Vitamin D supplements reduce asthma flare-ups that require treatment with systemic corticosteroids, regardless of patients’ age, ethnicity, body-mass index, use of inhaled corticoids, or vitamin D levels before starting supplements, a study shows.

Asthma exacerbations, which include shortness of breath, coughing, wheezing and tightness in the chest, have been linked to vitamin D deficiency. Studies have shown that the supplements reduce the risk of the flare-ups. But it was unclear whether the reduction works only in patients with a low level of vitamin D to start with.

A research team decided to look for a connection between patients’ levels of vitamin D before starting supplements and the supplements’ effect on asthma flare-ups. Their study, “Vitamin D supplementation to prevent asthma exacerbations: a systematic review and meta-analysis of individual participant data,” was published in the journal The Lancet Respiratory Medicine.

The scientists combed through several research databases and the Cochrane central register of controlled trials for studies on vitamin D supplements in asthma patients who experiences flare-ups.

Seven of the 483 studies were randomized, controlled trials, so they chose them for their analysis. The seven covered 955 participants.

The team divided participants into several groups. One group had low levels of vitamin D before starting supplements, and another high levels. Other groups were based on age, ethnicity, body-mass index, use of inhaled corticoids, and vitamin D levels at the end of the studies.

Researchers assessed the effectiveness of vitamin D supplementation by looking at the number of patients’ asthma flare-ups that required systemic corticosteroid therapy.

All of the participants who took vitamin D supplements had fewer asthma exacerbations requiring systemic corticosteroids, the team discovered. Another finding was that the supplements’ effect was the same across the subgroups, with no group benefiting more than another.

“Vitamin D supplementation reduced the rate of asthma exacerbations requiring treatment with systemic corticosteroids overall,” the team wrote. “We did not find definitive evidence that effects of this intervention differed across subgroups of patients.”