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Getting Too Much of This at Night Could Be Affecting Your Metabolism, Study Shows


By now, research has made it clear how important sleep is for good health and longevity. Following a normal sleep-and-wake cycle translates into better brain performance and a lower risk of certain diseases. But did you know that your light-and-dark cycle can have a serious impact on your health as well? A new study shows that following a natural light-and-dark cycle (bright light during the day and no light at night) may improve your body’s metabolism, while too much artificial light could harm it. That’s especially true if you are overweight and insulin resistant.

The Connection Between Metabolism, Natural Light, and Artificial Light 

Published in Diabetologia, the study was conducted by researchers at the NUTRIM School for Nutrition and Translational Research in Metabolism, Maastricht University Medical Center, Maastricht, The Netherlands. The authors predicted that too much artificial light (whether from electronics or indoor lighting) during the evening could disrupt the body’s natural metabolism.

Your metabolism — or, the process by which your body turns nutrients into energy — doesn’t stay the same throughout the day. (That’s why walking at different times of day burns a different amount of calories.) A 2018 study from Current Biology found that people burn the least number of calories at about midnight. Adults also use more energy in the afternoon and early evening.

To test their theory, the researchers recruited 14 volunteers between 40 and 75 years of age, all of whom were overweight and insulin resistant. All the participants underwent two 40-hour experiments. One of the 40-hour experiments exposed the volunteers to bright, artificial light during the day and dim light in the evening. (This was called the bright day, dim evening test.) In the other 40-hour session, volunteers were exposed to dim artificial light during the day and bright light in the evening. (This was called the dim day, bright evening test.) The researchers measured the participants’ metabolism throughout both sessions with blood samples, temperature checks, and other tests. 

The Results of the Study

Ultimately, the authors found that the bright day, dim evening session helped to better regulate metabolism. The volunteers did have higher levels of fat in their blood after breakfast during this natural light cycle. This suggests that the natural light didn’t improve their body’s ability to regulate blood fat levels in the morning. However, the volunteers had lower levels of sugar in their blood before dinner. In effect, the shift from light to dark may have helped signal their bodies to process all the sugar they had eaten. In response to bright day, dim evening, the volunteers also had a higher metabolic rate after dinner, and a healthy metabolic rate during sleep — all of which suggests that their metabolism was functioning well.

In contrast, the dim day, bright evening session didn’t have the same positive outcomes. For instance, it caused the volunteers’ metabolic rate to drop as they slept. This suggests that their bodies were somewhat more “confused” in response to the reversal of natural light, and body processes weren’t functioning optimally at night. Bright light at night also suppressed melatonin levels, which may have made it more difficult for those volunteers to fall asleep.

Of course, the study had its limitations. With just 14 volunteers, the authors can’t be sure that the results apply to everyone. More research is necessary to prove that bright light during the day and dim light at night improves metabolism in overweight people.  

Still, it’s good to know that following a natural light-and-dark cycle (even with artificial light that mimics the natural cycle) can help your body better regulate itself. Be mindful of how much artificial light is in your home at night — and if you need inspiration for how to reduce your screen time throughout the day, check out these helpful tips.  

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