Vitamin D protects against colds and flu, finds major global study

Date: 16 February 2017

Vitamin D supplements have been found to protect against acute respiratory infections including colds, flu and pneumonia, according to a study funded by the NIHR.

The study provides the most robust evidence yet that vitamin D is beneficial for something other than bone and muscle health, and could have major implications for public health policy, including the fortification of foods with vitamin D to tackle high levels of deficiency in the UK.

The results, published in the BMJ, are based on a new analysis of raw data from around 11,000 participants in 25 clinical trials conducted in 14 countries including the UK, USA, Japan, India, Afghanistan, Belgium, Italy, Australia and Canada. Two of these were large NIHR Programme Grants for Applied research studies. Individually, the trials yielded conflicting results, with some reporting that vitamin D protected against respiratory infections, and others showing no effect.

Lead researcher Professor Adrian Martineau from Queen Mary University of London (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 the 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.

“Vitamin D fortification of foods provides a steady, low-level intake of vitamin D which has virtually eliminated profound vitamin D deficiency in several countries. 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.”

Vitamin D – the ‘sunshine vitamin’ – is thought to protect against respiratory infections by boosting levels of antimicrobial peptides - natural antibiotic-like substances – in the lungs.

Daily or weekly supplementation halved the risk of acute respiratory infection in people with the lowest baseline vitamin D levels, below 25 nanomoles per litre. However, people with higher baseline vitamin D levels also benefited, although the effect was more modest (10 per cent risk reduction).

This observation suggests that the current threshold of 25 nmol/L used to define vitamin D deficiency in the UK may be too conservative, and that a higher threshold (such as 50 nmol/L, used in Europe and the US) may be more appropriate.

Acute respiratory infections are a major cause of global morbidity and mortality. Upper respiratory infections such as colds and flu are the commonest reason for GP consultations and days off work. Acute lower respiratory infections such as pneumonia are less common, but caused an estimated 2.65 million deaths worldwide in 2013. Vitamin D supplementation is safe and inexpensive, so reductions in acute respiratory infections brought about by vitamin D supplementation could be highly cost-effective.

Professor Hywel Williams, Director of the NIHR HTA Programme said: “The interesting findings of this large study are worthy of serious further debate. This study is yet another example of how the NIHR HTA Programme reaches the parts that other research funders may not tackle.”

The study was conducted by a consortium of 25 investigators from 21 institutions worldwide. For more information on this study visit the NIHR Journals Library website. 

  • Summary:
    Vitamin D supplements have been found to protect against acute respiratory infections including colds, flu and pneumonia, according to a study funded by the NIHR.
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