Disrupted light-dark cycle induces obesity with hyperglycemia in genetically intact animals.

BACKGROUND: The environmental light-dark (LD) cycle entrains the circadian clock located in the suprachiasmatic nucleus (SCN) of mammals. Recent studies of genetically impaired animals with clock gene mutations have revealed associations between metabolic disorders and the circadian clock. However, whether such disordered phenotypes are due to a loss of circadian clock function within specific metabolically relevant tissues, or the result of disrupted circadian behavioral activities governed by the SCN remains unknown.

OBJECTIVES: The present study examines the effect of disrupted LD cycles that might perturb the circadian clock in the SCN and peripheral organs on a high-fat/high-sucrose diet-induced obesity in genetically intact mice.

METHODS: The behavioral patterns of the mice were disturbed under an ultradian 3 h light-3 h dark cycle (LD 3:3) due to light-induced direct suppression of the behavior (masking effect).

RESULTS: Obesity with hyperglycemia was significantly enhanced and levels of hemoglobin A1c were significantly higher under LD 3:3 compared with LD 12:12.

CONCLUSIONS: These findings provide a link between metabolic disorders and the "environmental mutation" in genetically intact animals.