Sunlight and Vitamin D: Necessary for Public Health

Abstract

The World Health Organization's International Agency for Research on Cancer recommends avoiding outdoor activities at midday, wearing clothing to cover the whole body, and daily use of sunscreen on usually exposed skin [1]. The American Cancer Society advocates Slip! Slop! Slap! and Wrap! to make sure skin is covered in clothing or sunscreen and to avoid exposure to the sun between 10 am and 4 pm [2]. The U.S. Surgeon General has issued a Call to Action focused on reducing ultraviolet (UV) exposure, whether from indoor UV or from the sun [3]. Though these recommendations, all focused on reduction of skin cancer, are accompanied by brief acknowledgement of the importance of vitamin D for health, they persist in urging avoidance of the sun at the precise times when vitamin D can be synthesized in the skin—the hours between 10 am and 3 pm—and suggest that all necessary vitamin D can be obtained through food and dietary supplements. These recommendations are understandable from the viewpoint of preventing the 3.5 million new cases of and 2000 deaths from nonmelanoma skin cancer in the United States each year [4], but they neglect the fact that we have a long cultural history of appreciation of the sun and use of UV radiation for healing purposes. Moreover, they neglect that we have evolved with physiological adaptations to help protect the skin from the sun [5] when we are mindful of our exposure and do not burn. They neglect the fact that increased sun exposure, based on latitude, has been associated with protection from several different types of cancer [6–15], type 1 diabetes [16], multiple sclerosis [17,18], and other diseases [19–23]. They also neglect the fact that exposure to the sun induces beneficial physiological changes beyond the production of vitamin D. Though adherence to the current sun-protective recommendations would likely result in the reduction of nonmelanoma skin cancer, that reduction would likely be overshadowed by the potential reduction in deaths from other cancers and from cardiovascular disease, which could be achieved by doubling average blood concentrations of 25-hydroxyvitamin D (25(OH)D) to 40 ng/mL through a combination of sun exposure and supplements [24]. The potential harm of sun avoidance and the neglect of its positive effects on human health led to a seminar, Vitamin D for Public Health: Integrating Sunshine, Supplements and Measurement for Optimal Health, presented by GrassrootsHealth at the University of California San Diego to inform and to help initiate an action plan to restore a more balanced approach to solar radiation based on input by the conference speakers.