Vitamin D supplements protect against acute respiratory infections, according to a UK study published in the BMJ. (1)
The meta-analysis of 25 randomised controlled trials involving almost 11000 participants, aged 0 to 95 years, found a significant overall protective effect of vitamin D supplementation against acute respiratory infections, with the number needed to treat estimated at 33.
And if you just look at those people who were found to be profoundly vitamin D deficient at baseline, the resulting protective effect of supplementation was even more dramatic with the number needed to treat plummeting to just four.
Vitamin D’s role in bone health is well-documented and well known, and there have been many studies suggesting the vitamin also protects against a whole host of other illnesses from MS to depression.
However, whether vitamin D supplementation can protect against respiratory tract infections has been particularly controversial, with studies to date showing conflicting results.
But now the authors of this study are claiming a definitive result.
“Our study reports a major new indication for vitamin D supplementation: the prevention of acute respiratory tract infection,” they say.
They add that their findings lend support to the push to introduce public health measures to improve vitamin D levels in the community, such as food fortification.
On face value the recommendation for food fortification is likely to have more relevance in the UK, where the researchers are based, than here in Australia but there is increasing evidence that vitamin D deficiency is an issue here particularly in certain groups – people in residential care, dark-skinned people and people who cover their skin for cultural or religious reasons.
According to ABS just under one in four (23%), or four million adults in Australia, has a vitamin D deficiency, which comprised 17% with a mild deficiency, 6% with a moderate deficiency and less than 1% with a severe deficiency. (2)
So that’s a lot of people who could potentially benefit from supplementation even if it’s only for the protection against respiratory infections.
Two other considerations to note when reviewing this study.
Firstly, in addition to finding that people who were profoundly vitamin D deficient benefitted the most from supplementation in terms of protection against colds and such, the researchers also found that taking a daily or weekly supplement was more beneficial than taking bolus doses of vitamin D.
The reason why regular rather than intermittent supplementation should work isn’t clear but the study authors suggest it is possibly due to the wide fluctuations in vitamin D levels seen with bolus dosing, adversely affecting the ability of the active metabolite to support the immune response to respiratory pathogens. Bottom line – people are better off taking vitamin D supplements regularly rather than just having bolus doses when a blood test reveals their levels are low.
The other important finding from the study, was that Vitamin D supplementation is safe.
“Use of vitamin D did not influence risk of serious adverse events of any cause or death due to any cause,” the authors stated.
And even though a number of cases of hypercalcaemia and renal stones did occur, they were equally represented in both the intervention and control arms of the studies included in the meta-analysis.
1. Martineau AR, Joliffe DA, Hooper RL et al. Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data. MBJ 2017;356:i6583
2. Australian Bureau of Statistics