Sun Exposure and Its Effects on Human Health: Mechanisms through Which Sun Exposure Could Reduce the Risk of Developing Obesity and Cardiometabolic Dysfunction

Abstract

Obesity is a significant burden on global healthcare due to its high prevalence and associations with chronic health conditions. In our animal studies, ongoing exposure to low dose ultraviolet radiation (UVR, found in sunlight) reduced weight gain and the development of signs of cardiometabolic dysfunction in mice fed a high fat diet. These observations suggest that regular exposure to safe levels of sunlight could be an effective means of reducing the burden of obesity. However, there is limited knowledge around the nature of associations between sun exposure and the development of obesity and cardiometabolic dysfunction, and we do not know if sun exposure (independent of outdoor activity) affects the metabolic processes that determine obesity in humans. In addition, excessive sun exposure has strong associations with a number of negative health consequences such as skin cancer. This means it is very important to “get the balance right” to ensure that we receive benefits without increasing harm. In this review, we detail the evidence around the cardiometabolic protective effects of UVR and suggest mechanistic pathways through which UVR could be beneficial.

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

“…7 Other reports suggest that nbUVB therapy modifies the skin microbiome with these changes linked to the capacity of this therapy to control psoriatic flare. 8 In addition, pre-clinical [9][10][11] and human studies [12][13][14] indicate that UVR may be beneficial for metabolic health. Adult mice fed a high fat diet and exposed repeatedly to sub-erythemal (non-burning) UVB (1 kJ/m 2 ) over 12 weeks gained less weight, exhibited reduced metabolic dysfunction (e.g.…”

Sub-erythemal ultraviolet radiation reduces metabolic dysfunction in already overweight mice

“…small sample size), the initial vitamin D status of participants (e.g. not being vitamin D-deficient at the start of the trial) and the amount and timing of vitamin D supplementation; however, the biological activity of non-vitamin D sun-induced mediators like nitric oxide (Feelisch et al 2014, Liu et al 2014, Fleury et al 2016 may also explain the lack of effects observed.…”

Exploring the Role of Vitamin D. Comments on Fleury et al. Sun Exposure and Its Effects on Human Health: Mechanisms through Which Sun Exposure Could Reduce the Risk of Developing Obesity and Cardiometabolic Dysfunction. Int. J. Environ. Res. Public Health 2016, 13, 999

“…The mechanistic data presented in this interesting review suggests that long-term exposure to safe levels of ultra-violet radiation (UVR) has protective effects against the development of obesity and cardiovascular dysfunction beyond those induced by the cutaneous synthesis of vitamin D3 through factors such as the induction of cutaneous NO secretion [1]. Evidence from studies achieving comparable vitamin D status (serum 25-hydroxyvitamin D (25OHD) concentrations) is quoted [2], where features of metabolic syndrome were better suppressed by the UVR doses used than by supplementation.…”