Vitamin C for Colds
Vitamin C has been long used as a treatment for the common cold, but you might be surprised at how conflicted the evidence is. Although it seems to boost some aspects of the immune system, studies do not show that vitamin C -- at least in doses of 1 gram per day -- helps prevent colds in most people, though it may be helpful in preventing colds in people who are exposed to cold weather or who undergo extreme exercise.
As a treatment, the evidence is somewhat better. Some studies show that vitamin C can reduce the duration of a cold by as much as 24 to 36 hours. However, other studies show that even very high doses -- 3 grams a day -- have no effect.
Keep in mind that the high doses of vitamin C sometimes recommended for cold and flu can upset the stomach and even cause diarrhea in some people. Leopold is particularly wary of using high doses of vitamin C in children.
Echinacea for Colds
Once again, the evidence is mixed. Although some studies do not show that echinacea works as a treatment, others show it can reduce the length and severity of colds by 10% to 30%.
Despite the confusion, many experts are fairly sure that echinacea can help treat colds. Leopold points out that some of the conflicting study results may stem from researchers testing different species of echinacea. So far, the best evidence supports taking echinacea purpurea, which may also work better for adults than for children.
Can echinacea also help prevent you from catching cold or flu viruses? Most studies say no.
Echinacea does have some mild risks. If you have allergies to ragweed or certain flowers in the daisy family, don't take echinacea before talking to your doctor. It may also not be safe for people with certain diseases that affect immunity, such as autoimmune conditions like rheumatoid arthritis and lupus, Leopold says.
Zinc for Colds
Zinc lozenges have become a popular treatment for the common cold. Forms of zinc available on the market include zinc acetate, zinc citrate, zinc gluconate, zinc picolinate, and zinc sulfate.
Taking zinc, either as a syrup or lozenge, through the first few days of a cold may shorten the misery of an upper respiratory infection, the latest research shows. The research -- a review of 15 past studies on the subject -- also found that zinc appeared to prevent colds in people who used it over the course of about five months.
Other studies show no benefit, which may be partly due to the different formulations of zinc.
Some experts suggest that zinc should not be taken for long periods of time. If it is, it may induce a copper deficiency in the body.
Can zinc also help prevent colds or the flu? So far, there isn't good evidence to support zinc lozenges for cold or flu prevention.