Objective: To review the current literature on vitamin D and asthma, discussing the possible roles of vitamin D on asthma pathogenesis and the potential consequences of vitamin D deficiency.
Data Sources: PubMed database was searched from 1950 to 2009. Keywords used included asthma, vitamin D, inflammation, airway smooth muscle and cytokines.
Study Selection: Articles were selected based on relevance to the subject.
Vitamin D deficiency has been associated with epidemiologic patterns observed in the asthma epidemic. Vitamin D deficiency is more common with obesity, African American ethnicity, and westernization of countries with higher-risk populations for asthma.
Evidence suggests that:
• Vitamin D deficiency is associated with increased airway hyper-responsiveness, lower pulmonary functions, worse asthma control, and possibly steroid resistance.
• Lung epithelial cells express high baseline levels of 1alpha-hydroxylase. This allows the conversion of inactive calcidiol [prehormone the body makes from naturally occuring D3] to active calcitriol locally within the lung. Calcitriol has been shown to inhibit the synthesis and release of certain cytokines, such as RANTES, platelet-derived growth factor, and matrix metalloproteinases, from bronchial smooth muscle cells, thereby leading to decreased lung inflammation and smooth muscle cell proliferation.
• Vitamin D also increases synthesis of interleukin 10 [an anti-inflammatory cytokine] by CD4+CD25+Foxp3+ T-regulatory cells and dendritic cells,
• While concurrently inhibiting dendritic cell activation by downregulating expression of costimulatory molecules CD40 and CD80/86.
• Vitamin D is also capable of inducing the expression of several anti-infective molecules, such as cathelicidin.
Thus, vitamin D has a number of biologic effects that are likely important in regulating key mechanisms in asthma.
Conclusions: We hypothesize that vitamin D supplementation may lead to improved asthma control by inhibiting the influx of inflammatory cytokines in the lung and increasing the secretion of interleukin 10 by T-regulatory cells and dendritic cells.
Source: American College of Allergy, Asthma and Immunology news release, Sep 8, 2010 [Email: firstname.lastname@example.org]