Health & Fitness

How light increases women's obesity risk

artificial light
Exposure to artificial light at night may alter hormones and other biological processes. PHOTO | FOTOSEARCH 

Weight gain is an issue that affects many women in Kenya. As such, they are always seeking solutions or remedies to tackle the challenge.

Government statistics from the Kenya Stepwise Survey for Non-Communicable Disease (NCD) risk factors show that overall, 27 percent of Kenyans are either overweight or obese. But the percentage is slightly higher in women (38 percent) than men (17 percent).

Aside from making them vulnerable to ailments such as cancer and cardiovascular diseases, the weight may also pose a threat to women of reproductive age during pregnancy.

Health experts recommend healthy diets and physical exercises for sustainable weight reduction or management. In addition to the above strategies, a new study published in the JAMA Internal Medicine Journal – a publication of the American Medical Association - shows that a seemingly easy task such as switching the lights off at bedtime can keep away obesity.

According to scientists from the US-based National Institutes of Health who conducted the study, sleeping with a television or light on in the room may be a risk factor for gaining weight or developing obesity.


The research is the first to find an association between any exposure to artificial light at night while sleeping and weight gain in women.

During the study, the research team used questionnaire data from 43,722 women.

The participants, aged 35-74 years, had no history of cancer or cardiovascular diseases and were not shift workers, daytime sleepers, or pregnant when the study began.

They were asked whether they slept with no light, a small night-light, light outside their room, or with a light or television on inside the room. To determine the weight of study participants, the researchers relied on self-reported figures, body mass index (BMI), as well as height, waist and hip circumference measurements.

Using this information, the scientists were able to compare obesity and weight gain trends among women exposed to artificial light at night, with those who reported sleeping in dark rooms.

The results varied with the level of artificial light at night exposure.

For example, using a small nightlight (lamp or candle) that provides dim light was not associated with weight gain.

However, women who slept with light or television on were 17 percent more likely to have gained five kilogrammes or more over the follow-up period.

The association with having light coming from outside the room was more modest.

Researchers noted that the findings remained constant irrespective of the participants’ age, race, socioeconomic status, calories consumed, physical activity and family (having an older spouse or children in the home). These factors have been known to influence obesity risk.

Chandra Jackson, a co-author of the study from the National Institute of Environmental Health Sciences (NIEHS) noted that for many people who live in urban environments, light at night is more common and should be considered.

Past studies have indicated that streetlights, store front neon signs and other artificial light sources - both inside and outside the house - can suppress the brain’s production of a sleep hormone known as melatonin which happens at night.

The hormone regulates people’s ‘sleep-wake’ cycle. It also lowers body temperature, blood pressure and glucose levels.

A decline in melatonin therefore impedes sleep quality as well as the body’s ability to regulate glucose levels which leads to weight gain and obesity.

"Humans are genetically adapted to a natural environment consisting of sunlight during the day and darkness at night. Therefore, exposure to artificial light at night may alter hormones and other biological processes in ways that raise the risk of health conditions like obesity," Jackson said.

Yong-Moon (Mark) Park, the lead author of the study, stated that the research findings point to a viable public health strategy to reduce obesity incidence in women.

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

By choosing to sleep with lights off, the brain gets a clear signal to produce sufficient amounts of melatonin, which has many health benefits.

Aside from regulating glucose levels to prevent weight gain, the melatonin hormone also lowers the body’s cholesterol and increases antioxidants that boost the immune system and ward off lifestyle diseases like cancer and hypertension.

It also enhances the proper functioning of the thyroid, pancreas, ovaries, testes and adrenal glands.