Sleeping with the lights on or a television set on for just one night raises blood sugar, heart rate and insulin resistance, all risk factors for diabetes (PNAS, March 14, 2022;119(12):e2113290119). Five to ten percent of the light can actually get through a closed eyelid.

Your heart rate is supposed to go down when you sleep at night. When it regularly doesn’t go down, you are at increased risk for heart disease and death (Int Heart J, Mar 28, 2020;61(2):289-294). An elevated nightly blood sugar, called the “dawn phenomenon,” increases risk for heart disease and diabetes (PLoS Biology, July 24, 2018). Not getting enough sleep each night also raises nightly sleeping blood sugar (Nutr Diabetes, 2017 May 8;7(5):e266) and sleeping heart rate (J Am Coll Cardiol, Sept 10, 2019;74(10):1304-1314). Not getting at least six hours of sleep each night is associated with weight gain and obesity, inflammation, cardiovascular disease, diabetes, and increased death rate (Curr Cardiol Rev, Feb 2010;6(1):54-61; Curr Opin Cardiol, 2016 Sep; 31(5): 551-565).

Other studies show that sleeping with the lights on increases risk for decreased glucose tolerance and decreased insulin sensitivity (Endocr Rev, 2014;35:648-670; Swiss Med Wkly, 2020;150:w20273). The greater the exposure to light during sleep, the more likely a person is to become diabetic (Sleep Med, 2020;65:1-3).

Why High Blood Sugar During Sleep Increases Risk for Diabetes and Heart Disease
High blood sugar during the day or night increases diabetes risk. When your blood sugar rises, your pancreas releases insulin which lowers blood sugar by driving sugar from the bloodstream into your liver. Your liver quickly fill up with a small amount of sugar and then all the extra sugar is converted to a type of fat called triglycerides. Then your good HDL cholesterol lowers high blood triglyceride levels by carrying the fatty triglyceride molecules into your liver. As your liver starts to fill up with fat, it loses its ability to respond to insulin and accept sugar from the bloodstream and eventually you become insulin resistant and diabetic.

The “dawn phenomenon” is an early-morning increase in blood sugar that can occur naturally between 2 a.m. and 8 a.m. As your body prepares to wake up from deep sleep, it releases increased amounts of growth hormone, cortisol, glucagon and epinephrine which cause your blood sugar to rise and provide extra energy to help you wake up. Both bright lights and not getting enough sleep at night increase levels of these hormones to raise blood sugar.

My Recommndations
Sleeping with the lights on and not getting enough sleep are risk factors for diabetes. If you find it difficult to sleep at night, make sure you close your blinds and curtains, and turn off all the lights, your computer and your television set. Other risk factors for diabetes include:
• having a fasting blood sugar greater than 100 mg/dL blood sugar, or a one-hour-after-eating-a-meal blood sugar greater than 145 mg/dL
• having a prominent belly and small buttocks
• being able to pinch more than two inches of fat under the skin next to your belly button
• having a fatty liver (shown in a sonogram)
• having triglycerides greater than 150 mg/dL
• having HDL cholesterol less than 40
See Belly Fat Predicts Fatty Liver and Diabetes