Night, Light and Weight

July 26th, 2019 | Posted in Info

You may have heard about the benefits of sleeping in total darkness in order to get a good night’s sleep. But the benefits go beyond feeling rested on waking.

Sleeping with a television or light on in the room may be a risk factor for gaining weight or developing obesity in women, according to new research. Just switching off the lights at night and sleeping in total darkness could reduce obesity.

The data comes from a questionnaire filled out by over 40 thousand women aged 35-74 years with no history of cancer or cardiovascular disease and who were not shift workers, daytime sleepers or pregnant when the study began. Here’s what they found:

  • Using a small night light was not associated with weight gain.
  • Sleeping with light from a television or ordinary light led to an increased risk of gaining 5kg (11 pounds) over the 5 year follow up period.
  • Light coming in from outside the room had a modest effect on weight gain.

Why Does Light Affect Weight?

Human beings have evolved to experience daylight during the day and darkness at night. Light suppresses the production of the sleep hormone, melatonin, and disrupts the 24 hour light-dark cycle of our circadian rhythm. The alteration in hormones and biological processes at night caused by artificial light may raise the risk of health problems, as well as contributing to weight gain.

Light at night is likely to reduce the quality of sleep and this may contribute to weight gain as not getting sufficient good quality sleep affects blood sugar and insulin.

Other Factors

Although there are likely to be other confounding factors that could explain the association between artificial light at night and weight gain the findings did not change when other factors were taken into account. These factors included age, having a spouse or children in the home, race, socio-economic status, calories consumed and physical activity.

It’s a No-Brainer – Sleep in the Dark

Obviously, eating an unhealthy, overly calorific diet and not doing enough physical activity are major contributors to weight gain but it’s good to know that something as simple as sleeping in the dark could make a positive difference. If necessary use an eye mask to block out light that is out of your control.

Sweet Dreams!

And for even more well being tips see the blogpost: Hug it Better and A Walk in the Park.


1. Yong-Moon, Park M, et al. Association of Exposure to Artificial Light at Night While Sleeping With Risk of Obesity in Women. JAMA Internal Medicine, 2019