Natural daylight improves the metabolism
Artificial light disrupts the body's internal clock
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metabolic diseases have reached epidemic proportions in society. It is not only a lack of exercise that is responsible for this, but also staying awake for long periods, shift work or artificial light indoors. The body's internal biological clock is then no longer in sync with the natural day-night rhythm. As people spend almost 90 percent of their time indoors, they are only exposed to natural light for a few hours or even minutes a day. To understand how daylight affects human metabolism and in particular blood glucose control, a team from the University of Geneva (UNIGE), Geneva University Hospitals (HUG), Maastricht University and the German diabetes Center (DDZ) in Düsseldorf studied thirteen volunteers with type 2 diabetes in a controlled environment. When exposed to natural light, the participants had more stable blood glucose levels; their general metabolic profile also improved. The results, published in the journal Cell Metabolism, are the first evidence of the positive effect of natural light on people with type 2 diabetes.
As in all living beings, physical processes in humans are also influenced by the day-night rhythm (circadian rhythm). A central "internal clock" in the brain controls and synchronizes the "clocks" in organs such as the liver or skeletal muscles. "We have known for some years that the disruption of the day-night rhythm plays an important role in the development of metabolic disorders, which affect an increasing proportion of the Western population," explains Professor Charna Dibner from the Faculty of Medicine at UNIGE and HUG. She led the study together with Professor Joris Hoeks from Maastricht University and Professor Patrick Schrauwen from the DDZ.
"We spend a large part of our days under artificial lighting, which has a lower light intensity and a narrower wavelength spectrum than natural light. Natural light synchronizes the internal biological clock more effectively with the environment. We wanted to know whether the lack of natural light could be responsible for metabolic diseases such as type 2 diabetes," adds Hoeks.
More stable blood sugar levels with natural light
The research team recruited 13 volunteers with type 2 diabetes who were 65 years or older. They spent four and a half days in specially designed living rooms at Maastricht University, which were illuminated either with natural light through large windows or with artificial light. After a break of at least four weeks, they returned for a second session, this time in the other lighting environment. "This allowed us to examine the same people under both conditions. Individual variations in the results could thus be limited," explains Hoeks. "Apart from the light source, other parameters such as meals, sleep, physical activity or screen time were not changed."
Despite the short duration of the experiment, the team was able to identify significant differences: In the people exposed to natural light, blood glucose levels were within the normal range for a longer period of time per day and showed less fluctuation - "two important factors that indicate that our subjects with diabetes were better able to control their blood glucose levels," explains Patrick Schrauwen. He is a scientist in the Energy Metabolism working group at the DDZ, which is headed by Professor Michael Roden, Scientific Director and Spokesman of the Board of Directors of the DDZ and Director of the Department of Endocrinology and Diabetology at Düsseldorf University Hospital. "In addition, their melatonin levels were slightly higher in the evening and their lipid metabolism was also better," adds Schrauwen.
In order to better understand the positive metabolic changes observed, the scientists took blood and muscle samples from the volunteers before, during and after each light treatment. "We analyzed the regulation of molecular clocks in the cultured skeletal muscle cells together with lipids, metabolic products and gene transcripts in the blood. The results clearly show that the internal clock and metabolism are influenced by natural light. This could be the reason for the better blood sugar regulation and the better coordination between the central clock in the brain and the clocks in the organs," explains Charna Dibner.
The results are to be confirmed under real conditions
This study - the world's first controlled crossover study (one person, several treatment conditions) - only examined a small group of older people with type 2 diabetes over a short period of time. But it is the first evidence of the positive effect of natural daylight on metabolism compared to artificial light, which people are exposed to most of the time. "The next step will be to investigate the interactions between natural light and metabolic health under real-life conditions. Volunteers will be equipped with light detectors and glucose meters over several weeks," says Jan-Frieder Harmsen, lead author of the study, former PhD student in Hoeks' research group and currently a postdoctoral researcher at RWTH Aachen University. "This study also highlights the often overlooked impact of building architecture on our health."
Note: This article has been translated using a computer system without human intervention. LUMITOS offers these automatic translations to present a wider range of current news. Since this article has been translated with automatic translation, it is possible that it contains errors in vocabulary, syntax or grammar. The original article in German can be found here.
Original publication
Jan-Frieder Harmsen, Ivo Habets, Andrew D. Biancolin, Agata Lesniewska, Nicholas E. Phillips, Loic Metz, Juan Sanchez-Avila, Marit Kotte, Merel Timmermans, Dzhansel Hashim, ...Achim Kramer, Patrick Schrauwen, Charna Dibner, Joris Hoeks; "Natural daylight during office hours improves glucose control and whole-body substrate metabolism"; Cell Metabolism, Volume 38
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