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Vitamin D may do nothing to prevent common colds

If you're looking for a surefire way to prevent a common cold, you may have to wait a bit longer. A new study finds one previously trusted remedy -- a dose of vitamin D -- does nothing to ward off the sniffles.

Adults catch on average two to four colds a year, and children contract up to 10, according to the BBC. Previous experiments have shown that vitamin D may be able to give a boost to the immune system and other studies have shown that people with low levels of vitamin D were more likely to develop colds or other forms of upper respiratory tract infections (URTIs).

Researchers in New Zealand tested out the vitamin D theory in an 18-month study. A group of 322 healthy adults were told either to take a vitamin D supplement or a placebo. Those who took the vitamin were given 200,000 international units (IU) each month or about 6,600 units a day for two months and 100,000 IU once a month or about 3,300 daily for the rest of the study. The Institute of Medicine of the National Academies in Washington D.C. recommends that people under 70 consume 600 IU of vitamin D daily, and people over 70 years take 800 IU daily.

The participants were asked to call researchers if they had symptoms of a common cold like runny nose or sneezing. Swabs were taken to determine if they had the cold virus.

At the end of the study there were 593 episodes of respiratory infections -- on average 3.7 colds per person -- in the vitamin D group and 611 episodes -- on average 3.8 colds per person -- in the placebo group. Each group averaged 12 missed days of work because of their illness. Statistically speaking, there was no real difference in cold risk between vitamin D and placebo pills when chance is taken into consideration.

"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 URTIs. This result remained unchanged when the analysis included winter season or baseline [vitamin D] levels," the authors wrote.

Dr. Jeffrey Linder, assistant professor at Harvard Medical School and an internal medicine specialist at Brigham and Women's Hospital in Boston, said in an accompanying editorial that vitamin D should be added to the Cochrane Collaboration's registry of ineffective, possibly harmful common cold remedies. The list includes Chinese herbs, intranasal corticosteroids, asthma drug intranasal ipratroprium, extract of South African plant Pelargonium sidoides, nasal irrigation, extra fluid intake, Echinacea, zinc, steam inhalation, vitamin C, garlic, antihistamines, or antiviral drugs.

But Ronald Eccles, director of the Common Cold Center and professor at Cardiff School of Biosciences at Cardiff University in Cardiff, Wales, told the BBC that it doesn't necessarily mean that Vitamin D can't help you. He said it helps boost the immune system especially during the winter season, and he personally takes it every year to help ward of illness.

"There is sufficient information to indicate that vitamin D is a vital vitamin for the immune system," he said.

The study was published in the Oct. 2 issue of the Journal of the American Medical Association.

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