Taking vitamin D supplements could help prevent acute respiratory tract infections, particularly among very deficient individuals, according to UK researchers.
The team from Queen Mary University of London said their findings “support the introduction of public health measures such as food fortification to improve vitamin D status in settings where profound vitamin D deficiency is common”.
“Our study reports a major new indication for vitamin D supplementation”
They highlighted that infections, from the common cold to bronchitis and pneumonia, had been linked with low blood levels of vitamin D.
Some studies had shown that vitamin D could trigger immune responses to certain bacteria and viruses, but they noted that trials of supplements to prevent infections had led to conflicting results.
The international team of researchers set out to assess the overall effect of vitamin D supplements on risk of acute respiratory tract infection, and to identify factors modifying this effect.
They conducted a systematic review and meta-analysis of data from 25 randomised controlled trials of vitamin D supplementation, involving 11,321 participants aged 0-95 years.
Vitamin D supplementation resulted in a 12% reduction in the proportion of participants experiencing at least one acute respiratory tract infection, they concluded in the British Medical Journal.
They calculate that 33 patients would need to take vitamin D supplements to prevent one acute respiratory tract infection.
Further analyses among specific groups showed benefit was greater in those receiving daily or weekly vitamin D without bolus doses.
The protective effect in this group were strongest in those with severe deficiency – less than 25nmol/L baseline blood levels – with only four needing to take supplements to prevent one acute respiratory tract infection.
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The researchers said: “Our study reports a major new indication for vitamin D supplementation: the prevention of acute respiratory tract infection.
“Our results add to the body of evidence supporting 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,” they said.
But, in a linked editorial in the same journal, other researchers claimed that a clinically useful effect remained uncertain and required confirmation in well-designed “adequately powered randomised controlled trials”.
Mark Bolland, from the University of Auckland, and Alison Avenell, from the University of Aberdeen, suggested it was yet another hypothesis about vitamin D supplementation that needed testing.
They argued that the results were “heterogeneous and not sufficiently applicable to the general population”, and should be viewed as hypothesis-generating only.
“Current evidence does not support the use of vitamin D supplementation to prevent disease, except for those at high risk of osteomalacia (weak bones and muscles due to low blood vitamin D levels, currently defined as less than 25nmol/L),” they said.