The research, published in The BMJ, and based on a systematic review of studies and meta-analysis of individual participant data, looked at the effect of vitamin D supplementation on acute respiratory tract infections.
Led by Professor Adrian Martineau at Queen Mary University of London, the study found that vitamin D supplementation resulted in a 12% reduction in the proportion of participants experiencing at least one acute respiratory tract infection.
It concluded that: “Vitamin D supplementation was safe and it protected against acute respiratory tract infection overall.”
The study added that it supported “the introduction of public health measures such as food fortification to improve vitamin D status in settings where profound vitamin D deficiency is common”.
However, The BMJ also published a linked editorial comment by Dr Mark Bolland from the University of Auckland and Professor Alison Avenell from the University of Aberdeen, who claimed there were reasons for viewing the headline result cautiously.
“Eight trial level meta-analyses have examined this topic since 2012, with conflicting findings: three reported benefits and five [reported] no consistent benefits from vitamin D,” they said.
“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. It seems unlikely that the general population would consider a 2% absolute risk reduction sufficient justification to take supplements,” Bolland and Avenell added.
They also found 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”.
Professor Louis Levy, head of nutrition science at PHE, said the evidence on vitamin D and infection was “inconsistent” and this study “does not provide sufficient evidence to support recommending vitamin D for reducing the risk of respiratory tract infections”.
Bone and joint health
However, Levy reiterated PHE’s recommendation that “certain population groups” take vitamin D supplements all year round to protect bone and joint health. PHE’s guidance was based on evidence by the Scientific Advisory Committee on Nutrition (SACN), published last year.
Catherine Collins, registered dietitian and spokeswoman for The British Dietetic Association, acknowledged that vitamin D had the most complex backstory of all the nutrients we needed.
She said: “This paper confirms the established role of vitamin D on the immune system, and confirms that for the vitamin D deficient, supplements have an important role in supporting immune function.”
Meanwhile, Dr Benjamin Jacobs, consultant paediatrician at the Royal National Orthopaedic Hospital, claimed that the study was “a major step forward” which showed “strong evidence of benefit and safety of vitamin D supplements”.
“Martineau’s study shows a clear reduction in respiratory infection in people taking vitamin D, including patients of all age groups,” he said.
The British Nutrition Foundation has developed a resource showing the vitamin D content of different foods and how vitamin D requirements can be met, available here.