While the study doesn't prove that sleeping with a light on causes weight gain, it suggests the two may be linked, the researchers said.
The results showed that the women who slept with an artificial light or television in the same room were 17 per cent more likely to gain 5kg or more in the five year period. That being said, a direct link between artificial light in a bedroom and overall weight gain is still a bit startling to see. Using this information, the scientists were able to study obesity and weight gain in women exposed to artificial light at night with women who reported sleeping in dark rooms. For example - the women who slept with the light or TV on were 22 percent more likely to put on weight - this could be because a lack of sleep makes you more hungry thanks to hormones that are released when you're exhausted.
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.
The findings are not conclusive however.
"Exposure to artificial light at night may alter hormones and other biological processes in ways that raise the risk of health conditions like obesity". "Further prospective and interventional studies could help elucidate this association and clarify whether lowering exposure to ALAN while sleeping can promote obesity prevention". A study followed nearly 44,000 women for five years and those who left lights on at night gained up to 11lbs (5kg). Health officials recommend taking TVs and other tech devices out of your bedroom in order to support a healthy sleeping environment.
The researchers analysed health and lifestyle data on almost 44,000 U.S. women enrolled in an ongoing study seeking clues to causes of breast cancer.
Among women who weren't obese at the study's, those who reported exposure to any light at night were about 20% more likely to become obese during the study, compared with those who didn't report exposure to light at night.
The findings held even after the researchers took into account factors such as where participants lived (in an urban, suburban or rural area), their household income, their level of caffeine and alcohol consumption, and any experiences of depression or high stress.
This sleep study comes on the heels of another study that found irregular sleep patterns, including not going to bed and waking up at the same time each day or getting different amounts of sleep each night, can put people at a higher risk for obesity, heart disease, hypertension, high blood sugar and other metabolic disorders.