The increased risk of type 2 diabetes and obesity seen in people who keep unusual hours may be tied to daily, or circadian, rhythms relating to the blood-glucose-regulating hormone insulin.

Carl Hirschie Johnson and his group at Vanderbilt University in Nashville, Tennessee, showed that mice are less responsive to insulin during the day — when they rest. The researchers disrupted the day–night cycles of mice by exposing them to continuous light or by knocking out a gene that is associated with the circadian clock. When fed a high-fat diet, the disrupted mice became fatter than non-disrupted animals.

The authors suggest that the human internal clock could be targeted to modify metabolic diseases.

Curr. Biol. http://dx.doi.org/10.1016/j.cub.2013.01.048 (2013)