Academics divided over vitamin D study claims of cold and flu protection

By Gary Scattergood contact

- Last updated on GMT

The study aimed to assess the overall effect of vitamin D supplements on risk of acute respiratory tract infection. © iStock
The study aimed to assess the overall effect of vitamin D supplements on risk of acute respiratory tract infection. © iStock
Vitamin D supplements could help prevent acute respiratory tract infections, including colds and flu, according to a study in The BMJ. But a linked editorial penned by academics from New Zealand and Scotland argues the results are “not sufficiently applicable to the general population.”

Led by researchers from Queen Mary University of London, the BMJ study recommends “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.”

But others say a clinically useful effect remains uncertain and needs confirmation.

In a linked editorial, Mark Bolland from the University of Auckland and Alison Avenell from the University of Aberdeen, who recently questioned the evidence for use of vitamin D supplements to prevent disease, say a clinically useful effect remains uncertain and requires confirmation in well-designed adequately powered randomised controlled trials.

The study assessed the overall effect of vitamin D supplements on risk of acute respiratory tract infection in a systematic review and meta-analysis of individual participant data from 25 randomised controlled trials of vitamin D supplementation, involving 11,321 participants aged 0 to 95 years.

They found that vitamin D supplementation resulted in a 12% reduction in the proportion of participants experiencing at least one acute respiratory tract infection.

Our study reports a major new indication for vitamin D supplementation: the prevention of acute respiratory tract infection," ​wrote the authors. "We also show that people who are very deficient in vitamin D and those receiving daily or weekly supplementation without additional bolus doses experienced particular benefit. 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.”

Further analyses among specific groups showed benefits are greater in those receiving daily or weekly vitamin D without additional large doses. They added the protective effects were strongest among those with severe vitamin D deficiency (less than 25 nmol/L baseline blood levels).

Headline view questioned

However, in a linked editorial, Bolland and Avenell question the headline finding of the study – namely the 12% reduction in the odds of an acute respiratory tract infection from supplementation.

“There are reasons for viewing the headline result cautiously,”​ they wrote. “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."

“Furthermore, 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. It is difficult to know whether a reduction in this mixture of conditions is applicable to the general population and how it should be interpreted clinically.”

They concluded that 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 25 nmol/L).”

Commenting on the research, Professor Louis Levy, head of nutrition science at Public Health England, noted that recent recent recommendations from the UK's Scientific Advisory Committee on Nutrition (SACN), suggest that certain population groups should take a daily 10 micrograms Vitamin D supplement year round and that everyone consider taking a supplement during the autumn and winter months to protect musculoskeletal health. 

However, she noted that the evidence on vitamin D and infection is inconsistent "and this study does not provide sufficient evidence to support recommending Vitamin D for reducing the risk of respiratory tract infections.”

In contrast, Dr Benjamin Jacobs, a consultant paediatrician at the Royal National Orthopaedic Hospital in the UK said the study is 'a major step forward' - adding that the BMJ study shows strong evidence of benefit and safety of vitamin D supplements from a rigorous analysis of 25 clinical trials.

“Martineau’s study shows a clear reduction in respiratory infection in people taking vitamin D, including patients of all age groups,"​ said Jacombs. "The main caveat is the finding that vitamin D was only effective if given daily or weekly.  Large doses given once a month, or even less frequently, did not show benefit and may even be harmful."

He added that commentaries from Bolland and other sceptics 'try, but fail, to find weaknesses' in the analysis analysis. 

"Martineau’s data is strong, from 11,000 patients in good quality clinical trials around the world. The case for universal vitamin D supplements, or food fortification with vitamin D, is now undeniable,"​ said Jacobs. "Governments and health professionals need to take Martineau’s study into account when setting Vitamin D policy now.”

Source: The BMJ
“Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data​”
doi: https://doi.org/10.1136/bmj.i6583
Authors: Adrian R Martineau, et al
Linked editorial: BMJ​ 2017; 356 doi: https://doi.org/10.1136/bmj.j456

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