A new study has shown that people who sleep with the light on or while watching TV or using mobile phones were inclined to put on weight.
In a survey, researchers from Leiden University Medical Centre, Netherlands found that artificial lights disrupted the body clocks and also the brown fat cells that burned calories.
According to the researchers, on an average people stayed online for about 20 hours a week and for 16 to 24-year-olds this figure rises to over 27 hours.
According to researcher Sander Kooijman, the increasing prevalence of obesity was associated with a disrupted sleep-wake pattern in humans and coincided with the availability of artificial light.
Sander Kooijman and colleagues' study is published in the Proceedings of the National Academy of Sciences of the United States of America.
Artificial light exposure had been linked to weight gain for several years.
The researchers at LUMC defined artificial light as any light that was not from the sun, including overhead lighting, computer screens, smart phones and streetlights.
According to an article published in 2013 in the Federation of American Societies for Experimental Biology journal, mice fed with a low-fat diet but exposed to artificial light for prolonged periods of time actually gained more weight than mice on a high-fat diet.
The research team from LUNC looked into a type of fat known as brown adipose tissue (BAT) or brown fat, which plays a key role in energy expenditure by changing energy from food into heat. In other words BAT burned calories.
The mice were exposed to artificial lights for 12, 16, and 24 hours per day for five weeks. The researchers found that though they consumed the same diet, mice exposed to artificial light for 24 hours showed significantly higher fat increases than those exposed to 12 hours of light.
Further studies showed that prolonged artificial light exposure attenuated BAT activity, which increased body fat. It was shown that the longer the exposure to artificial lights, the greater was the reduction of conversion of fatty acids and glucose into heat in mice.
Assuming the extrapolation of data to humans, Patrick C N Rensen said the researchers' observations might implicate that the current obesity epidemic was at least partly due to increased light pollution.