Shining theLight onSunshine: a systematic review of the influence of sun exposure on type 2 diabetes mellitus‐related outcomes

Abstract

SummaryProspective observational studies uniformly link vitamin D deficiency with the incidence of type 2 diabetes mellitus (T2DM), yet trials supplementing participants at risk of T2DM with vitamin D to reduce progression to T2DM have yielded inconsistent results. Inconsistencies between supplementation trials may be due to insufficient dosing or small sample sizes. Observational studies may also have reported spurious associations due to uncontrolled confounding by lifestyle or genetic factors. Alternatively, observational and intervention studies may not be entirely comparable. Observational studies show an association between higher vitamin D status, which is predominantly derived from sun exposure, and decreased incidence of T2DM. Trials intervene with vitamin D supplementation, and therefore may be missing alternate causes of the effect of sun exposure, as seen in observational studies. We propose that sun exposure may be the driving force behind the associations seen in observational studies; sun exposure may have additional benefits beyond increasing serum 25-hydroxyvitamin D (25OHD) levels. We performed an electronic literature search to identify articles that examined associations between sun exposure and T2DM and/or glucose metabolism. A best evidence synthesis was then conducted using outcomes from analyses deemed to have high methodological quality. Ten eligible full-text articles were identified, yielding 19 T2DM-related outcomes. The best evidence analysis considered 11 outcomes which were grouped into six outcome types: T2DM, fasting glucose, glucose tolerance, fasting insulin, insulin secretion and insulin sensitivity. There was moderate evidence to support a role of recreational sun exposure in reducing odds of T2DM incidence.High-level evidence was lacking; evidence presented for other outcomes was of low or insufficient level. This review highlights significant gaps in research pertaining to sun exposure and T2DM-related outcomes. Further research is encouraged as we aim to identify novel preventative strategies for T2DM.

Association of Light Exposure on Physical Activity and Sedentary Time in Young People

“…This paper aimed to investigate whether light exposure was associated with objectively measured physical activity and sedentary behaviour. Previous research has suggested that greater light exposure is associated with more favourable health outcomes in adults [ 8 , 9 , 10 , 11 ]. One study found a positive trend between light exposure and physical activity, although this was only in a small sample of adults [ 31 ].…”

“…One environmental factor that has received little attention so far is light exposure. More light exposure has been found to be associated with several health outcomes, including lower adiposity [ 8 ], reduced levels of depression [ 9 ], reduced risk of type 2 diabetes mellitus [ 10 ] and some cancers [ 11 ]. In addition, seasonal patterns in clinical events have been observed, with better survival rates in the summer [ 12 , 13 ].…”

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

“…In other studies, seasonal increases in adiposity, BMI, abdominal obesity and HbA1c levels have been observed in winter [82,83], although there is uncertainty around seasonal effects on insulin secretion and sensitivity [84,85]. Research in pregnant women suggests that increased sun exposure around the time of delivery was associated with a reduced risk of gestational hypertension [86].…”

Ultraviolet radiation, vitamin D and the development of obesity, metabolic syndrome and type-2 diabetes

“…however, evidence around the seasonal effects on insulin secretion and sensitivity is inconclusive (reviewed by 83 ).…”