Taking vitamin D supplements does not reduce the number or severity of colds experienced by asthma patients, according to a US study.
The findings surprised the researchers who in a previous study had found a 40% reduction in asthma exacerbations in patients with a vitamin D deficiency who achieved normal levels with supplements.
“We can’t recommend vitamin D for the prevention of colds”
Because colds often trigger exacerbations, they had hypothesized that vitamin D supplementation would reduce colds and cold severity.
Study author Dr Loren Denlinger, associate professor of medicine at the University of Wisconsin, said: “Other studies of vitamin D and colds have produced mixed results. 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,” she said.
The researchers followed asthma patients who were undergoing inhaled corticosteroid (ICS) “tapering” to test the hypothesis that vitamin D might bolster the potency of the ICS.
The trial involved 408 adults with mild-to-moderate asthma whose vitamin D levels were insufficient or deficient. Study participants had asthma symptoms, despite low-dose ICS therapy.
The patients were randomised to receive either vitamin D supplementation (100,000 IU once, then 4,000 IU daily) or placebo for 28 weeks.
During that time, about half the participants experienced at least one cold, said the study authors in the American Journal of Respiratory and Critical Care Medicine.
The researchers analysed separately the results of the 82% of participants receiving supplements who achieved vitamin D sufficiency within 12 weeks.
Achieving sufficiency made no difference in number of colds or their severity the group experienced, they said.
”In patients with mild-to-moderate asthma undergoing an ICS dose-reduction, these results do not support the use of vitamin D supplementation for the purpose of reducing cold severity or frequency,” they stated in the journal.
“We can’t recommend vitamin D for the prevention of colds,” added Dr Denlinger.
The researchers suggested one explanation for the finding was that 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 – known to trigger an inflammatory response.
The inflammatory response may, in turn, reduce the risk of lower airway infections, which are triggers for asthma exacerbations, they said.