Falling asleep to a playlist of recommended Youtube videos or reality TV may be the digital age’s lullaby, but it can also carry unintended consequences: The sustained glow of light has striking connections to weight gain, according to analysis published Monday in JAMA Internal Medicine.
When it comes to light exposure, blue light (the kind that comes from screens) takes the most heat, but a new study speaks to issues that arise from a lighted bedroom in general, drawing on evidence from surveys of 43,711 women collected between 2003 and 2009. When these authors followed up in 2015, they found that women who were exposed to artificial light while they slept were more likely to gain weight.
Specifically, women who slept with light or television on in the bedroom were 17 percent more likely to have gained at least five kilograms (around 11 pounds) or more over that period of time.
Dale Sandler, Ph.D., a senior investigator at the National Institutes of Health, and lead study author, says people don’t need to throw away their nightlights just yet: The research shows that small amounts of light don’t have nearly the same effect as the constant glow of a TV, or the glare of a lamp left on overnight.
“We did see that associations got stronger with increasing amounts of light, if we classified light from none, to small nightlight, to light from outside the room, to having the TV on or a light on in the room,” Sandler tells Inverse. “In fact, there were no associations between having a nightlight on and weight gain.”
The Relationship Between Artificial Light and Weight Gain
Sandler’s study divided light exposure into four categories:
- Some 7,807 lucky women slept in complete darkness.
- The biggest group slept with a small nightlight.
- Others slept with a light from outside the bedroom.
- The fourth group slept with a light or TV in the room.
The women in that last group, who slept with the TV or lights on, had the highest likelihood of gaining extra weight by far. Those who slept with lights on in another room had a far more modest effect, and only a 3 percent likelihood of that extra five kilograms of weight gain.
Artificial light sources still had a powerful effect. Any amount of artificial light at night was associated with higher likelihood of obesity at baseline (before the study period started), and overall, 19 percent of women who were exposed artificial light while sleeping crossed into obese territory (going by BMI) over the course of the study.
Why Artificial Light in the Bedroom Might Result in Weight Gain
The study presents a good reason to look more closely at the connection between artificial light exposure in the bedroom and weight, which the study’s authors suggest probably has to do with circadian rhythm.
Light exposure at night can throw off hormone release cycles associated with light and darkness, added Chandra Jackson, Ph.D., a study co-author and head of the National Institute of Environmental Health Sciences Social and Environmental Determinants of Health Equity Group.
“Humans are genetically adapted to a natural environment consisting of sunlight during the day and darkness at night,” Jackson said. “Exposure to artificial light at night may alter hormones and other biological processes in ways that raise the risk of health conditions like obesity.”
TV Light vs. Lamp Light
Although the research groups and TV light and regular, yellow light, there’s some evidence that it might be worth treating each separately. As the authors note in the paper, blue light from screens, particularly computers or phones, could lead to greater effects on circadian rhythm, compared to other light sources.
In their paper, the scientists divide light in the bedroom specifically and light from a TV, and noted that “associations with television and light were similar.”
Sandler says that the study doesn’t take wavelength into account specifically, so it’s still possible that light source may matter:
“There is some evidence that the type of light could make a difference,” Sandler says. “This is something that will need to be addressed in other studies.”
Until we know for sure, this paper is evidence that the best policy is turn off the lights and the TV. Whether that’s for health, or other purposes, going after a few hours of darkness at night might be worth it.
Design, Setting, and Participants: Artificial light at night while sleeping reported at enrollment, categorized as no light, small nightlight in the room, light outside the room, and light or television in the room.
Exposures: Prevalent obesity at baseline was based on measured general obesity (body mass index [BMI] ≥30.0) and central obesity (waist circumference [WC] ≥88 cm, waist-to-hip ratio [WHR] ≥0.85, or waist-to-height ratio [WHtR]≥0.5). To evaluate incident overweight and obesity, self-reported BMI at enrollment was compared with self-reported BMI at follow-up (mean [SD] follow-up, 5.7 [1.0] years). Generalized log-linear models with robust error variance were used to estimate multivariable-adjusted prevalence ratios (PRs) and relative risks (RRs) with 95% CIs for prevalent and incident obesity.
Main Outcomes and Measures: Among the population of 43 722 women (mean [SD] age, 55.4 [8.9] years), having any ALAN exposure while sleeping was positively associated with a higher prevalence of obesity at baseline, as measured using BMI (PR, 1.03; 95% CI, 1.02-1.03), WC (PR, 1.12; 95% CI, 1.09-1.16), WHR (PR, 1.04; 95% CI, 1.00-1.08), and WHtR (PR, 1.07; 95% CI, 1.04-1.09), after adjusting for confounding factors, with P < .001 for trend for each measure. Having any ALAN exposure while sleeping was also associated with incident obesity (RR, 1.19; 95% CI, 1.06-1.34). Compared with no ALAN, sleeping with a television or a light on in the room was associated with gaining 5 kg or more (RR, 1.17; 95% CI, 1.08-1.27; P < .001 for trend), a BMI increase of 10% or more (RR, 1.13; 95% CI, 1.02-1.26; P = .04 for trend), incident overweight (RR, 1.22; 95% CI,1.06-1.40; P = .03 for trend), and incident obesity (RR, 1.33; 95% CI, 1.13-1.57; P < .001 for trend). Results were supported by sensitivity analyses and additional multivariable analyses including potential mediators such as sleep duration and quality, diet, and physical activity.
Results: These results suggest that exposure to ALAN while sleeping may be a risk factor for weight gain and development of overweight or obesity. Further prospective and interventional studies could help elucidate this association and clarify whether lowering exposure to ALAN while sleeping can promote obesity prevention.