The potential role of vitamin D in the link between obesity and asthma severity/control in children

Abstract

Childhood obesity and asthma are major public health problems. Obesity is not only associated with increased risk of incident asthma, but it may worsen asthma severity/control. Although the mechanisms linking obesity with asthma expression have not been completely elucidated, evidence suggests that increased frequency of acute respiratory infection (ARI) and decreased corticosteroid responsiveness may help to explain how obesity worsens asthma expression. In addition, obese individuals have low vitamin D status, and emerging evidence suggests vitamin D affects risk of ARI and corticosteroid responsiveness in individuals with asthma. In this review, we summarize the association between obesity and asthma severity/control in children and discuss ARI and corticosteroid responsiveness as potential mediators in the obesity–asthma pathway. We also discuss the potential role of vitamin D, including a brief summary of recent randomized controlled trials of vitamin D supplementation.

Keywords:

• acute respiratory infection
• asthma
• children
• corticosteroid responsiveness
• obesity
• vitamin D

Financial & competing interests disclosure

C.A. Camargo has done asthma-related consulting for GlaxoSmithKline, Merck, Novartis and Teva and received asthma-related grants from Novartis and Teva. The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.

No writing assistance was utilized in the production of this manuscript.

Key issues

• Childhood obesity and asthma are major public health problems.

• Most studies support that childhood obesity is associated with worse asthma severity and control.

• The mechanistic pathways linking childhood obesity to worse asthma severity/control likely includes both increased risk of acute respiratory infections and decreased corticosteroid responsiveness. However, longitudinal studies disentangling these complex relationships are lacking, and are an important future research direction; interventional studies would be particularly helpful.

• The prevalence of vitamin D deficiency (as defined by low serum 25OHD concentration) increases as weight increases.

• Vitamin D can play a protective role by decreasing T_H1- and T_H2-driven airway inflammation and inflammation caused by acute respiratory infections and by increasing glucocorticoid bioavailability in bronchial smooth muscle cells. Thus, vitamin D deficiency, which is disproportionately high among obese children, may play an important (and modifiable) role.

• While several randomized clinical trials of vitamin D supplementation and risk of ARI among individuals with low vitamin D status have suggested a protective effect of vitamin D supplementation, controversy remains about the role of vitamin D supplementation in improving asthma severity/control, as well as the optimal dose, frequency and duration of supplementation.

• Future research should investigate the role of daily or weekly vitamin D3 supplementation for improving asthma severity/control among obese children with low vitamin D status.

• While vitamin D supplementation might be an effective supplemental therapy for this sub-population of obese children with asthma and low vitamin D status, weight loss programs should also be pursued since the mechanisms for the obesity–asthma relation is undoubtedly multifactorial.