Photochemistry and Photobiology, 2005, 81: 1261–1266 Symposium-in-Print UV Radiation, Vitamin D and Human Health: An Unfolding Controversy Ultraviolet Radiation Exposure, Vitamin D, and Cancer

This paper reviews briefly the evidence for an association between various measures of UV radiation (UVR) exposure and the development of cancer. Issues such as data quality, study design, measurement variation, comparability of studies, and quantification of UV exposure in relation to skin cancer are discussed. A range of exposure, based on skin type, might be appropriate: from 5 min a day three times a week for lightskinned individuals and 10 min a day three times a week for darker-skinned individuals. These exposures translate into 13 h per year, for a light-skinned individual, leading to 650 h of exposure from birth to age 50. UV EXPOSURE AND CANCER Many ecologic, cohort and case control studies have shown that as ground level UV radiation (UVR) increases, cancer mortality and in some cases cancer incidence decreases (1–4). Prostate, colorectal and breast are most studied, although new data have shown that non-Hodgkin lymphoma (5,6) is also inversely associated with sun exposure and that survival with melanoma (4) is inversely associated with sun exposure. The major reason propounded for an association of sun exposure with a protective effect in the development of cancer and improved survival is that vitamin D synthesis is a critical component of cellular networks that inhibit cellular proliferation and encourage apoptosis (7). Therefore research has focused on measures of sun exposure, serum vitamin D levels (and associated metabolites), and genetic variants that may affect vitamin D synthesis. Few studies have combined all three measures, so that this review will not be able to provide integrated information that might be useful for validating the hypothesis. However, each component can be assessed. The purpose of this review is to evaluate the quality of the evidence for health benefits of UVR-induced vitamin D in relationship to the risks of exposure to UVR-induced skin cancer.