The study, published in the Journal of the American Medical Association, included 322 healthy people living in New Zealand. Their vitamin D levels were measured and they were assigned to either a placebo group or a vitamin D group that received 200,000 IU of vitamin D3 (the type of vitamin D normally found in the human body) in tablet form once per month for two months, followed by 100,000 IU per month for the rest of the study.
During the study, which lasted 18 months and included two winters, vitamin D levels were checked periodically and monthly questionnaires were used to gather information about colds and other upper respiratory tract infections.
No difference was found in the number, severity, or duration of colds and other upper respiratory tract infections in people in the vitamin D and placebo groups. The 13 people who had low vitamin D levels and the 5 who were deficient were no more likely to experience colds or have more intense or longer lasting symptoms than people with normal levels. However, because of the small number of people in the study with deficient levels, the researchers were not able to say for sure whether vitamin D3 could prevent colds in people with vitamin D deficiency.
“The main finding from this study is that a monthly dose of 100,000 IU of vitamin D3 in healthy adults did not significantly reduce the incidence or severity of upper respiratory tract infections,” the study’s authors said.
What is the cure for the common cold? There is still no definitive answer but here are some things you can do to improve the chance that you will be healthy all winter: