Night light may be linked to weight gain

Scimex: A Dutch study of mice found exposure to artificial light after dark may be linked to weight gain because the body reacts by burning less energy to keep warm, rather than eating more or curbing activity levels. Brown fat - the 'healthy' fat our bodies burn to stay warm - is inactivated by artificial light during the night, they say, so finding ways to reactivate it may help prevent weight gain associated with unnatural light regimes.

A study in mice suggests that brown adipose tissue may mediate the link between environmental light pollution and a number of obesity-related illnesses, including type 2 diabetes and cardiovascular disease. Recent studies suggest constant light exposure disrupts the sleep-wake cycle, thereby decreasing energy expenditure and promoting weight gain. Sander Kooijman and colleagues explored the effects of day length on the activity of brown adipose tissue (BAT) in mice, noting that BAT plays a central role in energy expenditure by combusting energy from food into heat. The authors exposed mice to artificial light for 12, 16, or 24 hours per day for 5 weeks, following which the authors assessed body weight and composition. Mice exposed to artificial light for 24 hours, compared with 12 hours, had significantly higher fat composition even as their daily food intake remained at baseline. The authors propose that prolonging daily light exposure promotes obesity by decreasing energy expenditure, rather than increasing food intake or modulating physical activity. Further investigation revealed that increased light exposure decreases noradrenergic activation of BAT and thereby reduces conversion of fatty acids and glucose into heat. According to the authors, the study suggests that restoring impaired BAT activity may help overcome the negative consequences of increased light exposure.