Why you shouldn’t sleep with the light on

by | Diet and Weightloss, Hormone Health, What We're Talking About

Being exposed to too much artificial light such a television or light on in the bedroom while sleeping ups the risk of weight gain and obesity in women.

Disruption to sleep patterns, such as what can happen during shift work, is now recognised as an important risk factor for weight gain and metabolic abnormalities. Shift work is a challenge to the body’s natural circadian rhythm.

This is compounded by being exposed to light at night, which suppresses the creation of melatonin. Melatonin (see story this issue) plays a key role in regulating hormones such as insulin, cortisol and leptin.

Now scientists are building upon the research in shift workers to see how artificial light can influence sleeping habits and body weight. In the modern world, exposure to light at night is common.

Be it street lights, home lights or the screens from electronic devices, it all adds up to potentially unwanted artificial light exposure when the body should be powering down and up-regulating melatonin production.

Just how much artificial light exposure can affect health has been the subject of new research. This research took a novel direction by looking at light exposure during sleep such as artificial light from lights left on in the bedroom or having a television on in the background.

The research team looked at health and lifestyle data of over 43,000 women – none of whom were shift workers nor slept during the daytime.

Questionnaires asked if the women slept with no light, a night light, light outside the room or had a light or television on in the room. Over many years, body weight and other measures of obesity such as waist circumference were recorded.

Exposure to artificial light at night while sleeping was significantly associated with increased risk of weight gain and obesity. This was especially evident in women who had a light or a television on in the room while sleeping.

Using a small night light was not linked to weight gain. Having a light on outside of the room had less of an association with weight gain.

Women who reported poor sleep patterns were more likely to experience weight gain, but these sleep disruptions did not explain the link between light exposure while sleeping and weight gain.

Nor did the link change when allowance was made for factors such as age, having an older spouse, having children at home, physical activity and a range of other factors. It seemed to be something specifically related to artificial light exposure.


There’s now much public awareness about the need to reduce light and screen exposure at night before bed to aid good sleep habits.

This new research is the first to find that even exposure to artificial light while sleeping can potentially alter sleep patterns and lead to metabolic and hormonal changes that can promote weight gain.