Many of readers report a reduction (not absence) of colds and flu with 5,000 IU daily doses of vitamin D. However, hundreds of media outlets are reporting on a well-conducted JAMA study that showed no benefit for vitamin D in preventing the common cold.
The randomized controlled trial, led by Dr David R Murdock of the University of Otago in New Zealand, found that 200, 000 IU per month for two months followed by 100,000 IU per month of vitamin D for 16 months in 161 patients did not prevent either the diagnosis or complaint of the common cold. The study included viral cultures, rigorous efforts to capture all infections, vitamin D given during monthly doctor visits, and initial and follow up vitamin D levels. The average initial level in the treatment group was 29 ng/ml and 18 months later, the mean level was approximately 50 ng/ml, with no side effects.
However, only 13 of the 161 placebo patients had levels below 20 ng/ml and only 5 of the 322 total patients had levels less than 10 ng/ml to begin the study. That is, the placebo group had relatively high levels (mean of 28 ng/ml initially), compared to most populations, and all but 13 patients had levels above 20 ng/ml for most of the study, apparently from sun exposure.
Compare Dr. Murdock’s results to the result of another study, one in the Lancet by Dr Adrain Martineau and colleagues, who, as a secondary end-point, assessed upper respiratory tract infections over two months in patients given 2.5 mg (100,000 IU every two weeks for eight weeks for ancillary treatment of TB.
They found a six-fold reduction in upper respiratory infections, but their English population was severely vitamin D deficient to begin with.
In addition, two randomized controlled trials in children, one in Japan and one in Mongolia, both given daily vitamin D, showed a reduction in upper respiratory tract infections. Both studies had placebo arms. In the Mongolian study, the investigators measured vitamin D deficiency in the placebo arm, and it was much worse than in the JAMA study, a point the JAMA authors note.
In yet another secondary end point in a randomized controlled trial, 2,000 IU/day of vitamin D in African Americans with initial low levels reported a dramatic reduction in respiratory infections. Both the report and our group’s reply are free to read and download in its entirety.
Thus, the JAMA study leaves us with a number of possibilities:
I am unaware of any study that used significant daily doses for an entire winter that was negative. What is your experience with daily doses of vitamin D and infections?