive for several weeks; without water you would die in a few days.
Water makes up around 60 per cent of body weight and the average person needs two to three quarts (liters) of water per day to replace what is lost through the skin, urine, bowels and lungs. You obtain water from food, as a by-product of metabolism, and from drinking. Making sure you drink enough water is vital to maintaining good health. Many people do not drink enough.
Protein
Proteins are organic molecules containing carbon, oxygen, hydrogen, nitrogen and in some cases, sulfur.
They are made of linked chains of smaller molecules known as amino acids. These amino acids can combine in an infinite number of ways, and thousands of different proteins have been identified. Each protein has a unique sequence of amino acids which gives it a specific structure, shape and chemical characteristics.
The proteins in your body are made up of 20 main naturally occurring amino acids and some other minor ones. Some of these amino acids are essential constituents of your diet as your body cannot make them, whereas others are nonessential as your body can make them. Some amino acids can be considered semi-essential as they are only essential in your diet at certain times in your life, such as during childhood and in high growth demand states such as pregnancy. The essential amino acids are tryptophan, lysine, methionine, phenylalanine, threonine, valine, leucine and isoleucine. Arginine and histidine are considered semi-essential. The nonessential amino acids are tyrosine, glycine, serine, glutamic acid, aspartic acid, taurine, cystine, proline, and alanine.Proteins are involved in growth, repair and maintenance of body tissues. Enzymes are protein molecules which act as catalysts to stimulate biochemical reactions. There are literally thousands of different enzymes within a single cell that have many functions including the breaking down, joining together or separation of a wide variety of substances. Many hormones are proteins, including insulin, which regulates your blood sugar levels; and thyroid hormone, which controls your metabolic rate. Proteins also play a vital role in the functioning of your immune system, help to keep the correct amount of water in the cells, help to normalize the acid-base balance by acting as buffers, and can also be used as a source of energy for your body. One gram of protein provides 4 calories (17 kJ) of energy.
Carbohydrates
Carbohydrates are organic molecules which contain the elements carbon (C), hydrogen (H), and oxygen (O) in a ratio of 1:2:1. They come in several different types; including simple carbohydrates such as glucose, sucrose and fructose, which are found in refined sugar, fruits and honey; and complex carbohydrates, which are mainly starches and are found in grains, legumes and vegetables. Fiber is also a carbohydrate. Glucose is the end product of most carbohydrate metabolism in the body. The most important function of dietary carbohydrates is to provide you with energy for all your body functions, including heat production and muscle exertion. Glucose is converted to carbon dioxide and water and energy is released. Each gram of carbohydrate releases four calories of energy for use by the body. Carbohydrates also help in the digestion and assimilation of foods and in the regulation of protein and fat metabolism.
Glucose is the most common source of energy in the body and is particularly important for the brain and red cells as it is the sole source of energy for these body structures. Glucose is important in pregnancy for the formation of structural carbohydrates and lactose for lactation. Excess glucose is stored in the liver and muscles as glycogen, and when these reserves are filled to capacity, excess glucose is converted to, and stored as, fat.
Some carbohydrates cannot be digested by your body. These include cellulose, which therefore acts as a dietary fiber. Eating plenty of fiber helps to move food through your intestines, which contributes to the elimination of waste products.
Fats
Fats, which are also known as lipids, are compounds that are not soluble in water but are soluble in organic solvents. Like carbohydrates, they contain carbon, hydrogen and oxygen; and some contain nitrogen and phosphorus. The main type of dietary fat is triglycerides; others include phospholipids such as lecithin, and sterols such as cholesterol.
Fats have several vital functions including protecting internal organs from damage, providing insulation, helping to regulate body temperature, and transporting fat soluble substances such as vitamins A, D, E and K. Fats are also a source of energy. One gram of fat provides 9 calories (38 kJ) of energy after absorption. Fats also add flavor to food and help you feel full.
Fats are part of every cell membrane, organ and tissue. The type of fat you eat influences the characteristics of your cell membranes and organs, keeping them healthy or making them susceptible to disease. Fats are also important for the function of the nervous system and are involved in the manufacture of hormones and hormone-like compounds known as prostaglandins.
There are several different types of fats, which affect your health in varying ways. These include saturated, polyunsaturated and monounsaturated fats. All fats contain a mixture of these three types of fat, and one type predominates in a particular food.
Fats that are solid at room temperature are mostly saturated fat. Animal products, such as beef, pork, poultry, whole milk, cheese, sour cream, and yoghurt, as well as coconut, palm and palm kernel oils, contain mostly saturated fats. These fats can increase blood cholesterol levels and therefore raise the risk of heart disease. Eating foods high in saturated fats can also increase the risk of some cancers, including bowel cancer. Trans fats are produced from polyunsaturated fats, typically in margarine manufacture. Due to their adverse effects on health, they are usually grouped with saturated fats.
Fats and oils that are liquid at room temperature are mostly unsaturated, either monounsaturated or polyunsaturated. Canola, olive, and peanut oils are high in monounsaturated fats while corn, soybean, and sunflower oils are high in polyunsaturated fats. Two polyunsaturated fats are necessary for healthy body function. These are the essential fatty acids, linoleic and alpha linolenic acid.
For a few years, people were advised to eat polyunsaturated fats because they lower total blood cholesterol. However it is now known that polyunsaturated fats are susceptible to damage by free radicals and lower levels of beneficial HDL cholesterol. This increases damage to tissues and also the build-up of atherosclerotic plaque in the arteries. High intake of polyunsaturated fats has also been linked to cancer.
Monounsaturated fats can also help to lower levels of harmful LDL cholesterol and raise levels of beneficial HDL cholesterol. As they are less susceptible to oxidation, they do not increase the risk of disease. People who live in countries where the most commonly used type of fat is olive oil tend to have lower risk of diseases such as heart disease and cancer.
How much of each vitamin and mineral do we need?
For every person who asks this question, the answer will be slightly different. Each one of us has different needs and different ways of meeting those needs – a unique combination of stress and biochemical individuality. Genetic factors play an important part in this. For example, recent research indicates that as many as 5 to 15 per cent of people may have a particular type of genetic mutation in the DNA which codes for an enzyme involved in the metabolism of an amino acid known as homocysteine. This leads to higher homocysteine concentrations and therefore an increased risk of heart disease, and in women, of having babies with neural tube defects. Because folate and other B vitamins are involved in homocysteine metabolism, such people have higher folate requirements than those who do not have this type of genetic mutation, and may need supplements. Future research may show the presence of other common genetic variations, which throws doubt on the concept of assuming normality for nutrient requirements in any population.
Lifestyle factors also play a part. Someone who smokes or has a history of illness will have greater vitamin and mineral needs than someone who does not. The nutrient needs of an Olympic athlete are different to those of someone who sits on the couch and watches TV all day. Needs also vary according to sex, age and specific life events; a pregnant woman needs more iron than an elderly woman. Stress, disease, prescription drugs, environmental factors and intense physical activity can also raise requirements.
People vary in their ability to absorb and metabolize different nutrients. One person's genetic make up may mean they get enough vitamin C from an average diet whereas another would benefit from taking a supplement. The amounts and types of food people eat and the way they cook also affects the ability to obtain enough nutritional value from food.
What about Recommended Dietary Allowances?
In an effort to answer the question of how much people should aim to eat of the major nutrients, recommended dietary allowances (RDAs) were established by the Food and Nutrition Board of the US National Academy of Sciences National Research Council. RDAs were originally developed in the 1940s for food production in the military, and since their publication in 1943, they have been recognized as the most authoritative source of information on nutrient levels for healthy people. They are regularly updated, and since publication of the 10th edition in 1989, there has been an enormous amount of new research on the impact of nutrition on chronic disease.
In order to try and take this research into account, the expert panel responsible for setting the RDAs has reviewed and revised its approach and have published a new set of guidelines known as the Dietary References Intakes (DRI).
This new series of references includes what is known about how the nutrient functions in the human body; which factors may affect how it works; and how the nutrient may be related to chronic disease. Scientific research on nutrient metabolism and data on intakes in the US population, are used to set intakes for each age group, from babies to elderly people. Recommendations for pregnancy, lactation and maximum intake are also made.
The DRI provides sets of measures for each nutrient. The first of these is the Estimated Average Requirement (EAR), the intake value that is estimated to meet the requirement in 50 per cent of people in a specific group, usually defined by age and sex. At this level of intake, the remaining 50 per cent of the group would not have its needs met. The Recommended Dietary Allowance (RDA) is the dietary intake level that is sufficient to meet the nutrient requirements of nearly all the people in the group. These values refer to average daily intake over one or more weeks. The Tolerable Upper Intake Level (UL) is the upper limit of intake associated with a low risk of adverse effects in most people. It applies to long-term daily use.
For some essential vitamins and minerals, there is not enough information to come up with RDAs; and even for those nutrients for which they have been established, the lack of enough basic data means that they may be less accurate than they ideally should be. Where the experts consider that there is not enough evidence to come up with RDAs, they have established adequate intake (AI) values. DRIs have been published for the B vitamins, calcium, phosphorus, vitamin D, fluoride and magnesium. Others will follow in the near future. RDAs are designed for those of average height, weight, nutrient absorption ability and stress levels; and those who do not fit into those categories may need more. RDAs contain a margin of safety to make allowances for individual differences in absorption and metabolism. The RDA can be used as a goal for planning individual dietary intake. It is not intended to be used for assessing the diets of either individuals or groups or for planning diets for groups. The EAR may be more suitable for that purpose.
A separate set of recommendations called Reference Daily Intakes (RDIs) (previously known as the US RDAs) has been developed by the Food and Drug Administration (FDA). These do not vary with age or gender, but take the highest recommended dietary allowance value. On food labels you may see these referred to as Daily Values (DVs), listed for people who eat 2000 to 2500 calories each day.
Other countries use slightly different terms to refer to the RDAs. In Australia, the term Recommended Dietary Intakes (RDI) is used and in the UK, Recommended Nutrient Intakes (RNI).
UK, Recommended Nutrient Intakes (RNI). The RDIs set by the FDA are:
| Vitamin A | 5,000 iu |
| Vitamin C | 60 mg |
| Vitamin D | 400 IU |
| Vitamin E | 30 IU |
| Vitamin K | 80 mcg |
| Thiamin (B-1) | 1.5 mg |
| Riboflavin (B-2) | 1.7 mg |
| Niacin (B-3) | 20 mg |
| Vitamin (B-6) | 2 mg |
| Folate | 400 mcg |
| Vitamin B-12 | 6 mcg |
| Biotin | 300 mcg |
| Pantothenic Acid (B-5) | 10 mg |
| Calcium | 1,000 mg |
| Magnesium | 400 mg |
| Phosphorous | 1,000 mg |
| Chloride | 3,400 mg |
| Chromium | 120 mcg |
| Copper | 2 mg |
| Iodine | 150 mcg |
| Iron | 18 mg |
| Manganese | 2 mg |
| Molybdenum | 75 mcg |
| Selenium | 70 mcg |
| Zinc | 15 mg |
RDAs can be used as a basis for planning daily intakes. Many nutritionists advise aiming for 100 per cent of the RDA for all nutrients including vitamins and minerals. Greater intakes of vitamin C, beta carotene (which the body can convert to vitamin A) and vitamin E might be beneficial; but intakes of vitamins and minerals which may be toxic in large doses, such as vitamin A and vitamin D, should be limited to no more than 300 per cent of the RDA.
RDAs are calculated to meet the needs of healthy people, rather than the needs of those who are ill, stressed, taking medications or living in environments which cause nutrient requirements to be raised. They are also designed for people who are not particularly active, and those who exercise a lot may have greater needs. In recognition of the fact that older people usually require much higher levels of nutrients than those covered by the old RDAs, the new DRIs are, in some cases, higher for older people.
The state of optimum health
The answer to the question of how much of each vitamin and mineral a person needs also depends on how healthy a person wants to be. Health can be looked at as a variable state which ranges from severe illness to optimum health. It may be that a person feels healthy, but increasing the intake of vitamins and minerals could improve fitness, mental alertness and recovery time from injury. That person would then move further towards the state of optimum health.
An increasing amount of research suggests that for certain nutrients, particularly the antioxidant vitamins and minerals, the RDA level may not be enough to protect against some of the most prevalent diseases in developed countries, including cancer and heart disease.
While it is not possible to make accurate recommendations for the intakes necessary for optimum health, there has been a large amount of research into this issue. The following recommendations are made on the basis of studies which have looked at the therapeutic effects of vitamins and minerals.
Recommended dietary allowances and suggested optimal intakes
| Men | Women | Suggested intake | |
|---|---|---|---|
| Vitamin A | 1000 mcg RE | 800 mcg RE | 1500 mcg RE |
| Beta carotene | 10 to 30 mg | ||
| Thiamin | 1.2 mg | 1.1 mg | 5 to 10 mg |
| Riboflavin | 1.3 mg | 1.1 mg | 5 to 10 mg |
| Niacin | 16 mg | 14mg | 10 to 100 mg |
| Vitamin B6 (under 50) | 1.3 mg | 1.3 mg | 2 to 50 mg |
| Vitamin B6 (over 50) | 1.7 mg | 1.5 mg | |
| Vitamin B12 | 2.4 mg | 2.4 mg | 11 to 100 mg |
| Pantothenic acid | 5 mg | 5 mg | 10 mg |
| Biotin | 30 mcg | 30 mcg | 30 to 300 mcg |
| Folic acid | 400 mcg | 400 mcg | 400 mcg |
| Vitamin C | 60 mg | 60 mg | 100 to 1000 mg |
| Vitamin D (under 50) | 200 IU | 200 IU | 100 to 600 IU |
| Vitamin D (over 50) | 400 IU | 400 IU | |
| Vitamin D (over 70) | 600 IU | 600 IU | |
| Vitamin E | 10 mg alpha TE | 8 mg alpha TE | 67 to 500 mg alpha TE |
| Vitamin K | 80 mcg | 65 mcg | 60 to 300 mcg |
| Boron | 2 to 7 mg | ||
| Calcium (under 50) | 1000 mg | 1000 mg | 1200 to 1500 mg |
| Calcium (over 50) | 1200 mg | 1200 mg | |
| Chromium | 20 to 200 mcg | 20 to 200 mcg | 200 to 400 mcg |
| Copper | 1.5 to 3 mg | 1.5 to 3 mg | 3 mg |
| Fluoride | 3.8 mg | 3.1 mg | |
| Iodine | 150 mcg | 150 mcg | 200 mcg |
| Iron | 10 mg | 15 mg | 15 to 30 mg |
| Magnesium | 420 mg | 320 mg | 350 to 500 mg |
| Manganese | 2 to 5 mg | 2 to 5 mg | 10 mg |
| Molybdenum | 75 to 250 mcg | 75 to 250 mcg | 250 mcg |
| Phosphorus | 700 mg | 700 mg | 700 mg |
| Potassium | 2000 mg | 2000 mg | 2000 to 5000 mg |
| Selenium | 70 mcg | 55 mcg | 100 to 200 mcg |
| Vanadium | 10 to 60 mcg | 10 to 60 mcg | 50 to 100 mcg |
| Zinc | 15 mg | 12 mg | 15 to 30 mg |
Is it possible to get enough vitamins and minerals from food?
People living in Western cultures usually have all the nutritional advantages and disadvantages of an affluent lifestyle. By choosing the right types and amounts of food from the wide range of fresh, processed, mixed or pre-prepared food available, it should be possible for the average person to meet the RDAs for vitamins and minerals. However, the food available in Western cultures provides more fats, sugars, sodium and alcohol than is consistent with a healthy diet.
Many, although by no means all, nutrition experts agree that a balanced diet can supply all the vitamins and minerals that a healthy person needs. This line is most often taken by government organizations such as the American Dietitians Association and the American Heart Association. However, this view may be changing. In the light of recent research on folate and the prevention of neural tube defects, Godfrey Oakley, MD of the Centers for Disease Control in Atlanta, commented in an editorial in the New England Journal of Medicine, that "anyone who chooses to counsel a woman to consume 400 mcg of food-derived folate rather than 400 mcg of supplemental folic acid will be recommending a strategy that has not been proved to prevent birth defects and that leads to lower blood folate concentrations."
Leaving aside the fact that opinions differ as to exactly what constitutes a balanced diet, not everyone is able to, or wants to, eat such a diet all the time. Individual vitamin and mineral requirements may vary as much as 200-fold due to differences in genetic make up, lifestyle, physical and emotional stress, and other factors. Some people are able to meet their nutritional requirements with an average diet and no supplements, while others have needs which are greater than their diet can meet.
The issue of the quality of the food we eat is also relevant. Modern methods of food production and manufacturing can adversely affect the nutritional value of food. Soil quality has been lowered through farming methods and the use of fertilizers. Many chemicals are added to food during the growing and processing stages and several of these, including pesticides, can accumulate in the body and have toxic effects. Fruit and vegetables are often picked before they are ripe, in some cases before they have developed their full content of vitamins and minerals. When food is stored for later use, some of the content may decay during storage. Processing of foods removes many valuable nutrients, and a person whose diet is high in these foods may be at risk of nutrient deficiencies.
The basics of a healthy diet
Ideas about what comprises healthy eating behaviour vary from one culture to another. For several generations, America has been a meat and milk country with the daily consumption of dairy products and beef seen as a healthy luxury. However, growing evidence suggests that the typical American diet is too high in protein, fat and salt and too low in fruit, vegetables and complex carbohydrates.
People choose to eat foods for many reasons, not just for their nutritional value. Habit, tradition, economy, convenience, availability, emotional comfort, religious beliefs and environmental concerns play an important part in food choices. It seems that there is no right way for everybody to eat. However, there are some general guidelines to help you eat a healthy diet. It is important to remember that it is the food eaten over a number of days which is important rather than individual meals or days. This allows more flexibility in choosing foods, and fits the theme of consuming a variety of foods with room for the occasional treat.
- Eat a wide variety of different types of foods. This ensures you get all the nutrients you need and limits your intake of the ones which may cause you harm. Eating fresh foods, preferably simple ones that are in season, is vital to make the most of what your food has to offer. Processed and prepared foods should be avoided as much as possible, as they are often high in sugar, salt, fat and additives.
- Try to eat plenty of different types of fruit and vegetables, particularly greens and those that are brightly coloured. They should be raw or lightly cooked and should not be coated in fatty dressings or cream sauces. If possible, eat organic to minimise consumption of pesticides.
- Legumes and whole grains should be regularly included in your diet . They are great sources of carbohydrate, and they contain healthy levels of protein and many other beneficial substances.
- Complex carbohydrates should account for around 40 to 50 per cent of total calories consumed; more if you exercise a lot. Whole grain products are better than refined ones because they still contain the vitamins and minerals lost in the refining process.
- Try to limit your sugar intake, particularly if you suffer mood swings, depression and fluctuating energy levels. If you do eat sugar, try not to combine it with fat, particularly if you are trying to lose weight.
- The latest research on fat suggests that it is not just how much you eat but what type that increases the risk of obesity and disease. Try to cut down on foods high in saturated fat such as meat, whole milk, butter, palm oil and coconut oil. Polyunsaturated fats found in margarine and some vegetable oils are linked to an increased risk of cancer, autoimmune diseases and lowered immunity. Replace these fats with olive oil, preferably extra virgin or virgin. It is consistently associated with lower disease levels. Beneficial omega-3 fatty acids are found in oily fish and oils such as flaxseed oil, and these should be included in your diet as often as possible.
- Limit your protein intake. A 110 g serving of meat, chicken, fish or tofu once a day is likely to be enough unless you are pregnant, breastfeeding or ill. Too much protein may contribute to fatigue, lowered immunity, lack of energy and liver and kidney problems. It also leaches minerals such as calcium out of your body, and increases the risk of osteoporosis.
- Limit intake of dairy products as they can aggravate mucus production and lower immunity.
- Limit salt intake, particularly if you are salt-sensitive.
- How your body processes the food you eat is as important as the food you put into it. Try to eat with full attention and chew your food properly. Eating with care and attention helps your body to digest food more efficiently than if you eat when you are angry or stressed. And last but by no means least, learn to trust your body and understand its needs and signals. Eating should be a pleasurable experience and eating foods you don't like because you think they are good for you is not listening to your body.
- Drink alcohol in moderation if at all. Children, adolescents and pregnant women should not drink alcohol.
How does food preparation affect vitamins and minerals?
The way food is prepared also affects its nutritional value. For example, fried chicken contains twice the calories of grilled chicken but the same amount of protein, vitamins and minerals. The way food is stored and cooked affects the vitamin and mineral content. Some vitamins are easily affected by exposure to light, heat and air.
- Vitamins A, D, E and K, riboflavin and beta carotene are destroyed when exposed to light.
- Vitamins C, A, B12, folic acid and thiamin are destroyed by heat.
- Vitamins C, A, D, E, K, B12 and folic acid are destroyed by exposure to air.
- Vitamins C, B6, thiamin, riboflavin, niacin, selenium, potassium and magnesium leach into cooking water.
- Vitamins C, B12, folic acid, thiamin and riboflavin are destroyed when combined with acid or alkaline substances.
To make the most of the vitamins and minerals in food, there are several guidelines to follow.
Food storage:
- Eat fruit and vegetables as fresh as possible.
- Store refrigerated foods at less than 40oF, frozen foods below 0oF and canned and dry food in a cool, dry place.
- Store canned and frozen food for no longer than the use by date.
- Store grains, flour and dried beans and peas in dark containers or in the refrigerator.
Food preparation:
- Cook food in a minimal amount of water for the shortest possible time. Vegetables should be just tender rather than soggy and overcooked. Frozen vegetables should be cooked without thawing and fresh vegetables should be chopped just before cooking or serving.
- Use low to moderate heat when cooking meat, eggs and milk.
- Use the leftover liquid for sauces, stews or juices.
What about enriched and fortified foods?
Adding vitamins and minerals to certain foods is common practice in developed countries. Enrichment involves putting back nutrients lost during processing, while a fortified food will have a nutrient added to levels not present in its natural state. For example, flour is usually enriched with thiamin, riboflavin and niacin, and milk is fortified with vitamin D. Since January 1998, commercial grain products in the USA have also been enriched with 140 mcg of folic acid per 100 g of grain product. It is estimated that this will deliver an average increase in intake of 100 mcg per day. Breakfast cereals may contain up to a daily dose of folic acid.
For many people, these foods are very important sources of vitamins and minerals and may be responsible for the low levels of deficiency diseases seen today. However, enriched foods often contain much lower levels of nutrients than those which are present in the unprocessed versions. For example, almost all the B vitamins are removed from the cereals and grains used in baking and only a few are put back synthetically during enriching. Eating a diet that includes, but is not limited to, enriched foods is one way to get essential nutrients.
When choosing foods, it is important to read the labels carefully as these contain information on the fat, sugar, salt and vitamin and mineral content of food. In general, the more processed a food is, the higher the salt, sugar and fat content and the lower the vitamin, mineral and fiber content.
How good is the average diet?
Surveys suggest that most people do not consume a balanced diet. Results of nutrition surveys show a large gap between the dietary guidelines and what people actually eat. The US National Health and Nutrition Examination Survey (NHANES II) shows that sugar intake makes up 25 per cent of total calories and fat intake approaches 34 per cent. This means that foods which have poor nutritional value make up over half the daily calories.
Other results show that:
- On any one day, an estimated 45 per cent of people don't consume any fruit or juice and 22 per cent don't eat any vegetables. Less than 10 per cent of people consume the recommended five or more servings of fruit and vegetables.
- Only a third of the population consumes foods from all the food groups on a typical day, with less than 3 per cent consuming foods from all food groups in at least the recommended amount.
- Many diets contain half the recommended amount of magnesium and folic acid; as many as 80 per cent of women who exercise may be iron-deficient; and the average calcium intake is 636 mg per day (two-thirds the RDA).
- Seventy-one per cent of males and 90 per cent of females consumed less than the 1980 recommended dietary allowance (RDA) of vitamin B6.
- The average calcium intake of teenage girls resembles that necessary for 3–5 year olds.
How common are nutrient deficiencies?
It is often difficult to link one vitamin with a particular disease except in severe cases where a deficiency results in well-documented physical symptoms. For example, bleeding gums are a sign of scurvy which is caused by lack of vitamin C, and goiter is caused by an iodine deficiency.
Nutrient deficiencies occur for several reasons; including inadequate intake, inadequate absorption, inadequate utilization, increased requirement, increased excretion and increased breakdown. Anyone in whom these situations are found is at risk of deficiency. In developed countries, where the food supply is good, there are relatively few cases of severe deficiency. However, the statistics given above suggest that marginal deficiencies may be common.
Nutrient deficiencies can be classified into five stages:
- A preliminary deficiency.
- A biochemical deficiency where the nutrient concentration in the tissues becomes lower.
- A physiological stage where the critical body processes, such as enzymes and hormones that depend on the nutrient are slowly lost. The first three stages are sub-clinical or marginal stages.
- A clinical stage where the signs of the deficiency are obvious and can be detected by the eye.
- An anatomical stage which can lead to death.
Marginal deficiency symptoms are nonspecific and can often go unnoticed or be attributed to other causes. When combined with other factors such as disease, prescription drugs, stress, smoking and pollution, they can increase susceptibility to illness or lead to clinical deficiencies. It is possible that marginal nutrient deficiencies play a role in many of the diseases of old age such as osteoporosis, arthritis, heart disease and high blood pressure. Ensuring optimal intakes of vitamins and minerals is therefore vital for present and future health.
What are the signs of marginal nutrient deficiencies?
There are many signs of marginal nutrient deficiencies and these can often be similar for different nutrients. In many cases, the only signs of a marginal deficiency will be vague symptoms such as fatigue, lethargy, difficulty concentrating or just feeling that things are not quite right. Diagnosing marginal deficiencies is difficult as many laboratory tests are expensive and time- consuming, if they are available at all. Marginal deficiencies of single nutrients are rare as it is likely that a person whose diet is deficient in one vitamin or mineral is deficient in others too. Some marginal deficiency symptoms include:
- Bruising easily may be linked to vitamin C and K deficiency.
- High cholesterol may be due to antioxidant vitamin and B complex deficiencies.
- Reduced taste sensation may be due to zinc deficiency.
- Fatigue may be due to iron, vitamin B12, folic acid or iodine deficiency.
- High blood pressure may be due to potassium and calcium deficiencies.
- Muscle cramps and pains may be due to calcium and magnesium deficiencies.
- Osteoporosis may be linked to calcium deficiency.
There is increasing evidence to suggest that long-term marginal intake of certain nutrients can increase the risk of developing degenerative diseases such as cancer, diabetes and heart disease.
Can cravings be a sign of vitamin or mineral deficiencies?
It is possible that nutrient deficiencies may result in cravings for certain foods; for example, potassium deficiency might result in a craving for bananas or potatoes; calcium deficiency might result in a craving for cheese, milk; and B vitamin deficiency in a craving for nuts. There are, however, many other factors such as food allergies and hormonal influences which may play a role in food cravings. There is evidence to suggest that inadequate vitamins and minerals in the diet may result in cravings which cause people to fill up on foods that are high in calories and low in nutrients, causing the increasingly common problem of obesity.
Are there tests for vitamin and mineral deficiencies?
There are many tests for assessing vitamin and mineral status. They vary widely in availability, credibility and accuracy. A detailed medical history and physical examination can detect clinical vitamin and mineral deficiencies in more advanced stages. Such an examination would involve looking carefully at weight, height, the condition of skin, hair, fingernails, tongue, eyes and the mucous membranes inside the mouth and eyes.
Laboratory tests of blood, urine or tissues can detect vitamin or mineral deficiencies at an earlier stage than a physical examination. Blood levels of various enzymes are also indicators of nutritional status. However, many laboratory tests are too expensive and complicated to conduct on a routine basis.
There are many alternative tests to determine nutritional status. However, there is no proof that these tests can provide a complete analysis of a person's nutritional state. They may be useful in certain cases. Hair analysis, as a test for nutritional status, is considered unreliable as results can be affected by shampoo, dyes, tobacco smoke and other environmental factors. Hair growth can also slow down in malnourished people, increasing nutrient concentrations in hair while body stores drop. It can be a useful test for toxic metal concentrations.
Are vitamin and mineral supplements necessary?
Whether or not vitamin and mineral supplements are necessary is the most controversial topic in nutrition. The question of a need for supplements is central to the debate about the levels of vitamins and minerals required to promote optimal health. Given that people vary so much in their requirements and that very few people eat really well-balanced diets, vitamin and mineral supplements can be viewed as a relatively inexpensive form of 'nutritional insurance'. Increasing evidence suggests that the amounts of nutrients adequate to prevent deficiencies are not the same as those necessary for optimal health.
Who takes supplements?
Data from the second National Health and Nutrition Examination Survey (NHANES II) suggest that almost 35 per cent of Americans between 18 and 74 years of age take vitamin and mineral supplements regularly. Other surveys put the figure much higher. In 1988, Americans spent approximately $2-2.5 billion on vitamin and mineral supplements. The total amount spent on foods and pill supplements for health benefits was $6 billion. Nutritional supplements are big business and marketing hype often starts where the scientific evidence ends.
Those who use supplements tend to be older, have higher income and higher education levels. However, statistics also show that those with higher nutrient intakes are more likely to take vitamin supplements. This means that, in many cases, supplements are taken most often by those who need them least.
The most popular supplements are multivitamins, vitamin C, vitamin E, B complex, calcium and magnesium. Recent media coverage of the benefits of herbs such as Echinacea, St John's wort and Ginkgo means that these are also very popular. Women are more likely to use supplements than men, and most people who take them tend to do so because they feel that their food is of poor quality and contains toxic chemicals. Some people see supplements as health insurance and some take them for what they see as their specific benefits; for example, vitamin C for colds.
Who might need supplements?
Many people may benefit from a balanced vitamin and mineral supplement, including those who have irregular eating habits, skip meals, or eat large amounts of processed and refined foods. There are also certain groups of people who are at particular risk of nutrient deficiencies because of other lifestyle, environmental or disease factors. The following are some examples of those at risk.
- Older people often have higher nutrient needs than younger ones due to lower dietary intake, reduced absorption and metabolism, and illness. Lack of appetite, loss of taste and smell, and denture problems can all contribute to a poor diet. Older people who eat alone or are depressed may also not eat enough to get all the nutrients you need from food. Those age 65 or older are likely to need to increase intake of several nutrients, particularly vitamin B6, vitamin B12 and vitamin D because of reduced absorption. They may benefit from supplements (See page 454 for more information.) There's also evidence that a multivitamin may improve immune function and decrease the risk of infections in older people.
- Premenopausal women may benefit from iron supplements as their diets are often low in this mineral and iron deficiency anemia is relatively common. However, there is evidence that too much iron can increase the risk of heart disease in those who are susceptible, and certain people should avoid iron supplements (See page 258 for more information.)
- Postmenopausal women have high calcium needs (up to 1500 mg per day in those not taking hormone replacement therapy). This amount is not usually found in multivitamin supplements as it is too bulky and separate supplements may be useful (See page 197 for more information.) Higher vitamin D intake is also necessary.
- It is worth considering taking extra vitamin C, vitamin E and beta carotene as several studies show that these vitamins in large doses may help protect against aging-related disorders such as cancer, heart disease, diabetes and cataracts. This may be particularly important in those who have a family history of such diseases.
- Pregnant women are routinely prescribed folic acid supplements to prevent neural tube defects; and calcium, iron and zinc requirements also substantially increase. (See page 104 for more information.)
- Someone who is chronically ill has higher nutrient needs and may find vitamin and mineral supplements useful, particularly if they are taking long- term medications.
- Supplements may also be beneficial for those on weight loss diets. Many people, particularly women, eat low calorie diets which are inadequate in iron, calcium and zinc.
- If your diet has limited variety due to intolerance or allergy, you may benefit from a vitamin-mineral supplement.
- Diseases of the liver, gallbladder, intestine and pancreas, or digestive tract surgery, may interfere with normal digestion and absorption of nutrients. Anyone with one of these conditions may be advised to supplement with vitamins and minerals.
- Strict vegetarians who avoid meat and dairy products must obtain vitamin B12 from supplements. They may also benefit from extra iron, calcium and zinc (See page 448 for more information.)
- Those who smoke may benefit from vitamin C supplements. Smoking reduces vitamin C levels and causes production of harmful free radicals.
- Those who drink a large amount of alcohol may need supplements. Alcohol affects the absorption, metabolism and excretion of vitamins.
- Those under physical or emotional stress may also benefit from supplements.
Where do the vitamins in supplements come from?
Most vitamins are extracted from the food sources in which they naturally occur. For example, vitamin A is often extracted from fish liver oil. Vitamin B comes from yeast or liver, vitamin C from rose hips, and vitamin E from soybeans, wheatgerm or corn.
Supplements are available from many sources but most supplement manufacturers get the raw materials from the same small group of suppliers. They are then packaged and labeled before being sent to distributors or retail outlets.
What types of supplements are available?
There is a vast range of vitamin, mineral and other nutritional supplements available in supermarkets, health food stores and drugstores. Products vary widely in quality and effectiveness, and evidence to support some of the claims made by those who sell them is inconclusive at best.
Most supplement manufacturers follow good manufacturing practices, which ensure that the product contains what it says on the label; that it breaks down to a form which is available for absorption; and does not contain toxic chemicals. If in doubt, it is worth checking with the supplier. Good quality supplements are available from medical practitioners, health food stores, drugstores and supermarkets. Many experts recommend buying name brands or own brand supplements from large national stores with a reputation for quality.
Vitamin and mineral supplements come in various forms. The most common are tablets which are convenient to store and carry and have the longest shelf life. Capsules are also easy to store, but may not be as good at protecting the contents from oxidation. Enteric-coated capsules, which are also known as timed release supplements, are another form. They are designed to pass through the stomach to dissolve in the intestine. Fat soluble vitamins and other oil supplements often come in the form of gelatin capsules. Powder forms do not contain fillers, binders or additives. Liquids are suitable for people who have difficulty swallowing capsules.
Vitamin supplements contain many other substances such as fillers, binders, lubricants, disintegrators, colors, flavors and sweeteners, coating materials and drying agents. A person who is prone to allergies should check the ingredients of a particular type of supplement.
When buying supplements, it is helpful to have a clear idea of what nutrients are necessary, and in what amounts. This should be based on dietary strengths and weaknesses and particular needs. Reading the labels carefully should provide enough information to match the product with a person's individual needs.
Supplement labeling
The US government has recently announced new rules on the labeling of dietary supplements. The new rules are designed to give consumers more complete information regarding the ingredients in dietary supplements. They apply to vitamins, minerals, herbs and amino acids. The rules require the products to be labeled as dietary supplements and to carry a 'Supplement Facts' panel that lists how much of the RDI of nutrients are in the product. For ingredients that have no RDI, such as herbs, the package will list the ingredients. Herbal products must identify the part of the plant used to make the substance.
Supplements could only claim to be 'high potency' if a nutrient is present at 100 per cent or more of the RDI. For multivitamin supplements to carry the 'high potency' labeling, at least two-thirds of the nutrients must be present at levels that are more than 100 per cent of the RDI.
The term, antioxidant, may be used to describe a nutrient where scientific evidence shows that if it is absorbed in sufficient quantity, the nutrient (such as vitamin C) will inactivate free radicals or prevent free radical-initiated chemical reactions in the body.
The amounts of vitamins and minerals in supplements are indicated in a number of ways:
- A milligram (mg) is 1/1000th of a gram (g); there are 1000 mg in a gram.
- A microgram (abbreviated mcg or mg) is 1/1000th of a milligram; there are 1,000,000 micrograms in a gram.
- The international unit (IU) is an arbitrary measure used for vitamin A (and beta carotene), vitamin D and vitamin E.
- Retinol equivalents (RE) are now being used to measure vitamin A (and beta carotene activity) and tocopherol equivalents (TE) to measure vitamin E. This is because vitamins A and E are found in several different forms in the body and these measurement units make it possible to compare the various forms (See pages 39 and 163 for more information.)
Types of supplements
There are various types of supplements. Different preparations suit different people and it is a good idea to experiment with different types to find the best combination.
Water solubilized fat soluble vitamins
The oil soluble vitamins A, D, E and K are available in dry or water soluble form for people who cannot, or do not want to consume oil, for example acne sufferers or people with fat malabsorption disorders such as celiac disease.
Natural vs synthetic
In most cases, natural vitamins have not been shown to be more beneficial than synthetic vitamins. However, vitamin E seems to be the exception and the natural form of vitamin E, d-alpha tocopherol is more potent than the synthetic form, dl-alpha tocopherol. Sometimes vitamin supplements contain other compounds which may enhance the effectiveness of the vitamin, although this is a much debated issue. For example, natural vitamin C contains compounds known as bioflavonoids which, although they may or may not enhance absorption, possibly have anticancer properties of their own. Yeast grown on chromium and selenium- rich media form organic compounds which may be better absorbed by the body than inorganic salts.
Chelated minerals
Some minerals in supplements are combined with other compounds to make organic forms. This process is known as chelation and may make the minerals more digestible as it is similar to the form in which they occur in nature. For example, ferrous fumarate is a chelated form of iron. Chelated mineral supplements may be absorbed better than nonchelated minerals. Some people, particularly those who are older, often have low stomach acid; and minerals are often chelated with acidic compounds, for example calcium citrate. In some cases, chelated minerals may be less irritating to the stomach than nonchelated minerals.
Timed release supplements
Timed release or sustained release vitamins are designed to dissolve and be absorbed slowly. The theory behind this is that the vitamins have maximum effectiveness when blood levels are stable, and losses through excretion are minimal. However, some experts believe that timed release supplements are not necessarily better. It is possible that by the time some of these tablets have dissolved, they have passed the particular part of the intestine where they would be absorbed. High blood levels of some vitamins may also be useful in treating some conditions.
General guidelines for buying and taking supplements
- A well-balanced multivitamin supplement is usually better than several single supplements. Such supplements contain approximately 100 per cent to 300 per cent of the RDA for those vitamins and minerals which may have protective effects or are often lacking in the diets of many people. These include vitamins A (preferably in the form of beta carotene), E, C, thiamin, riboflavin, niacin, B6, folic acid, pantothenic acid, biotin, calcium, copper, iron, magnesium and zinc. However, many multivitamin and mineral supplements do not contain sufficient calcium or magnesium, and additional single supplements may be useful for those who need higher doses, such as postmenopausal women.
- Some supplements group vitamin A and beta carotene together, making it difficult to tell how much of each is present. A supplement which provides vitamin A as beta carotene only may be best. Most multivitamin supplements contain only small amounts of beta carotene so it may be worth taking a separate supplement; although probably not if you are a smoker.
- It may be beneficial to choose a supplement that provides minerals in the following amounts: chromium 50 to 200 mcg, manganese 2.5 to 5.0 mg, selenium 50 to 200 mcg. Amounts much higher than this may be toxic.
- Supplements which contain useless or potentially harmful substances should be avoided. Most experts feel that ingredients which have not been shown to be necessary in the diet may merely increase the price of a supplement. It is also best to avoid products which contain artificial flavor, preservatives and color.
- Expensive supplements are not necessarily better. It is more important to check the nutrient content of the supplement. Supplements with the same ingredients which are priced much lower than various reliable brands may not be high quality and those which are priced considerably higher may be too expensive.
- Avoid expensive supplements sold through multilevel marketing (MLM). These include multimineral and spray vitamins. There is almost no scientific evidence to support the claims that are often made, and the products are over-priced.
- Vitamins should be stored in a cool dry place away from direct sunlight in a closed container. If they are kept sealed, in these conditions they should last for two or three years. Once they are opened, they usually have a 12- month shelf life.
- If you are unsure whether the products you are buying will break down in your stomach in time to be absorbed, try dropping the tablet into a glass of vinegar. If it dissolves in 30 minutes it is likely you will be able to absorb the nutrients it contains.
Supplements are no substitute for a balanced diet
The most important thing to remember is that supplements are no substitute for a balanced diet. Even the best vitamin studies only show a partial reduction in the risk of disease. No supplement allows a person to smoke, drink a lot of alcohol, eat whatever they want and still stay healthy. There are many substances, other than vitamins and minerals, which play an essential role in protecting against disease and improving health. Many studies show that people whose diets are high in fruit and vegetables live longer. For example, eating broccoli, carrots and leafy green vegetables does appear to be more protective than taking beta carotene and vitamin C supplements. As well as being a good source of beta carotene and vitamin C, broccoli contains compounds known as indoles that may protect against certain forms of cancer. It is also high in fiber.
When should you take supplements?
Vitamins work with food so supplements should usually be taken with meals. This also helps to minimize the nausea, heartburn and other gastric disturbances that some supplements can cause if taken on an empty stomach. The digestive juices can help to break down supplements so they are better absorbed. Supplements can be easier to swallow if taken with thicker liquids such as juices. It may be better to take supplements in smaller doses several times per day.
Some experts feel that, if vitamins are taken once a day it should be after the largest meal, which is usually dinner. Others feel that the body is in the best state to absorb nutrients earlier in the day.
Some vitamins and minerals compete for absorption or antagonize each other. In these cases, it may be best to take the supplements at different times; although if a person is taking large doses of supplements, these interactions may not matter.
Can large doses of vitamins be harmful?
For the majority of people who take a daily multivitamin supplement with no more than 100 per cent of the RDA, the risks of side effects are probably small. However, high doses of some vitamins can have serious side effects.
Fat soluble vitamins stay in the body longer than water soluble ones, and there have been cases where large doses of vitamin A and vitamin D have had toxic effects. These cases are rare and symptoms disappear when the large doses are stopped. Research has suggested that temporary and even permanent damage can be caused by overdosing on B vitamins. People at risk of developing kidney stones should avoid large doses of vitamin C (see sections on individual vitamins for cautions).
Interactions between different nutrients are very complex. Minerals work in critical ratios to one another. Too high an intake of one mineral may result in a deficiency of another so minerals should be taken in one-to-one RDA ratios. For example, excessive zinc intakes can result in iron and copper losses, so if daily zinc intake is doubled from 15 mg to 30 mg, then daily iron intake should be doubled from 10 mg to 20 mg to maintain the ratio.
Are large doses of vitamins beneficial for certain conditions?
Megavitamin or megadose therapy is the use of vitamins and minerals in amounts greater than ten times the RDA. Vitamins exert their natural physiological functions by binding to compounds such as enzymes. The amount of a particular enzyme that a cell can make is limited, and when the vitamin has bound to all the available enzymes, it may not exert any greater physiological effect. Vitamins and minerals in doses larger than those needed for these effects exert pharmacological or drug-like effects. An example of this is the use of niacin at 40 times the RDA to lower cholesterol.
The use of vitamins and minerals in this way is relatively new and in most cases, extremely controversial. Many of these treatments are not accepted by mainstream medical doctors for the reason that there is a lot of ambiguity, incomplete information and hypothesis.
Orthomolecular medicine
Orthomolecular medicine is defined as “the preservation of good health and the treatment of disease by varying the concentrations of substances in the human body that are normally present and required for health.” This definition was given by the Nobel Prize winning chemist, Linus Pauling, who believed that many diseases can be treated or prevented by finding the optimal amounts of nutrients required for each person's health.
Orthomolecular medicine is concerned not only with maintaining optimal health but with the prevention and treatment of disease. Experiments using large doses of vitamins have included niacin therapy for schizophrenia, vitamin C for cancer and viral illnesses, and vitamin B6 for carpal tunnel syndrome. The results of these and other nutrition studies have generated a lot of media attention. One of the main criticisms of those who use orthomolecular medicine is that their research has little support from clinical trials.
Clinical trials
Much of the information we have about the effects of vitamins comes from clinical trials. A clinical trial is an experiment conducted with patients as subjects. The strongest experimental design is the randomized design in which subjects (patients) are randomly assigned to treatment groups. Some clinical trials compare treatment methods and others assess the affect of a particular treatment on prevention of disease.
Controlled trial
A controlled trial is a study in which researchers actively produce a treatment and deliberately assign people to the treatments.
Randomized trial
In a randomized clinical trial, there are two or more therapeutic treatment groups. One treatment may be a placebo control in which a biologically inert substance is used. Often, the 'control' condition is compared to experimental treatments.
Single-blind trial
A trial in which the treatment is given in such a way that the subject cannot tell what it is. This helps to minimize other effects of the treatment, such as the placebo effect.
Double-blind trial
A double-blind trial is a completely random design where there is one real treatment and a placebo. Not only are the subjects assigned to the two groups at random, but neither the subjects nor those administering the treatments knows which treatment a subject is getting.
Observational study
Researchers observe what happens but do not actively intervene with the assignment of people to treatment groups.
Crossover trial
A trial in which participants receive two or more treatments one after the other and act as their own controls for comparison of drug treatments.
Anecdotal evidence
Evidence based upon haphazard observations which come to attention because they are striking in some way.
Confounding factor
A factor that is not taken into account that gets mixed up with the treatment factors and has a marked effect on the response.
Bias
The favoring of certain outcomes not due to the treatments.
Epidemiological studies
The study of the occurrence, distribution and causes of disease in man.
Prospective cohort study
In this type of epidemiological study two groups (cohorts) of subjects are identified, one of which is exposed to a treatment, an environmental condition, or health risk factor, and the other group is not. The subjects are then followed over time and the effects assessed.
Case-control study
In an epidemiological case-control study a group of patients who already have a disease or other outcome (the cases) is compared to another group of controls who do not. These studies are done retrospectively.
Meta analysis
A systematic review of studies that pools the results of two or more studies to obtain the answer to an overall question of interest.
How reliable are scientific studies reported in the news?
Media reporting of nutritional issues can often add to the confusion that most people feel. Sometimes news stories about health seem to contradict one another, one says something is good for you, and another says that the same thing is bad for you. Conflicting medical reports can make even the most educated consumer confused about what to believe and what to do.
Nutrition stories regularly make headlines in newspapers and magazines and often seem credible because they claim to report 'scientific research.' Due to the pressure to report whatever is new, some stories get more media attention than they deserve and can become distorted in the process. News stories, particularly those on TV and radio, must often be condensed because of space limitations. It is worth analyzing the whole article to find out more about the research. Studies tend to carry more weight if they are done in large academic institutions, by well-qualified researchers and reported in reputable scientific journals which have been reviewed by other scientists. Studies done on humans rather than animals and on large groups of people are also more significant.
No single scientific study, however well done, can change the totality of evidence. There are many links in the process of drawing conclusions about the course of a disease and the ability of vitamins and minerals to affect it. A new study may move current thinking a little bit more in one direction than another, but a large number of studies from different places are necessary to understand a disease process. Science requires repeatable experiments. If a nutrient is useful, the effects will be seen time and again if the experiments are done properly.