Boosting exposure to bright light during the daytime and dimming the lights in the evening could help to improve blood sugar control in people with pre-diabetes, data suggests.
Light plays a key role in synchronising the body’s internal or circadian clock – which controls the timing of multiple biological processes – to the 24-hour day-night cycle.
Previous research has suggested exposure to light at night can disrupt these rhythms, while working night shifts has been associated with a greater risk of obesity, cardiovascular disease and type 2 diabetes. There is also evidence that being exposed to too little light during the daytime may disrupt the rhythms, resulting in poorer sleep.
To investigate how light exposure affects people’s metabolism, Jan-Frieder Harmsen and Prof Patrick Schrauwen, of Maastricht University Medical Centre in the Netherlands, and colleagues brought 14 overweight individuals with pre-diabetes into specially designed respiration chambers – airtight cabins that can measure people’s energy expenditure using various sensors – for two 40-hour sessions.
During one session they were exposed to bright light – roughly equivalent to the lighting in a supermarket freezer aisle – between 8am and 6pm, followed by dim light during the evening and darkness after 11pm. During the other session, the lights were kept dimmed – though bright enough to see – during the daytime, followed by bright light during the evening and darkness after 11pm. Meal content and timing was kept constant between the two sessions.
Pre-diabetes and type 2 diabetes are characterised by high blood sugar levels, which gradually damage blood vessels and vital organs. Exposure to bright daytime lighting was associated with better blood sugar control. Participants also burned more calories after the evening meal and overnight, compared with when daytime lighting was dim. In the long-term, burning slightly more calories after each meal could help prevent weight gain, Schrauwen said.
The scientists also noticed a greater difference in body temperature between day and night when participants were exposed to more naturalistic light patterns. Not only does a drop in body temperature at night help to initiate sleep, it is closely tied to blood pressure control.
“Pre-diabetes is often also associated with higher blood pressure, and so potentially a brighter day and dimmer evening can contribute to better blood pressure regulation,” Harmsen said. The results were published in Diabetologia, the journal of the European Association for the Study of Diabetes.
“Many people live under suboptimal light conditions; often the light in their houses or offices isn’t bright enough, and they are exposed to light at night from their computers, and so on,” said Schrauwen. “We are quite convinced that all these factors contribute to the development of diabetes. It’s not only eating too much or exercising too little, we think that this 24-hour culture is a major factor.”
Based on these results, he said, people should try to boost their daytime light exposure and keep the lights dim during the evening. “We know that a disturbed metabolism is so important in the development of diabetes, so if we have ways to improve that, we should do them,” he said.
Frank Scheer, a professor of medicine at Harvard Medical School’s sleep medicine division, said: “This research highlights the influence of our daily light exposure on our bodily functions; not only in the regulation of melatonin – a hormone typically released at night, and which is associated with sleepiness – which has been known for decades, but also for metabolism.
“Melatonin was recently discovered to play an important role in glucose regulation and other aspects of metabolism, so future studies are needed to test to what degree the effects of light are dependent on its suppression, and if some individuals are genetically more susceptible.”