Oct. 2, 2012 -- Looks like we may have to cross out another supposed way to prevent the common cold.
A new study shows that people who took large doses of vitamin D were as likely to catch colds, and suffer with them as long, as those who took placebo pills.
There were reasons to think otherwise. Various studies have suggested that vitamin D plays a protective role in the immune system. Vitamin D deficiency in children has been linked to higher rates of pneumonia and upper respiratory tract infections. And because the body makes vitamin D when in the sun, lower levels tend to occur in the winter, otherwise known as cold season.
In the new study, New Zealand researchers assigned 322 healthy adults to take either vitamin D supplements or a placebo once a month for 18 months. For the first two months, those assigned to vitamin D took 200,000 IU (international units) once per month. For the rest of the study, they took 100,000 IU once per month.
The Institute of Medicine recommends that people 1-70 years old take in 600 IU of vitamin D daily, and that people over 70 years take in 800 IU daily.
This high-dosing regimen used in the study was chosen to achieve blood levels of vitamin D that had been linked to the lowest risk of disease in some previous studies.
Participants were asked to contact study staff whenever they came down with symptoms of a cold, such as a runny nose or sore throat. A staff member then visited to do a swab test and have the participant complete a survey about their symptoms.
The swabs were used to test for a variety of viruses that cause colds and the flu.
Study Results Not Perfect
By the end of the study, both the vitamin D group and the placebo group had averaged just under four upper respiratory tract infections per person, according to the researchers' report in this week’s Journal of the American Medical Association. With each episode, symptoms lasted an average of 12 days in both groups.