Vitamin D deficiency as a risk factor for childhood allergic disease and asthma

Abstract

Purpose of review: Over the past 2 years, the number of studies relating vitamin D deficiency and asthma and allergies has increased significantly. The purpose of this review is to update the last review in this journal and examine the evidence of the relationship between vitamin D deficiency and childhood asthma and allergies.

Recent findings: In the past 2 years since the last review, there have been many studies, both cross-sectional and prospective, that have investigated the effects of vitamin D on the inception and severity of asthma and allergies. Most, but not all, studies have shown that low vitamin D levels increase the risk for asthma and allergies, but a few suggest an increased risk with high levels. Results from small trials of short duration suggest that vitamin D supplementation decreases severity of eczema and decreases the risk for asthma exacerbations.

Summary: Data that vitamin D deficiency results in increased risks for asthma and allergies continues to accumulate. However, the optimal level of vitamin D that decreases both the risk for development and severity of these disorders remains elusive. Results of ongoing clinical trials of vitamin D supplementation will be needed before recommendations can be firmly established.

Figure 1

Mechanisms of vitamin D in asthma and allergy development. Vitamin D has both in utero and postnatal effects that may affect the development of asthma and allergies. In the in utero period, vitamin D has been shown to play a role in lung growth and maturation. It is likely that this effect is also operating in the postnatal period. Vitamin D has effects on the developing immune system, specifically the development of Tregulatory cells and dendritic cells. The net effect of this is believed to be a balance between Th1 and Th2 responses, suppression of Th17 responses, and ultimately a decrease in sensitization. Vitamin D is also know to be critical to innate immune responses, specifically in this case, to respiratory viral infections. It has been shown that vitamin D dampens the inflammation that occurs after respiratory viral infections such as respiratory syncitial virus infections. This could lead to decreased adverse sequelae of these infections and lead to improved lung function and decreased airway responsiveness. Modified extensively from previous work: CML – Respiratory Medicine 2010;24(1):1–9.

Figure 2

Mechanisms of vitamin D in decreasing the risk for asthma exacerbations. Many of the mechanisms that are mediated by vitamin D to prevent asthma are likely operating to prevent disease exacerbations. In addition to the effects of vitamin D in improving handling of respiratory infections, improve immune cell function, decreasing inflammation, prevention of airway smooth muscle over proliferation, vitamin D has also been shown to improve the response to steroids in asthma by reversing the steroid resistant state through upregulation of IL10 production. Modified extensively from previous work: CML – Respiratory Medicine 2010;24(1):1–9.