Rx: A Little Sunshine Without Sunscreen?

Exposing our skin to the sun for 20 to 30 minutes per day can result in the production of more than five times the recommended daily allowance of vitamin D. Yet because of differences in lifestyle and sunscreen use, people in the sunniest cities are reported to have the lowest blood levels of this vitamin. The physiologically active metabolite of vitamin D—the hormone calcitriol—exerts its effects by binding to receptors in the nuclei of target cells found throughout the body, modulating the expression of thousands of genes. Vitamin D deficiency is a factor in the pathology of cancers, diabetes, and heart, bone, muscle, neuronal, and autoimmune diseases. Now, Sutherland et al . provide evidence that decreased blood levels of vitamin D are related to asthma severity. Adult asthma patients with low blood levels of vitamin D showed poor lung function, increased airway hyperresponsiveness (airway spasms or constrictions), and decreased responses to inhaled steroid treatment relative to those with higher levels. This decreased response to steroids was associated with reduced induction of mitogen-activated protein kinase phosphatase, which ultimately caused persistent increased proinflammatory cytokine production. Reduced vitamin D levels were also associated with increased body mass index, further supporting obesity as a risk factor for asthma. This study adds to our understanding of the existing variability among asthma patients’ response to inhaled steroid treatment. These findings also might reflect vitamin D availability as another factor that could contribute to the protection against allergies and asthma that is seen in rural populations, a fact that has intrigued researchers for a long time. More importantly, this study provides a basis for the use of supplemental vitamin D (or more sun exposure) to improve asthma symptoms. E. R. Sutherland et al ., Vitamin D levels, lung function, and steroid response in adult asthma. Am. J. Respir. Crit. Care Med. 181 , 699–704 (2010). [[Abstract]][1] [1]: http://ajrccm.atsjournals.org/cgi/content/abstract/181/7/699