More Light Exposure During the Day and Less in the Evening Could Help Your Blood Sugar

In the modern world, where technology is always at our fingertips, it is all too common for people to turn on more lights as the sun sets and spend the evenings buried in television, tablet, and phone screens.

A new study, published in Diabetologia, aimed to see whether screen time and the use of electric lights when it’s dark outside had an impact on users’ blood sugar control.

“Our objective was to compare metabolic responses to lighting conditions that resemble the natural light/dark cycle in contrast to suboptimal lighting in individuals at risk of developing metabolic diseases,” the authors said.

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The researchers exposed a group of overweight, insulin-resistant volunteers to bright electric lights from 8 a.m. to 6 p.m. Then they were subjected to dim lights from 6 p.m. to 11 p.m. and darkness for the rest of the night. The total length of their stay in the laboratory was 40 hours.

A second group of volunteers was given the opposite treatment; they were exposed to dim light from 8 a.m. to 6 p.m., followed by brighter lights in the evening.

Researchers made sure to keep all subjects’ meal times and foods consistent. They took blood samples, indirect calorimetry readings, and body temperature readings to determine how well each group responded to the lights.

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The team found that those subjects who were exposed to bright light during the day had higher postprandial triacylglycerol levels after breakfast but lower blood glucose levels prior to dinnertime than those who were exposed to dim lighting. They also had lower blood sugar levels after dinner, when they were exposed to the dimmer light, than those who were exposed to brighter lights in the evening. They burned more calories after their evening meal and overnight.

Melatonin secretion and sleeping metabolic rate were also improved in the group that spent the day in bright light and the evening in dim light. Fasting and postprandial plasma insulin levels and the respiratory exchange ratio were the same between the two groups.

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“Many people live under suboptimal light conditions,” says Patrick Schrauwen, of Maastricht University Medical Centre in the Netherlands. “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. It’s not only eating too much or exercising too little, we think that this 24-hour culture is a major factor.”

As diabetes and other health conditions continue to be major epidemics, research like this may encourage both changes in individual lifestyle habits and larger-scale societal changes such as shifts toward dimmer nighttime lighting in public spaces, dimmer switches in new homes, and architectural choices that let in more natural light.

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