Could Vitamin D Supplements Reduce the Risk of Acute Respiratory Infections?
A recent meta-analysis suggested that vitamin D reduced the risk of acute respiratory infections in patients, with individuals who were vitamin D deficient experiencing the most benefit.1
The study included data from 25 randomized controlled trials and had a total of 11,321 participants between 0 to 95 years of age. Researchers obtained individual participant data for 10,933 patients, and included, age, sex, race or ethnicity, influenza vaccination status, history of asthma or chronic obstructive pulmonary disease (COPD), body mass index (BMI), height, and baseline serum 25-hydroxyvitamin D concentration. Participants within the studies were administered vitamin D orally, and additional bolus dosages were given either daily, weekly or monthly in each of the studies.
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Incidences of acute respiratory infection were assessed, and researchers performed 1 and 2 step meta-analyses on individual patient data for outcomes using random effects models adjusted for age, sex, and study duration. Participant data was divided into subgroups according to baseline vitamin D status, vitamin D dosing regimen, dose size, age, BMI, presence of asthma or COPD, and influenza vaccine status.
Of the 25 trials, baseline serum 25-hydroxyvitamin D concentrations were obtained in 19 studies and the mean baseline concentrations ranged from 18.9 to 88.9 nmol/L.
The researchers’ findings showed that vitamin D supplementation reduced the risk of acute respiratory tract infection in all participants, with an adjusted odds ratio of 0.88. The strongest effects were observed in participants with baseline 25-hydroxyvitamin D concentrations levels below 25 nmol/L compared with those with 25-hydroxyvitamin D concentrations levels of 25 nmol/L or greater.
In addition, the protective effects were seen in subgroups that received daily or weekly vitamin D supplements without additional bolus doses, but not in participants who received 1 or more bolus doses.
“Our study reports a major new indication for vitamin D supplementation: the prevention of acute respiratory tract infection” the researchers concluded, “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.”
The introduction of vitamin D supplements to individuals with deficiencies may be an appropriate public health step. However, Dr Mark J Bolland, associate professor in the Department of Medicine at the University of Auckland, and Dr Alison Avenell, professor in the Health Services Research Unit at University of Aberdeen, caution against the widespread use of vitamin D to prevent acute respiratory infections.
In an accompanying editorial published in the British Medical Journal, the researchers wrote that “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.”2 They also stated that the varied definition of acute respiratory infections between studies would make it difficult to interpret the meta-analysis findings clinically and to determine how applicable the reduction would be in the general public.
“The results are heterogeneous and not sufficiently applicable to the general population. We think that they should be viewed as hypothesis generating only, requiring confirmation in well designed adequately powered randomized controlled trials,” the authors concluded.
—Melissa Weiss
Reference:
1) Martineau AR, Jolliffe DA, Hooper RL, et al. Vitamin D supplementation to prevent actue respiratory tract infections: systematic review and meta-analysis of indivudal participant data [published online February 15, 2017]. BMJ. doi:https://doi.org/10.1136/bmj.i6583.
2) Bolland MJ and Avenell A. Do vitamin D supplements help prevent respiratory tract infections? [published online February 15, 2017]. BMJ. doi:https://doi.org/10.1136/bmj.j456.