Vitamin D Supplements Don't Prevent Respiratory Infections

Vitamin D deficiency has been associated with many medical problems, but whether repletion improves clinical outcomes is still largely unclear. U.S. researchers who were conducting a large blinded trial of vitamin D₃ and calcium supplementation for preventing large bowel adenomas included a substudy to look at rates of upper respiratory tract infection among participants.

Participants were healthy adults (age range, 45–75) whose initial vitamin D levels exceeded 12 ng/mL. During a period that spanned two winter “flu seasons,” 399 participants who were receiving daily vitamin D (1000 mg) and 360 participants who were receiving placebo reported identical rates of both serious and trivial upper respiratory infections. These results were unaffected by adjustment for receipt of supplemental calcium, receipt of flu vaccine, or body-mass index. Rates were similar during the first winter of the study, which overlapped the H1N1 flu pandemic (2009–2010), and during the subsequent one without pandemic influenza. Mean serum vitamin D levels did not differ among participants who did and did not report respiratory illnesses.