A new study claims vitamin D supplementation is indicated in reducing respiratory tract infections, but the authors of an accompanying editorial are not so sure

The paper, Vitamin D supplementation to prevent acute respiratory tract infections: systemic review and meta-analysis of individual participant data, comprised an analysis of 25 eligible randomised controlled trials (total 11,321 participants, aged 0-95).

Vitamin D supplementation reduced the risk of such infections among all participants by 12% in the adjusted analysis.

“Vitamin D supplementation was safe and it protected against acute respiratory tract infection overall. Patients who were very vitamin D deficient and those not receiving bolus doses experienced the most benefit,” wrote the authors, an international research team led by the Queen Mary University of London.

To date, randomised controlled trials of vitamin D supplementation for the prevention of acute respiratory tract infection have yielded conflicting results.

The authors say their findings support a “major new indication” for vitamin D supplementation: the prevention of acute respiratory tract infection.

They say the findings also support the introduction of public health measures such as food fortification to improve vitamin D status, particularly in settings where profound vitamin D deficiency is common.

But in an accompanying editorial, Mark J Bolland from the University of Auckland and Alison Evenell from the University of Aberdeen say the results should probably not change clinical practice.

“There are reasons for viewing the headline result cautiously. In absolute terms, the primary result is a reduction from 42% to 40% in the proportion of participants experiencing at least one acute respiratory tract infection,” they write.

“It seems unlikely that the general population would consider a 2% absolute risk reduction sufficient justification to take supplements. Furthermore, the definition of acute respiratory tract infection varied between studies, consisting of a mixture of diverse conditions such as acute otitis media, laboratory-confirmed influenza, self-reported colds, parent-reported colds or chest infections, or radiograph-confirmed pneumonia.

“It is difficult to know whether a reduction in this mixture of conditions is applicable to the general population and how it should be interpreted clinically.

“The results are heterogeneous and not sufficiently applicable to the general population. We think that they should be viewed as hypothesis-generating only, requiring confirmation in well designed adequately powered randomised controlled trials.

“Several very large such randomised controlled trials of vitamin D supplements will report on the effects on respiratory infections within the next few years. These trials have not targeted individuals with very low serum concentrations of vitamin D, and there is still a need for trials in these population groups.”

And Dr Rachel Neale, from the University of Queensland, one of the original study’s co-authors, told MJA InSight vitamin D supplementation may not be necessary in Australia.

According to the Australian Health Survey, only 7% of Australians had vitamin D levels under 30 nmol/L.

“Until we have evidence that shifting the 25-hydroxycitamin D distribution in the entire population, rather than treating deficiency, is beneficial, I’m not sure food fortification is appropriate,” she told MJA InSight.

In a practice paper published late last year in the BMJ, A/Prof Bolland and Prof Avenell, with A/Prof Andrew Grey from the University of Auckland, also consider whether adults should take vitamin D supplements to prevent bone disease.

“Osteomalacia is an uncommon but serious illness that can readily be prevented,” they write. “People at high risk should be counselled about sunlight exposure and diet, and low-dose vitamin D supplements (400-800 IU/day) can be considered on an individual basis.

“Otherwise, we conclude that current evidence does not support the use of vitamin D supplementation to prevent disease.”