According to June 2019 research – “Association of Exposure to Artificial Light at Night (ALAN) While Sleeping with Risk of Obesity in Women” – published on line in JAMA (Journal of the American Medical Association) Internal Medicine, “artificial light at night while sleeping was significantly associated with increased risk of weight gain and obesity, especially in women who had a light or a television on in the room while sleeping. Associations do not appear to be explained by sleep duration and quality or other factors influenced by poor sleep.”
Researchers from the National Institute of Environmental Health Sciences and the National Institutes of Health used the Sister Study, “a nationwide prospective, cohort study investigating environmental and genetic risk factors for breast cancer, with a total of 50,884 US and Puerto Rican women, who were recruited from July 2003 through March of 2009, as basis for their conclusions on ALAN study.
Prior animal research determined that, “the hypothesis that light exposure at night may have direct effects on melatonin signaling, sleep disruption, and circadian rhythms, which could result in weight gain and obesity,” was verified.
Initial screening asked the type of artificial light at night, if any, that were present at sleep time. Responses included,” “light from a small nightlight or clock radio,” “light from other rooms,” “light from outside shining in through windows at night, such as car headlights, street lights, or porch lights,” “light from a television on in the room for most or all of the night,” “1 or more lights on in the room,” and “daylight.”
Baseline anthropomorphic data – height, weight, hip and waist circumference, and BMI (body mass index) – was obtained for classifications into normal, overweight, or obese status. Based on the exclusion criteria, 43,722 women, who were followed for five years, were included into the final analysis.
The researchers determined that, “in particular, sleeping with a television or a light on in the room was positively associated with gaining 5 kg or more and the development of overweight and obesity, even after adjusting for measures of inadequate sleep, diet, and physical activity.”
It was further noted that, “this observation, although in line with findings from animal studies, appears to be the first epidemiologic evidence of an association between ALAN, while sleeping and risk of weight gain and obesity.”
These results, according to the investigators, mean that artificial light exposure at night should be addressed in obesity prevention discussions.