Clinical Data Conflict on Vitamin D and Asthma

Asthma’s increasingly deleterious morbidity and socioeconomic burden are of tremendous concern to clinicians and public health officials, spurring efforts to uncover modifiable environmental and nutritional factors that could lessen the disease’s impact.

Several clinical trials have been conducted to test the role of vitamin D deficiency in the current asthma epidemic, and researchers recently examined this relationship in the August 2015 issue of Current Opinion in Allergy and Clinical Immunology.

Vitamin D deficiency has been associated with increased airway reactivity, reduced lung function, and worse asthma control. Vitamin D has prominent immunomodulatory functions that influence immune effector cell activities, thereby reducing inflammatory responses induced by respiratory viral infections.

Many observational studies have examined the relationship between low vitamin D levels and asthma, but the findings are mixed. The researchers attributed these incongruent conclusions to asthma’s heterogeneous nature and confounding variables among population-based studies.

Epidemiologic studies, which do not provide the best or ideal quality evidence, have linked vitamin D insufficiency or deficiency to increased asthma morbidity, prompting the hypothesis that vitamin D supplementation could improve asthma control.

Investigators have structured and initiated several controlled clinical trials that provide better evidence to explore the effect of vitamin D supplementation on asthma control and respiratory tract infections.

Some trials have shown that vitamin D supplementation in children reduces asthma severity, which also seems to suggest that the supplements could potentiate the effect of corticosteroids. However, similar trials in adults have shown no beneficial role.

Clinicians should not recommend vitamin D replacement routinely as an adjunctive therapy for asthma, the researchers maintained. Clinical studies that examined long-term supplementation over several seasons are needed, since humans derive most of their vitamin D from sun exposure.