Some time back – maybe while I was researching my posts on sleep issues or on heart problems related to distance running – I came across research suggesting that people who slept fewer hours at night – or maybe it was people who slept in the daytime – tended to have more problems with gaining weight. The suggestion at the time, as I recall, was that maybe they were more inclined to snack, late at night.
That could be. But an article in Popular Mechanics (Leman, 2022) cites a study by Mason et al. (PNAS, 2022), investigating the effects of ambient light during one’s sleep. Northwestern University (Paul, 2022) elaborates on that study, explaining that human physiology responds to light at night as it does in daytime:
[L]ight exposure during daytime increases heart rate via activation of the sympathetic nervous system, which kicks your heart into high gear and heightens alertness to meet the challenges of the day. …
Investigators found insulin resistance occurred the morning after people slept in a light room. Insulin resistance is when cells in your muscles, fat and live don’t respond well to insulin and can’t use glucose from your blood for energy. To make up for it, your pancreas makes more insulin. Over time, your blood sugar goes up.
An earlier study published in JAMA Internal Medicine looked at a large population of healthy people who had exposure to light during sleep. They were more overweight and obese ….
The study tested the effect of sleeping with 100 lux (moderate light) compared to 3 lux (dim light) in participants over a single night. …
Tips to reduce light during sleep
Don’t turn lights on. If you need to have a light on (which older adults may want for safety), make it a dim light that is closer to the floor.
Color is important. Amber or a red/orange light is less stimulating for the brain. Don’t use white or blue light and keep it far away from the sleeping person.
Blackout shades or eye masks are good if you can’t control the outdoor light. Move your bed so the outdoor light isn’t shining on your face.
According to Wikipedia (see ScopeCalc), the 3 lux level tested in that study would be similar to the brightness outdoors at the dark limit of civil twilight – that is, when you can just barely see outdoor objects clearly enough to get by without artificial lighting, roughly a half-hour before sunrise or a half-hour after sunset (in a location without light pollution).
The 100 lux level would be comparable to a very dark overcast day, or a little brighter than an office building hallway. Paul (2022) seemed to feel that a TV screen (or, presumably, a computer monitor) would be bright enough to have such effects. Again quoting one of the study authors, “If you’re able to see things really well, it’s probably too light.” Popular Mechanics (Leman, 2022) suggested using a night light rather than a lamp, and arranging things so that no lights are directly visible from the bed.
My thought, upon reading these materials, was that sleeping with too much light – due to either lights in the room or daytime sleeping without blackout curtains – could stimulate weight gain, regardless of snacking, because of the physiological effects of exposure to light. To me, as a person who runs at night during the hot months, and who feels moreover that his metabolism has changed within the past few years, this research did support the common-sense conclusion that I should make sure the bedroom stays dark during sleep hours.
Running & Biking 