Something as simple as sitting by a window in natural light may help people with Type 2 diabetes keep their blood sugar levels more stable, a recent study suggests.
The findings reveal that participants kept their blood sugar within a healthy range 50 percent of the time when exposed to natural light, compared to 43 percent during an artificial-light phase.
“In people exposed to natural light, blood glucose levels were in the normal range for more hours per day, with less variability,” study author Patrick Schrauwen, a scientist at German Diabetes Center, said in a statement. “Two important elements that indicate that our volunteers with diabetes managed to control their sugar levels better.”
Better Blood Sugar Control With Daylight
The study, published in the journal Cell Metabolism, suggests that spending time in natural sunlight could be a helpful addition to blood sugar-control strategies for people with Type 2 diabetes.
Researchers recruited 13 people to test how their office environment affected their health. All participants were assigned to the same office building, but one group was seated at desks with large south- and west-facing windows, maximizing daily sunlight exposure. The other group was placed in rooms fully shuttered from natural light and exposed only to artificial lighting.
Participants sat at their desks from 8 a.m. to 5 p.m., mimicking the typical hours of a 9-to-5 office job.
After a break of at least four weeks, participants returned for a second session. This time, those who were in the artificial-light setting switched to the natural-light office environment, and vice versa. All participants had Type 2 diabetes, did not wear sunscreen during the study period, and had an average age of 70 years.
“Apart from the light source, all other lifestyle parameters—meals, sleep, physical activity, screen time, etc.—were kept strictly identical,” Joris Hoeks, study co-author, said in a statement.
Researchers found that when participants spent time exposed to natural light through a window, they maintained their blood sugar within a healthy range more often than when they were in a room with artificial light. Glucose swings over 24 hours were smaller with natural light, and smaller swings were linked to more time spent in the normal range, suggesting smoother glucose control.
Over the course of the day, people burned more fat and less carbohydrate under natural light—both during quiet rest on day four and after a mixed‑meal test on day five—even though total energy expenditure stayed similar.
Participants’ melatonin levels were also slightly higher in the evening, and their fat-burning metabolism showed improvement.
Why Daylight Might Matter
The study did not establish exactly why sunlight influences blood sugar control, but experts have several theories centered on how light affects the body’s internal biological systems.
“It has been known for several years that the disruption of circadian rhythms plays a major role in the development of metabolic disorders that affect an increasing proportion of the Western population,” Charna Dibner, study co-author and an associate professor at the UNIGE Faculty of Medicine, said in a statement.
Natural light is more effective in synchronizing the body’s biological clock with the environment than artificial lighting, which has a lower light intensity and a narrower wavelength spectrum, Joris Hoeks, study co-author and an associate professor at Maastricht University, said in a statement.
Yet we largely spend our days under artificial lighting, he said.
Other experts suggest that the effect may be related to vitamin D exposure or to the way light-sensitive cells in the eyes help regulate metabolism.
Vitamin D plays many important roles in glucose balance, Dr. Betul Hatipoglu, a professor of medicine at Case Western Reserve University School of Medicine, who was not involved in the study, told The Epoch Times. “Although larger studies to prevent diabetes [with vitamin D] failed to show definite benefit.”
Rather than vitamin D being the cause for the blood sugar improvement, Hatipoglu pointed to the hypothalamus, a brain region that coordinates the nervous system and helps regulate body temperature, hunger, sleep, and emotional responses.
Dysfunction in the hypothalamus has been linked to metabolic problems and may be what daylight exposure affected to produce better blood sugar control.
“It is possible stress hormones and the sympathetic nervous system played a role,” Hatipoglu said.
Beyond vitamin D, ultraviolet rays from sunlight can help release nitric oxide, which may help reduce stress and improve blood vessel function—effects that could benefit metabolic health.
Study Limitations
Although the researchers used a study design that strengthens the reliability of the results, there were several important limitations.
The small number of people involved—13 in total—means that the findings should be interpreted cautiously. Larger studies over longer periods, such as weeks or even months, are needed to see if the effects are lasting and clinically meaningful.
Another limitation is that most participants were older adults, with an average age of 70, and 12 were at least 65. Because of this, researchers can’t be sure if the same effects would be seen in younger people or more diverse populations.
The study authors also noted that while their analysis identified some potential indicators of how natural light might influence health, the results weren’t strong enough to make precise predictions, likely because of the small number of participants.
Despite these limitations, Schrauwen emphasized that even over a short period, daylight had a measurable effect, suggesting that this simple environmental change warrants further study as a complement to diabetes management.