This Nighttime Habit May Be Linked To Weight Gain, Study Finds

Leslie Hanson
June 11, 2019

The researchers considered several other compounding factors, like sleep deprivation, which could have played a role in the association between artificial light exposure at night and weight gain.

The questionnaire included questions about exposure to light during sleep, and participants indicated whether they slept with no light, a small night light, light outside of the room, or a light or television on in the room.

"These results suggest that exposure to [artificial light at night] while sleeping may be a risk factor for weight gain and development of overweight or obesity", the researchers conclude.

The researchers analyzed health and lifestyle data on almost 44,000 US women enrolled in an ongoing study seeking clues to causes of breast cancer.

However, most of this research was conducted in night-shift workers who are exposed to high levels of light at night; these results may not apply to the general population.

Ashton suggests that women create a prime sleeping environment for themselves by using tools like eye masks and blackout shades or drapes.


"Exposure to artificial light at night may alter hormones and other biological processes in ways that raise the risk of health conditions like obesity". "It is a medical necessity on par with our food and our fitness".

To get a better idea of how artificial light exposure at night affects women's weight, researchers logged participants' weight, height, waist and hip circumference, and body mass index measurements at the beginning of the study, and compared it to the same data gathered five years later.

At their first check-in, the women were asked to report on their light exposure while they slept - whether they kept lights on in their rooms or in other rooms, whether light shone in through the windows, whether they slept with a TV on, and even from low-light sources such as clock radios. Those who reported sleeping at night in a room with a television on or a light were more likely to gain at least 11 pounds over about five years than those who slept in darkness.

"These new findings won't change the advice to maintain good sleep hygiene, and avoid light and electronic distractions in the bedroom, but they add further strength to the case for this advice". Light coming in from the outside didn't appear to have significant effects on weight, while bedroom light did.

The study, which didn't include men, admits that there are other factors that could explain the weight gain, such as age, race, socioeconomic status, physical activity and calories consumed. He said the research suggests a viable public health strategy to reduce obesity incidence in women.

"It's really important that you have that daytime-nighttime cycle, so that you appropriately regulate hormones, hormones that regulate your sleep, hormones that regulate your hunger, said lead author Dale Sandler, a scientist with the National Institute of Environmental Health Sciences, a division of NIH".

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