Taking high-dose vitamin D supplements does not reduce a healthy adult’s risk of developing an upper respiratory tract infection, according to a study published in JAMA today.
Several lines of evidence have linked lower levels of vitamin D in the body with susceptibility to infections. Some observational studies, for example, have suggested that individuals with lower levels of the vitamin are at higher risk of developing infections, including tuberculosis. But observational studies can’t prove whether low vitamin D levels cause individuals to become infected more easily; they can only indicate an association exists. Other evidence suggests that vitamin D plays an important role in the human immune response. In particular, vitamin D is believed to have a role in the production of immune cells called cathelicidins, which are believed to act as antimicrobial agents in the immune system.
To determine whether vitamin D supplementation can help prevent respiratory infections, a team of researchers from New Zealand conducted a clinical trial comparing the frequency and severity of respiratory infections among 322 healthy adults without a vitamin D deficiency who were randomized to receive high doses of vitamin D or a placebo. Individuals in the vitamin D group and those in the placebo group experienced about the same number of infections—3.7 vs 3.8 per person over the 18-month course of the study, respectively. There also was no difference in the number of workdays missed, the duration of cold symptoms, or the severity of illness between the 2 groups.
Lead author David Murdoch, MD, head of pathology at the University of Otago in Dunedin, New Zealand, discussed the findings with news@JAMA.
news@JAMA: How does your study advance our understanding of vitamin D supplementation’s effect on respiratory illness?
Dr Murdoch: It is now clear that vitamin D supplements do not prevent or reduce the severity of colds in adults without a frank vitamin D deficiency.
news@JAMA: Does this end the debate about the value of vitamin D supplementation in the prevention of respiratory infections?
Dr Murdoch: No. We still do not know whether colds can be prevented in those with a vitamin D deficiency. We also do not know whether vitamin D supplementation will prevent or reduce the severity of influenza.
news@JAMA: Are there any risks of vitamin D supplementation for healthy individuals?
Dr Murdoch: Like any drug, there are potential side effects, but these are uncommon. There were no adverse events attributed to vitamin D in the study.
news@JAMA: Is there any reason to believe that vitamin D supplementation might prevent respiratory infections in other populations?
Dr Murdoch: Yes. There was a recent study from Mongolia that showed that vitamin D supplementation reduced the incidence of respiratory infections in children with very low baseline vitamin D levels.