Do you like to fall asleep to the TV? With the lights on? Apparently you’re not alone, lots of other people do too. Dozing off to late-night TV or sleeping with other lights on may mix up your metabolism and lead to weight gain and even obesity, newly reported U.S. research suggests. The National Institute of Health study published this month isn’t proof, but it bolsters evidence suggesting that too much exposure to light at night could pose health risks, including obesity.
Researchers followed 43,722 generally healthy women, ages 35 to 74. About 17,000 slept with a nightlight in the room, while more than 13,000 left a light on outside the bedroom and about 5,000 slept with a television or light on in the bedroom. At the start of the study, women were typically overweight but not yet obese, according to their body mass index (BMI), a ratio of weight relative to height. None of them worked shifts that could interrupt sleep cycles. Controlling for factors such as age, race, physical activity, diet, snacking habits, smoking, alcohol, duration of sleep and other variables, they found that sleeping with the lights on was independently associated with gaining 11 pounds or more over 5 years compared with those who slept in darkness. That amounts to an increase of 10 percent or more in BMI. After almost six years of follow-up, women who slept with a television or light on in the room were 22 percent more likely to be overweight and 33 percent more likely to be obese than women who slept in total darkness. Total darkness meaning there wasn’t even a nightlight or the glow from an alarm clock, window or hallway.
Animal research and smaller studies in humans have also linked prolonged light exposure with weight gain. Another larger study published in the American Journal of Epidemiology involved over 113,000 women. They were part of the Breakthrough Generations Study to find a link between obesity and light exposure at night. The study attempted to determine the root causes of breast cancer; obesity is known to increase risks for breast cancer (discussed in a future post). The study also confirmed that those who slept with any type of light on gained significant weight over their dark roomed counterparts.
The obesity-causing effects of light at night appear to have something to do with the body’s natural clock. The artificial light can delay the production of the sleep hormone melatonin and mess up the body’s circadian rhythm, which can affect mood and the way a person processes food. We already know there’s an association between the number of hours slept and the tendency to eat more calorie-packed foods.
The concern is that artificial light may be disrupting sleep in ways we may not even notice, such that sleep may not be as deep or as sustained. This in turn could affect metabolism or even hunger. Being in a more awake state for longer periods of the day could signal to your body that more food is needed to provide energy for whatever it is that you are doing that’s keeping you awake longer. Less restful sleep could also be increasing stress hormones that in turn could alter metabolism and lead to weight gain. Poorer quality sleep could affect mental health as well, which as a result, could affect eating.
“Evolutionarily we are supposed to be sleeping at night, in a dark place,” said one of the lead authors Dale Sandler, a scientist with the National Institute of Environmental Health Sciences, a division of the National Institutes of Health. “It’s much more important than people realize for a whole variety of health reasons. “Daily exposure to light and darkness helps maintain our 24-hour body clock, which regulates metabolism, sleep-promoting hormones, blood pressure and other bodily functions. Mounting research suggests disrupting that typical sleep-wake cycle may contribute to poor health, increasing risks for high blood pressure, diabetes, depression and now obesity. For this reason she felt confident gender wasn’t a factor and similar results would likely be found in men.
Years ago, I traveled with a friend to a medical conference. We had stayed at Inn Suites so we could each have our own space. When I got up in the middle of the night I noticed the TV was still on in her area. I thought she had fallen asleep while watching and it would end up intruding on her sleep so I quietly turned the TV off only to have her jump awake! She’d been doing this since college and could no longer sleep in silence. She had struggled with her weight for decades, averaging 250 pounds. Clearly other issues impacted her size, but it’s sad to think something as easy as just turning off the TV could have helped.
Sleeping with electronic devices, lights, TV, etc., may be a hard habit to break. Some of us may have family members or room mates who are up later with the lights on. Those who live in crowded housing or in cities may have a harder time controlling the amount of light that comes in from outside the room.
But clearly, research shows properly timed light should be considered an essential part of a healthy life style, along with exercise and good nutrition. We all know getting a good night’s sleep is vital to our health but who knew something as simple as turning off the lights or just adding an eye mask before going to sleep could also reduce weight gain.