Daylight Exposure Linked to 20% Lower Diabetes Risk in Large Study
A UK analysis of 420,000 people found that sunnier weather in the days prior to testing was associated with lower blood glucose levels.
By Priya Marino ·
More than 420,000 people in the United Kingdom were analyzed in an August study that linked greater sunlight exposure to lower blood sugar levels. The findings suggest a measurable metabolic benefit from natural light that extends beyond vitamin D production and mood regulation.
The researchers used blood-glucose test results from the UK Biobank, a large biomedical database, combined with satellite estimates of sunlight in participants' living areas. They examined whether sunlight exposure in the two days or seven days before a blood test influenced glucose readings. Study co-author Chris Dibben, a health geographer at the University of Edinburgh, noted that blood glucose was lower if participants had recently experienced sunnier weather relative to the time of year.
The effect was most pronounced during winter months. Dibben stated that it makes sense the impact is biggest in the most sunlight-starved time of the year. In a separate analysis using the same medical records, the team found that people who frequently used tanning beds had a roughly 20% reduced lifetime risk of developing Type 2 diabetes compared to non-users. The researchers used tanning bed use as a proxy for higher sun exposure, noting that such users also tend to spend more time sunbathing.
Patrick Schrauwen, a senior scientist at the German Diabetes Center in Düsseldorf, co-authored a smaller experimental study published in the January issue of Cell Metabolism. In that study, 13 people with Type 2 diabetes spent several working days in environments with either natural daylight through windows or only artificial lighting from 8 a.m. to 5 p.m. Continuous glucose monitoring showed that participants spent more time in the normal blood sugar range when they had access to daylight. Schrauwen called it one of the first experimental studies to show that natural light has this effect.
Frank A.J.L. Scheer, a neuroscientist at Harvard Medical School who heads the Medical Chronobiology Program at Mass General Brigham, said the combination of these studies supports the notion that light is important for metabolic and cardiovascular health. He explained that light is the most important signal for the body's circadian system, which helps regulate blood sugar and body weight. Scheer noted that too much light at night can disturb this system, potentially causing blood sugar levels to increase by activating the sympathetic nervous system.
Researchers believe other biological pathways are also involved. Laboratory experiments indicate that exposure to UVA triggers nitrite stores in the skin to turn into nitric oxide. This process widens blood vessels, which could lower blood pressure and improve glucose regulation. As evenings darken earlier in the year, Dibben said the research supports getting outside when possible. Scheer advised people to position themselves near a window if they cannot go outdoors and to cut down on artificial light in the hours before sleep.
