Taking vitamin D supplements protects against acute respiratory infections including colds and flu, a major clinical trial has shown.
The Department of Health-funded study, published in the BMJ, is described as ‘the most robust evidence yet’ that vitamin D has wider protective benefits beyond improving bone and muscle health.
The study could have implications for public health policy, with researchers recommending fortification of foods with vitamin D in response to finding that supplements were as effective as the flu jab. They said it comes as this type of infection is the commonest reason for GP consultations and days off work.
Researchers believe that the protective effect against respiratory infections comes from boosting levels of antimicrobial peptides in the lungs. They think also helps explain why vitamin D protects against asthma attacks.
The team, from Queen Mary University of London (QMUL) analysed data from around 11,000 participants in 25 clinical trials carried out in 14 countries across the world, some which concluded there was an effect and some which did not.
They concluded that daily or weekly vitamin D supplements halved the risk of acute respiratory in people with the lowest baseline vitamin D levels, below 25 nanomoles per litre (nmol/L).
The effect was more modest in people higher baseline vitamin D levels, but these still saw a 10% risk reduction.
On the whole, the study concluded that infection risk reduction from taking regular vitamin D supplements was equal to that achieved with injectable flu vaccine.
Lead researcher Professor Adrian Martineau from QMUL said: ‘This major collaborative research effort has yielded the first definitive evidence that vitamin D really does protect against respiratory infections. Our analysis of pooled raw data from each of the 10,933 trial participants allowed us to address the thorny question of why vitamin D “worked” in some trials, but not in others.’
‘The bottom line is that the protective effects of vitamin D supplementation are strongest in those who have the lowest vitamin D levels, and when supplementation is given daily or weekly rather than in more widely spaced doses.’
He added that ‘by demonstrating this new benefit of vitamin D, our study strengthens the case for introducing food fortification to improve vitamin D levels in countries such as the UK where profound vitamin D deficiency is common’.
Professor Hywel Williams, director of the NIHR Health Technology Assessment (HTA) Programme at the National Institute for Health Research (NIHR), which funded the work, said that the ‘interesting findings of this large study are worthy of serious further debate’.