GREATER exposure to sunlight may be associated with lower blood glucose levels and a reduced risk of Type 2 diabetes, according to a large UK study.
Researchers analysing data from more than 400,000 UK Biobank participants found that short-term sunlight exposure was associated with modest reductions in blood glucose, while a measure of longer-term sun exposure was linked to a lower likelihood of Type 2 diabetes.
The researchers examined data from 429,368 UK Biobank participants, comparing blood glucose measurements with levels of ultraviolet A (UVA) radiation around participants’ homes during the two and seven days before their assessment.
Sunlight exposure was estimated using satellite data, while the analysis accounted for factors including temperature, season, day of the week, and longer-term trends.
It was found that during winter, each 1 W/m² increase in average UVA exposure over the previous two days was associated with a 0.015 mmol/L reduction in blood glucose. For seven-day exposure, glucose was 0.027 mmol/L lower for each 1 W/m² increase. A smaller association was also observed during spring.
The relationship, however, was not linear. Researchers found that glucose levels fell most sharply when sunlight exposure increased from very low levels, before reaching a plateau at higher exposure. This could help explain why the strongest associations were seen during winter, when overall sunlight levels are lower.
The study also investigated longer-term exposure using reported sun-bed use as an indicator of habitual sun exposure.
Among 408,531 participants, 16,971 had been diagnosed with diabetes. After adjusting for factors including BMI, smoking, physical activity, education, employment, deprivation, and mental health, occasional sun-bed users were found to have a 14% lower hazard of Type 2 diabetes compared with non-users.
Frequent users had an even lower hazard at 22%. Frequent users also had higher vitamin D levels and slightly lower BMI and blood glucose levels,
However, the researchers emphasised that these results should not be interpreted as evidence supporting sunbed use, which carries established health risks including increasing the risk of dangerous skin cancers like melanoma.
Instead, sunbed use may be a marker of greater overall sunlight exposure, as people who use sunbeds may also be more likely to seek out the sun regularly.
The findings raise the possibility that sunlight could influence metabolic health through mechanisms beyond vitamin D.
The authors highlighted nitric oxide, which is released from stores in the skin following UV exposure and may improve blood flow, insulin secretion, and insulin sensitivity. Red and near-infrared wavelengths in sunlight may also affect mitochondrial energy production.
Importantly, the study was observational and cannot establish that sunlight directly prevents Type 2 diabetes. Ambient UVA was also used as a proxy for personal sunlight exposure, meaning researchers could not determine how much time individual participants actually spent outdoors.
The authors conclude that clinical studies are now needed to investigate the mechanisms involved and determine whether there are safe, optimal levels of sunlight exposure that could support metabolic health.
Reference
Stevenson A C et al. Sunlight exposure is associated with lower blood glucose levels and type 2 diabetes. Sci Rep (2026). https://doi.org/10.1038/s41598-026-66100-4
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