A new study conducted in The Journal of the American Medical Association says there is no evidence that taking vitamin D supplements prevents the common cold.
The study says the number of upper respiratory infections wasn't any lower with large monthly doses of vitamin D than with placebo, at a mean of 3.7 versus 3.8 per person, for a non-significant risk reduction of just 3 percent, reports ABC News.
It has long been suggested that taking vitamin D strengthens the body's immune system, but now, Dr. David R. Murdoch of the University of Otago in Christchurch, New Zealand and his team found that taking the vitamin actually has no significant effect.
The study said, in those tested, missed workdays and duration of symptoms likewise were similar between those who took the vitamin over the period of a year,and those who didn't, the group reported in the Oct. 3 issue of the JAMA.
"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 (upper respiratory tract infections). This result remained unchanged when the analysis included winter season or baseline 25-OHD levels," the study says.
However, Murdoch did write that is it possible that vitamin D may prevent URTIs in "other populations."
"It is possible that an effect may be observed in a population with a higher prevalence of vitamin D deficiency, as occurred in a recent trial of vitamin D supplementation to reduce exacerbations of chronic obstructive pulmonary disease," the study read. "In that trial, vitamin D supplementation significantly reduced exacerbations only in patients with baseline 25-OHD levels less than 10 ng/mL."
The study said healthy adults in developed countries who are already keeping their vitamin D in the range recommended for bone health don't need an extra boost of the Vitamin.
"It's very important, however, to keep in mind that this group had relatively normal levels to start with, and so this might not apply to people with lower levels, with actually a vitamin D deficiency," study co-author Dr. Carlos A. Camargo Jr. of Massachusetts General Hospital in Boston said to ABC.
He said, for example, a daily dose of the vitamin has been proven to have a "dramatic impact" on vitamin D-deficient children in Mongolia, actually cutting in half the number of them who contract upper respiratory infections.