Overnight Light Exposure May Contribute to Obesity

Observing that the body’s bioclock regulates energy production and metabolism, and that this bioclock is synchronized by light information, Ohio State University (Ohio, USA) researchers submit that the global increase in the prevalence of obesity and metabolic disorders coincides with the increase of exposure to light at night and shift work.   Laura K. Fonken and colleagues exposed mice exposed to a relatively dim light at night for an eight-week period, and observed that the animals experienced a body mass gain that was about 50% more than other mice that lived in a standard light-dark cycle.  Compared to mice in the standard light-dark cycle, those in dim light at night showed significantly higher increases in body mass, beginning in the first week of the study and continuing throughout. By the end of the experiment, light-at-night mice had gained about 12 grams of body mass, compared to 8 grams for those in the standard light-dark cycle. The dim light-at-night mice also showed higher levels of epididymal fat, and impaired glucose tolerance – a marker of pre-diabetes. Further, although the dim light-at-night mice didn't eat more than others, they did change when they ate: the dim light-at-night mice ate 55% of their food during the daylight hours, compared to only 36% in the mice living in a standard light-dark cycle. Observing that:  “These results suggest that low levels of light at night disrupt the timing of food intake and other metabolic signals, leading to excess weight gain,” the researchers submit that: “These data are relevant to the coincidence between increasing use of light at night and obesity in humans.”