Researchers found that exposure to natural sunlight was associated with blood glucose levels remaining within the normal range for a longer period compared with exposure to artificial light.
The findings suggest that something as simple as spending time near a window or in daylight could support metabolic health by helping to regulate the body’s internal clock.
Type 2 diabetes is the most common form of diabetes and is a lifelong condition that occurs when the pancreas does not produce enough insulin or when the body is unable to effectively use the insulin it produces.
Insulin is the hormone responsible for regulating blood glucose levels, and poor blood sugar control over time can increase the risk of serious complications.
Blood Sugar Stayed Normal for Longer
For the study, researchers placed participants in a room with a large window for 4.5 days. The volunteers were exposed to natural daylight for nine hours each day, from 8am to 5pm, without the use of artificial lighting.
The participants’ daily routines were kept as consistent as possible. Their sleep schedules, physical activity, diet and diabetes medication were maintained throughout the experiment.
About one month later, the participants underwent another 4.5-day period under similar conditions, but this time they stayed in a windowless room illuminated only by artificial light.
The researchers found that blood glucose levels remained within the normal range for about 50 per cent of the time when participants were exposed to natural daylight.
Under artificial lighting, however, blood sugar levels remained within the healthy range for approximately 43 per cent of the time.
Although the difference may appear modest, Professor Joris Hoeks, who led the study, said spending prolonged periods with blood glucose outside the normal range could increase the risk of long-term complications, including cardiovascular disease.
How Daylight May Affect Metabolism
The researchers linked the findings to specialised light-sensitive cells in the eyes that help regulate the body's circadian and metabolic rhythms.
These cells respond particularly strongly to short wavelengths of light, including the blue portion of the spectrum, which is abundant in natural daylight.
According to the researchers, exposure to daylight can help reinforce the body’s circadian clock — the internal biological system that regulates sleep, wakefulness and a range of metabolic processes.
A well-regulated circadian rhythm can promote melatonin production at night, improve insulin sensitivity and support the body's ability to metabolise fat and use energy efficiently.
The researchers also noted that a properly functioning body clock could contribute to better sleep, which itself plays an important role in metabolic health.
Experts Call for More Research
Professor Glen Jeffrey of the Department of Visual Neuroscience at University College London, who was not involved in the study, highlighted the broader importance of daylight exposure for human health.
However, he cautioned that larger and more extensive clinical trials would be necessary to confirm the findings and determine how daylight exposure could eventually be incorporated into diabetes management.
The study does not suggest that people with diabetes should abandon established treatments.
Experts stressed that spending time in natural daylight should be viewed only as a possible lifestyle support alongside prescribed medication, healthy eating, physical activity and regular monitoring of blood glucose.
For people living with type 2 diabetes, the findings nevertheless point to a potentially simple addition to daily routines: spending more time in natural daylight, whether outdoors or in a well-lit room with access to sunlight, may have metabolic benefits worth further investigation.