Study finds vitamin D supplements cut respiratory infections but public health officials not convinced
Results from a meta-analysis involving 11,321 people show that those given vitamin D supplementation were less likely to experience an acute respiratory infection.
A meta-analysis has found that vitamin D supplementation can cut the risk of respiratory infections, but Public Health England (PHE) does not think it provides sufficient evidence to back the use of the nutrient to reduce these types of infections.
The researchers, who studied data on 11,321 individuals from 25 randomised controlled trials of vitamin D supplementation, found an overall reduction of around 12% in the odds of people experiencing at least one acute respiratory infection with vitamin D supplementation.
The effect was greatest in those who had low vitamin D levels before starting supplements and in those who received daily or weekly supplementation, rather than more widely spaced bolus doses.
“This major collaborative research effort has yielded the first definitive evidence that vitamin D really does protect against respiratory infections,” says lead author Adrian Martineau from Queen Mary University of London.
However, Louis Levy, head of nutrition science at PHE, says: “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.”
Current advice from PHE states that people should consider taking daily 10μg vitamin D during the autumn and winter months, or year-round for those at high-risk of deficiency, for its protective effects on musculoskeletal health (see below).
Vitamin D advice from Public Health England:
- In spring and summer, the majority of the population get enough vitamin D through sunlight on the skin and a healthy, balanced diet. During autumn and winter months, everyone will need to rely on dietary sources of vitamin D. Since it is difficult for people to meet the 10μg recommendation from consuming foods naturally containing or fortified with vitamin D, people should consider taking a daily supplement containing 10 micrograms of vitamin D in autumn and winter months.
- People whose skin has little or no exposure to the sun, like those in institutions such as care homes, or who always cover their skin when outside, risk vitamin D deficiency and need to take a supplement throughout the year. Ethnic minority groups with dark skin, from African, Afro-Caribbean and South Asian backgrounds, may not get enough vitamin D from sunlight in the summer and therefore should consider taking a supplement all year round.
- Children aged one to four years should have a daily 10μg vitamin D supplement. Public Health England also recommends that babies are exclusively breastfed until around six months of age. As a precaution, all babies under one year should have a daily 8.5-10μg vitamin D supplement to ensure they get enough. Children who have more than 500ml of infant formula a day do not need any additional vitamin D as formula is already fortified.
Published in The BMJ (online, 15 February 2017), the meta-analysis looked at vitamin D supplementation ranging from 7 weeks to 18 months in duration.
The researchers found that, overall, 33 people needed to receive vitamin D supplementation to prevent one case of acute respiratory tract infection. In patients who received daily or weekly vitamin D without additional bolus doses, the number of patients needed to treat was lower at 20.
When the researchers looked only at people who were profoundly vitamin D-deficient (serum 25-hydroxyvitamin D level of less than 25 nmol/L) and received daily or weekly supplementation, only four people needed to be treated to prevent one acute respiratory tract infection.
They also report that vitamin D supplementation was not associated with an increased odds of experiencing an adverse event.
The researchers say their study supports a major new indication for vitamin D supplementation in the prevention of respiratory infections and the evidence provides support for routinely adding the vitamin to foodstuffs in this country.
“Vitamin D fortification of foods provides a steady, low-level intake of vitamin D that has virtually eliminated profound vitamin D deficiency in several countries,” they explain.
“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.”
But in an accompanying editorial, also published in The BMJ (online, 15 February 2017), Mark Bolland from the University of Auckland, and Alison Avenell, clinical chair of health services research at the University of Aberdeen, argue that the findings of the meta-analysis are not strong enough to change clinical practice.
They suggest that the definition of respiratory tract infection used in the study was too broad — including patient-reported colds, radiograph-confirmed pneumonia and acute otitis media — and that the results are too heterogenous to be applicable to the general population.
They also note that the absolute reduction in infections reported in the study equates to only 2%, from 42% of people experiencing an acute respiratory infection to 40%.
Current evidence does not support routine vitamin D supplementation, they say, except in people at high risk of osteomalacia, reflected by a serum 25-hydroxyvitamin D level of less than 25 nmol/L.
“The only proven musculoskeletal benefits are for protection against osteomalacia and rickets — vitamin D on its own does not protect against fractures,” says Avenell.
She adds that taking long-term, high-dose daily vitamin D over 4,000IU/d is unwise, but this dose is ten times that often recommended.
“Over-supplementation with vitamin D increases the blood calcium level, and this is associated with kidney stones, constipation, stomach ulcers, psychological changes, and heart rhythm disorders.
“We don’t think people will be interested in taking vitamin D long term for a 2% reduction in upper respiratory tract infections, but there should be no harm if they do.”
Citation: The Salvadore DOI: 10.1211/PJ.2017.20202362
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