Vitamin D supplements do not reduce the number or severity of colds in asthma patients, according to a new study published online ahead of print publication in the American Thoracic Society's American Journal of Respiratory and Critical Care Medicine.
Loren C. Denlinger, MD, PhD, associate professor of medicine at the University of Wisconsin, and colleagues conducted a randomized, controlled trial of adults with mild-to-moderate asthma. Among African Americans in the study, those receiving supplemental vitamin D, rather than a placebo, experienced more colds.
The findings surprised the researchers who had previously published research showing a 40 percent reduction in asthma exacerbations in patients with a vitamin D deficiency who achieved normal levels of the vitamin with supplements. Because colds often trigger exacerbations, they hypothesized that vitamin D supplementation would reduce colds and cold severity.
"Other studies of vitamin D and colds have produced mixed results," Dr. Denlinger said. "Most of those studies were conducted among healthy patients. We wanted to ask the same question of a patient population in which the impact of a cold carries greater risk."
The researchers followed asthma patients who were undergoing inhaled corticosteroid (ICS) tapering, Denlinger added, to test the hypothesis that vitamin D might bolster the potency of the ICS.
The multi-center AsthmaNet Vitamin D Add-on Therapy Enhances Corticosteroid Responsiveness (VIDA) trial enrolled 408 adults with mild-to-moderate asthma whose vitamin D levels were insufficient or deficient (25-OH-D3 < 30 ng/mL). Those enrolled had asthma symptoms despite low-dose ICS therapy. The patients were randomized to receive either vitamin D supplementation (100,000 IU once, then 4000 IU daily) or placebo for 28 weeks. Neither the patients nor their physicians knew whether they received vitamin D or the placebo.
During that time, about half the participants experienced at least one cold. The severity of their colds was measured by the Wisconsin Upper Respiratory Symptom Survey-21 (WURSS-21).
The researchers analyzed separately the results of the 82 percent of participants receiving supplements who achieved vitamin D sufficiency within 12 weeks. Achieving sufficiency made no difference in number of colds or their severity this group experienced.
The researchers wrote that one possible explanation for the unexpected finding: asthma patients with low vitamin D levels may be more likely to experience upper respiratory infections asymptomatically than those with normal levels of vitamin D, which is known to trigger an inflammatory response. This inflammatory response may, in turn, reduce the risk of lower airway infections, which are triggers for asthma exacerbations.
Although there are other reasons to recommend vitamin D supplements for asthma patients, including the fact that they are at greater risk for bone weakening, Denlinger said, "we can't recommend vitamin D for the prevention of colds."