Posted on Sat, 20 Oct 12
A recent clinical trial has been reported in the media as evidence that there is no effect of vitamin D supplementation against colds and flu. But the headlines are misleading.
In the study some 320 healthy adults received oral vitamin D3 supplements or placebo for 18 months but by study's end, neither the number of upper respiratory tract infections nor the severity of illness differed significantly between the groups (1).
One of the strengths of this study is that they used a good dose of vitamin D and it did significantly raise blood levels. But is this conclusive evidence that vitamin D does not prevent infection? Not really.
The main issue is that the people in the study were not typically vitamin D deficient. The average level of vitamin D (25-OHD) before the study was 29 ng/mL which means they were close to the adequate vitamin D range (>30 ng/ml). Only 5 participants (1.6%) had levels less than 10 ng/mL.
If your vitamin D levels are already ok there is a good chance taking more wont be of major benefit. In another trial vitamin D supplementation significantly reduced chronic obstructive pulmonary disease exacerbations only in patients with baseline 25-OHD levels less than 10 ng/mL (2). And a recent trial in children with a baseline level of 7 ng/mL found vitamin D to reduce colds and flu by 48% (3).
So what this study really tells us is that if you are a healthy adult and have near-normal vitamin D levels supplementation does not appear to lower upper respiratory tract infections.
1. Murdoch D, et al. Effect of Vitamin D3 Supplementation on Upper Respiratory Tract Infections in Healthy Adults. JAMA. 2012;308(13):1333-1339.
2. Lehouck A, Mathieu C, Carremans C, et al. High doses of vitamin D to reduce exacerbations in chronic obstructive pulmonary disease: a randomized trial. Ann Intern Med. 2012;156(2):105-114
3. Camargo CA Jr, Ganmaa D, Frazier AL, Kirchberg FF, Stuart JJ, Kleinman K, Sumberzul N, Rich-Edwards JW. Randomized trial of vitamin d supplementation and risk of acute respiratory infection in mongolia. Pediatrics. 2012 Sep;130(3):e561-7.