Antioxidants
What is it?
The antioxidant vitamins are vitamin E, vitamin C, and the beta carotene form of vitamin A. Minerals such as selenium, copper, manganese and zinc also have antioxidant properties when combined with certain enzymes. There are many other antioxidant compounds in food, such as bioflavonoids found in fruit and vegetables; coenzyme Q10 found in fish, nuts and lean meats; and sulfur-containing amino acids.
Antioxidants and disease prevention
There is no research which shows that antioxidants definitely protect against, or cure any disease. However, growing evidence strongly suggests that they have the power to prevent diseases such as cancer, coronary heart disease and cataracts. Studies show that diets high in antioxidants or antioxidant supplements reduce cancer death rates, cold and flu infections and protect against atherosclerosis, heart disease and cataracts. These vitamins may improve immune system function and may even delay some of the effects of aging. This is probably due to their ability to intercept and extinguish free radicals.
Free radicals
Oxygen, the most critical nutrient for life, is the main source of free radicals, which could be the fundamental cause of many chronic diseases and even of the aging process. Free radicals are highly reactive oxygen fragments which are created by normal chemical processes in the cells. They lack electrons and try to steal them from other molecules to regain balance, a process known as oxidation. Free radicals include the superoxide radical, the hydroxyl radical and hydrogen peroxide.
A certain level of free radicals is essential for good health as they are involved in fighting infection and in the contraction of smooth muscles in the blood vessels. Cells have a number of ways of dealing with excess free radicals including the use of enzyme systems and specific antioxidants.
What antioxidants do
An antioxidant is a substance which gives up electrons easily so it can neutralize oxidants, including free radicals. Unfortunately, these protective systems may not always be adequate when the system becomes overloaded with free radicals.
When the antioxidant systems of the body are overwhelmed, free radicals stabilize themselves by stealing electrons from chemically stable compounds, often causing the generation of more free radicals which react further with other compounds, causing yet more damage. These split second chain reactions spread throughout the body, attacking vulnerable sites in the cells and causing damage that can result in chronic disease.
Free radicals can be produced in dangerous amounts by irritants such as cigarette smoke, pesticides, air pollution, ultraviolet light and radiation which are all too common in the environments in which most of us live. Stress and excessive exercise can also produce large amounts of free radicals.
Vitamins may exert their antioxidant effects by acting as circuit breakers. They insert themselves into the free radical chain reaction and are altered without generating further free radicals. Antioxidants interact to protect each other. Vitamin C can react with a damaged vitamin E molecule and convert it back to its antioxidant form. Vitamin C is then returned to its original form by another antioxidant known as glutathione. This may explain the result of studies which show that vitamin C enhances the protective effects of vitamin E.
Free radical damage
- Free radical attacks on DNA, which is the genetic material of the cells, cause cells to die or mutate and possibly become cancerous. Free radicals may be involved in cancers of the lungs, cervix, skin, stomach, prostate, colon and esophagus.
- Free radicals also attack blood fats which may lead to heart and blood vessel disease. When the LDL type of cholesterol reacts with free radicals it becomes damaged and this may lead to atherosclerosis. Unless LDL cholesterol becomes damaged it does not seem to be harmful. Thus the damaging of LDL cholesterol is a critical link between high blood cholesterol and the build-up of vessel-blocking plaques. Atherosclerosis is the major cause of hardening of the arteries and therefore of heart attacks. Levels of another type of cholesterol, known as HDL cholesterol, which may protect against cardiovascular disease, may be lowered by free radical activity.
- Free radicals can also damage cellular enzymes. The processes which depend on these enzymes slow or stop, leading to cell damage and death. Dormant enzymes can also be activated and this can result in tissue damage.
- Cells contain components called mitochondria which are responsible for respiration and energy production. Free radicals can damage mitochondria, affecting the ability of the cell to produce the energy it needs to function.
- Substances which are toxic to nerves can also be released by free radicals, leading to nerve and brain damage, such as that seen in Parkinson's disease.
- Free radicals may be involved in the loss of transparency of the lenses of the eye, leading to cataracts and macular degeneration.
- Free radicals may be involved in the inflammatory response seen in rheumatoid arthritis and asthma.
- Free radicals may also damage sperm causing infertility and birth defects. They may also be involved in ulcers and other digestive tract disorders, liver damage and reduced resistance to infection and disease.
Reducing free radical damage
Damage from free radicals can be minimized by avoiding excessive exercise, pollution, pesticides, cigarette smoke and other dangerous environmental factors. Eating a diet of foods rich in antioxidants is also extremely important. There are many powerful antioxidant compounds in foods which can strengthen the body's defense systems.
Individual levels of antioxidants depend on many factors including lifestyle, state of health, diet and heredity. People vary in their ability to absorb and metabolize different antioxidants, just as they do in the case of other nutrients. Some people may be able to obtain all the antioxidants they need from a healthy diet and others may benefit from supplements. However, until accurate tests are readily available it is not always easy to identify those who do have higher needs. With diseases where prevention is most important, it may be too late to reverse the adverse effects of free radical damage once susceptible people are identified. Several tests are being developed to measure oxidant stress. Such tests might establish the doses of antioxidant vitamins necessary to provide protection in individuals.
Antioxidants and the aging process
Aging is the accumulation of various adverse changes in cells and tissues that increase the risk of death. Evidence is growing that free radicals are an underlying cause of aging as the biological markers of the process are the same as those caused by free radical damage.
As the mitochondria are where most of the oxygen reactions in the cell occur, they may be the most susceptible to damage by free radicals. It has been suggested that the rate of damage, and therefore aging, in mitochondria may determine how long a person lives. The ability of antioxidants to reduce this damage explains their possible role in slowing the aging process. Research into chemicals which could slow the damage to mitochondria without decreasing energy production is in the early stages but it is expected to increase.
Due to their effects on mitochondria and other elements such as cell membranes and genetic material, free radicals may aggravate the breakdown and sagging of tissues and deterioration of bodily organs involved in the aging process. Many diseases commonly associated with aging, including cancer, heart disease and psychological disorders, appear to be prevented or improved by increasing intake of antioxidants. High levels of antioxidants also increase the effectiveness of the immune system, making older people less susceptible to life-threatening infections.
Experiments with aging animals show that the effectiveness of the body's antioxidant system decreases with age, possibly because of reduced dietary intake, absorption or increased nutrient needs. A steady supply of antioxidant vitamins and minerals should enhance the body's natural defense mechanisms and improve the quality and length of life.
Antioxidant supplements
For a person whose diet does not provide sufficient amounts of the antioxidant vitamins, it may be worth considering taking extra amounts as supplements. Research shows that the protective effects of antioxidant vitamins occur when they are taken at doses much higher than the RDAs. Studies which look at the anticancer effects of vitamin C often use doses of around 1000 mg. This is the amount in 14 oranges. Studies looking at the heart protective effects of vitamin E have used doses of 800 IU (536 mg alpha TE). This is the amount in around eight cups of sunflower seeds.
Those who regularly eat five to nine large servings of fruit and vegetables every day may be able to get enough vitamin C and beta carotene, but a large amount of high fat vitamin E-rich foods would be necessary to reach the levels that have been used to show protective effects.
Antioxidant vitamins are well-tolerated and free from toxicity, even in high doses except in unusual circumstances. In those who have a history or a family history of disease; are under stress; smoke; or live in a polluted environment; antioxidant supplements may be recommended. Suggested doses are:
- vitamin C - 100 to 1000 mg
- beta carotene - 10 to 30 mg
- vitamin E - 67 to 500 mg alpha TE
- selenium - 100 to 200 mcg
Other antioxidants
Aside from antioxidant vitamins and minerals, there are several other types of antioxidants available both in foods and supplements. Many of these belong to a family of plant chemicals called flavonoids. There are also several herbs which have antioxidant activity. These include cayenne or chilli pepper (Capsicum annuum), ginger (Zingiber officinale), garlic (Allium sativum), turmeric (Curcuma longa), ginkgo (Ginkgo biloba) and bilberry (Vaccinium myrtillus).