Sunlight, blood sugar and diabetes: a new study finds an intriguing connection

News-Medical reports on a study published in *Scientific Reports* that examined whether sunlight exposure is associated with blood glucose levels and type 2 diabetes risk. Researchers from the University of Edinburgh and Karolinska Institute used UK Biobank data collected from 2006 to 2010, combining participants’ health information with ultraviolet A exposure estimates from the Japan Aerospace Exploration Agency. They analyzed short-term ambient UVA exposure near participants’ homes and compared it with blood glucose levels, while also using reported solarium or sunlamp use as a proxy for longer-term sunlight-seeking behavior.

The study found that higher short-term UVA exposure was associated with modestly lower blood glucose, especially in winter. A two-day UVA average ending on the day of blood sampling was linked with lower glucose in winter, while a seven-day average was linked with lower glucose in both winter and spring. In a separate retrospective analysis limited to White European participants, occasional solarium users had a 14% lower hazard of type 2 diabetes than non-users, and frequent users had a 22% lower hazard. More frequent solarium use was also associated with lower predicted BMI and blood glucose and higher vitamin D levels.

The findings are potentially relevant because type 2 diabetes is a major public-health burden, and previous research has linked low vitamin D with diabetes risk without proving that vitamin D supplementation prevents the disease. The authors suggest sunlight may influence metabolism through vitamin D-independent pathways, possibly involving nitric oxide released from the skin after UV exposure, which may affect blood flow, insulin secretion, and insulin sensitivity. However, the researchers stressed that the study is observational and does not prove causation. Ambient UVA is an imperfect measure of personal sun exposure, glucose testing was not standardized for fasting, and solarium use and diabetes history were self-reported. The article also notes that sun exposure and solarium use carry skin-cancer risks, so the findings should guide further research rather than encourage solarium use as a diabetes-prevention strategy.