Sleeping with artificial light at night associated with weight gain in women

June 10, 2019

Science Daily/NIH/National Institute of Environmental Health Sciences

Sleeping with a television or light on in the room may be a risk factor for gaining weight or developing obesity, according to scientists at the National Institutes of Health. The research, which was published online June 10 in JAMA Internal Medicine, is the first to find an association between any exposure to artificial light at night while sleeping and weight gain in women. The results suggest that cutting off lights at bedtime could reduce women's chances of becoming obese.

The research team used questionnaire data from 43,722 women in the Sister Study, a cohort study that examines risk factors for breast cancer and other diseases. The participants, aged 35-74 years, had no history of cancer or cardiovascular disease and were not shift workers, daytime sleepers, or pregnant when the study began. The study questionnaire asked whether the women slept with no light, a small nightlight, light outside of the room, or a light or television on in the room.

The scientists used weight, height, waist and hip circumference, and body mass index measurements taken at baseline, as well as self-reported information on weight at baseline and follow-up five years later. Using this information, the scientists were able to study obesity and weight gain in women exposed to artificial light at night with women who reported sleeping in dark rooms.

The results varied with the level of artificial light at night exposure. For example, using a small nightlight was not associated with weight gain, whereas women who slept with a light or television on were 17% more likely to have gained 5 kilograms, approximately 11 pounds, or more over the follow-up period. The association with having light coming from outside the room was more modest.

Also, the scientists wondered if not getting enough rest factored into the findings.

"Although poor sleep by itself was associated with obesity and weight gain, it did not explain the associations between exposure to artificial light while sleeping and weight," said corresponding author Dale Sandler, Ph.D., chief of the Epidemiology Branch at the National Institute of Environmental Health Sciences (NIEHS), part of NIH.

Co-author Chandra Jackson, Ph.D., head of the NIEHS Social and Environmental Determinants of Health Equity Group, is interested in racial disparities in sleep health. She notes that for many who live in urban environments, light at night is more common and should be considered. Streetlights, store front neon signs, and other light sources can suppress the sleep hormone melatonin and the natural 24-hour light-dark cycle of circadian rhythms.

"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."

The authors acknowledge that other confounding factors could explain the associations between artificial light at night and weight gain. However, their findings did not change when analyses controlled for characteristics that may be associated with exposure to light at night. These factors included age, having an older spouse or children in the home, race, socioeconomic status, calories consumed, and physical activity. Also, the study did not include men.

Lead author Yong-Moon (Mark) Park, M.D., Ph.D., is a postdoctoral fellow in Sandler's group. He said the research suggests a viable public health strategy to reduce obesity incidence in women.

"Unhealthy high-calorie diet and sedentary behaviors have been the most commonly cited factors to explain the continuing rise in obesity," Park said. "This study highlights the importance of artificial light at night and gives women who sleep with lights or the television on a way to improve their health."

https://www.sciencedaily.com/releases/2019/06/190610130121.htm

Physical inactivity and restless sleep exacerbate genetic risk of obesity

Findings reported at ASHG 2017 Annual Meeting

October 20, 2017

Science Daily/American Society of Human Genetics

Low levels of physical activity and inefficient sleep patterns intensify the effects of genetic risk factors for obesity, according to new results.

Andrew Wood, PhD, postdoctoral researcher, who presented the work; Timothy Frayling, PhD, Professor; and their colleagues at the University of Exeter Medical School study the genetics of body mass index (BMI) and Type 2 Diabetes. In the past, Dr. Frayling explained, it has been difficult to measure interactions between genetic risk factors and aspects of environment and lifestyle in a systematic way.

"Until recently, physical activity and sleep patterns could not be measured with as much precision as genetic variants, and we relied on diaries or self-report, which can be very subjective," Dr. Frayling said. In contrast, the new study made use of wrist accelerometer data, which is more objective and quantifiable, and a large genetic dataset from about 85,000 UK Biobank participants aged 40 to 70.

"We wanted to find out if obesity-related genes and activity level have an interactive effect on obesity risk -- if there is a 'double whammy' effect of being both at genetic risk and physically inactive, beyond the additive effect of these factors," said Dr. Wood. The researchers computed a genetic risk score for each participant based on 76 common variants known to be associated with elevated risk of obesity, and analyzed this score in the context of accelerometer data and participants' BMIs.

They found the strongest evidence to date of a modest gene-activity interaction. For example, for a person of average height with 10 genetic variants associated with obesity, that genetic risk accounted for a 3.6 kilogram increase in weight among those who were less physically active but just 2.8 kilograms among those who were more active. Results were similar in analyses of sleep patterns; among participants with some genetic risk of obesity, those who woke up frequently or slept more restlessly had higher BMIs than those who slept more efficiently.

The researchers are currently examining whether this interaction between genetics and physical activity differs between men and women. They are also studying the effects of patterns of activity -- for example, whether a consistent level of moderate activity has different effects from overall low levels punctuated by periods of vigorous activity.

"We hope these findings will inform clinicians who help people lose or maintain their weight, and contribute to the understanding that obesity is complex and its prevention may look different for different people," said Dr. Frayling. "Ultimately, with further research, we may have the scope to personalize obesity interventions," he said.

https://www.sciencedaily.com/releases/2017/10/171020092240.htm