Exposure to Natural Light Improves Metabolic Health

By Health Correspondent

An international research team has found the first direct evidence that natural daylight can benefit people with type 2 diabetes more than artificial light.

Metabolic diseases such as type 2 diabetes are increasing, partly due to modern lifestyles that disrupt the body’s natural circadian rhythm. People now spend nearly 90% of their time indoors, limiting their exposure to natural daylight.

To study the effect of light on metabolism, researchers from the University of Geneva (UNIGE), the University Hospitals of Geneva (HUG), Maastricht University, and the German Diabetes Center (DDZ) carried out a controlled study with 13 volunteers aged 65 and over who have type 2 diabetes. The results were published in Cell Metabolism.

"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," notes Charna Dibner, associate professor at the UNIGE Faculty of Medicine and at HUG.

Researchers believe artificial lighting may contribute to this problem.

"We largely spend our days under artificial lighting, which has a lower light intensity and a narrower wavelength spectrum than natural light. Natural light is also more effective in synchronizing the biological clock with the environment. Could the lack of natural light be to blame for metabolic diseases such as type 2 diabetes?" adds Joris Hoeks.

How the study worked

Each volunteer spent 4.5 days in specially designed rooms at Maastricht University, once under natural daylight and once under artificial light, with at least four weeks between sessions.

"This experimental model allows us to examine the same people under both conditions, which limits the individual variability in our results," explains Joris Hoeks. "Apart from the light source, all the other lifestyle parameters - meals, sleep, physical activity, screen time, etc. - were kept strictly identical."

Clear health benefits

Even over a short period, exposure to natural light led to better blood sugar control. Participants spent more time each day with glucose levels in the normal range and showed less variation.

"Two important elements that indicate that our volunteers with diabetes managed to control their sugar levels better," says Patrick Schrauwen from DDZ. "In addition, their melatonin level was a little higher in the evening, and fat oxidative metabolism was also improved."

Further testing showed that natural light influenced the body’s internal clocks and metabolism, helping improve coordination between the brain and other organs.

Next steps

Although the study was small and short-term, it is the first controlled trial to show the metabolic benefits of natural daylight compared with artificial light.

"The next step will be to study the interactions between exposure to natural light and metabolic health in real-life conditions, by equipping volunteers with light detectors and glucose measurement tools for several weeks," say Jan-Frieder Harmsen. "This study also highlights the often-overlooked impact of building architecture on our health.”

The study was supported by the VELUX Stiftung and Daylight Academy, the Swiss National Science Foundation, and the Vontobel Foundation.