Systematic Review of the Effects of Ultraviolet Radiation on Markers of Metabolic Dysfunction

Emerging findings suggest that exposure to ultraviolet wavelengths of sunlight modulates metabolic function. Here we review the metabolic effects of exposure to ultraviolet radiation (UVR), focusing on the effects of phototherapies (that administer UVR), and advice to increase sun exposure in individuals enrolled in clinical trials and intervention studies. We identified 25 studies in which the effects of UVR on metabolic outcomes were examined, including: narrowband ultraviolet B phototherapy (nbUVB, n = 12); psoralen ultraviolet A phototherapy (n = 4); other types of UVR phototherapy (n = 5); and sun exposure advice (n = 5). Most studies recruited a small number of participants (≤100), who were middle-aged individuals undergoing treatment for psoriasis flare, with phototherapy or sun exposure advice administered for ≤12 weeks. Data obtained at baseline were usually compared with an endpoint following treatment with UVR, for a limited number of outcomes. There were few studies in which markers of glucose metabolism were assessed, with some beneficial effects of sun exposure (but not phototherapy) reported. LDL-cholesterol levels were lower in individuals receiving sun exposure advice, while treatment with nbUVB reduced blood concentrations of inflammatory markers (C-reactive protein and interleukin-6). Future studies should focus on determining whether the effects of these interventions change with time, and if they are dependent on the source of UVR (i.e. phototherapy or sun exposure) and wavelength(s) of light administered. Furthermore, studies need to measure a variety of (clinical) markers of glucose metabolism, adiposity and inflammation, control for factors such as skin type and sex, and stratify participants for metabolic disease diagnosis.