The Common Cold
What is it?
The common cold is one of the most frequently occurring illnesses in the world. It is caused by more than 200 known viruses that infect the upper respiratory tract. Symptoms include congestion in the nose, sore throat, headache, nasal discharge and sneezing. The larynx and lungs can also be affected. The average person catches a cold three times a year. Young children are particularly susceptible as their immune systems are still developing and may catch colds as often as eight times a year. Although most cases are mild and usually last about a week, colds are the leading cause of visits to the doctor and days off work and school.
Treatment of the common cold
In spite of the fact that it is a very common infection, both the causes and symptoms of the common cold are complicated and difficult to treat. There are still no cures for the many viruses that cause the common cold and the medicines available in local pharmacies may help relieve the symptoms but they cannot cure the cold, which has to run its course. Antibiotics are not effective against cold viruses and do not improve cold symptoms. Taking antibiotics unnecessarily can lead to antibiotic resistance, a potentially dangerous situation in which infection-causing bacteria become immune to the effects of certain antibiotics. Relaxation, enough sleep, water, staying warm and aspirin may be useful in treating cold symptoms.
Maintaining a strong immune system is important in avoiding colds. Stress and a poor diet can damage the immune system; and nutrients such as antioxidants, which enhance immunity, are important for the prevention of any infection. Research into the effects of specific nutrients in preventing and treating colds has focused on vitamin C and zinc.
Vitamins, minerals and the common cold
Vitamin C
In 1970, Nobel Prize winner Linus Pauling wrote a book called Vitamin C and the Common Cold in which he claimed that vitamin C was effective in reducing the severity of symptoms and the duration of a cold. These claims have caused much controversy in the medical community. Since 1971, many studies have investigated the ability of vitamin C in doses of 1 g per day or greater to affect the common cold. These studies have produced conflicting results with large variations in the benefits observed, and many doctors feel that the results are not clinically significant. There does not seem to be consistent evidence that vitamin C supplementation reduces the incidence of the common cold in the general population. Most studies show that the doses of vitamin C which are effective against colds are much higher than typical dietary intakes and at least 1 g per day may be necessary to show benefits.
Vitamin C treatment seems to have several effects, including reducing blood levels of histamine which can trigger tissue inflammation and a runny nose. As an antioxidant, Vitamin C may also protect the immune cells and surrounding tissue from damaging oxidative reactions that occur when white blood cells become activated and release oxidizing compounds to fight bacteria.1
It seems likely that the effects of supplementation are greater in those with low dietary vitamin C intake. In general, men have lower vitamin C levels than women. In four studies with British girls and women, vitamin C supplementation had no marked effect on the common cold. However, in four studies with British male schoolchildren and students, a reduction in common cold occurrence was found in groups supplemented with vitamin C.2
Some research suggests that vitamin C supplementation may be beneficial for people who do heavy exercise and who have problems with frequent upper respiratory infections. Three placebo-controlled studies have examined the effect of vitamin C supplementation on common cold occurrence in people under acute physical stress. In one study the subjects were school children at a skiing camp in the Swiss Alps; in another they were military troops training in Northern Canada; and in the third they were participants in a 90 km running race. In each of the three studies, a considerable reduction in common cold incidence in the group supplemented with vitamin C at levels of 600 mg to 1000 mg per day was seen.3
Zinc
Zinc may be effective in treating the common cold due to its antiviral and antibacterial effects and its ability to enhance immune system function. There have been several studies of the effects of zinc lozenges on the common cold. Some studies have shown benefit while others have not. The authors of a 1998 review of the trials concluded that treatment of the common cold with zinc gluconate lozenges, using adequate doses of elemental zinc, is likely to be effective in reducing duration and severity of cold symptoms. Most benefit is seen if the lozenges are started immediately after the onset of symptoms.4
In a 1996 randomized, double-blind, placebo-controlled study, researchers tested the effect of zinc gluconate lozenges on the common cold. The study involved 100 participants, and patients in the zinc group received a lozenge containing 13.3 mg of zinc every two hours. The lozenges reduced the duration of cold symptoms from 7.6 days to 4.4 days. However, some people did not like the taste of the lozenges.5
The type of zinc salts used in the lozenges also appears to be important, and the addition of citric or tartaric acids seems to reduce the benefit as these substances bind to zinc ions. A 1997 study suggests that zinc acetate lozenges may be more effective in treating colds than zinc gluconate. More zinc ions are released from zinc acetate under physiological conditions.6
The most recent study, published in the Journal of the American Medical Association in 1998 did not find zinc lozenges to be effective. The study involved 249 students in grades one through 12, some of whom were given 10 mg zinc lozenges five or six times a day for three weeks, and some of whom were given placebo lozenges containing no zinc. The study showed that it took children taking zinc lozenges an average of nine days to get over all their cold symptoms, which was the same amount of time for children who took placebo lozenges. The study also found that children who took zinc lozenges had a higher rate of adverse effects: bad taste reactions; nausea; mouth, tongue, or throat irritation; and diarrhea.7
Herbal medicine and the common cold
Useful herbs for cold prevention include those used to boost immunity such as echinacea (Echinacea angustifolia) and astragalus (Astragalus membranaceous). Echinacea can also be useful at the onset of a cold as can elderflowers (Sambucus nigra), cayenne (Capsicum spp.), garlic (Allium sativum), goldenseal (Hydrastis canadensis). Other herbs that are useful include sage (Salvia officinalis), thyme (Thymus vulgaris), horseradish (Armoracia spp.), peppermint (Mentha piperita), yarrow (Achillea millefolium) and limeflowers (Tilia europea).