Editors' ChoiceObesity and Night Work

Why Rats Don't Take Day Jobs

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Science Translational Medicine  17 Feb 2010:
Vol. 2, Issue 19, pp. ec25
DOI: 10.1126/scitranslmed.3000958

Night-shift workers have to be concerned about more than a disruption of their biological clocks: A detrimental desynchrony develops between their brains, which control sleep and the 24-hour biological clock, and their physiology, which is influenced by exercise, feeding, and other environmental cues. Moreover, working at night and sleeping during the day have been associated with hypertension, obesity, and the metabolic syndrome, through unclear mechanisms.

Salgado-Delgado et al. sought to identify the mechanism of these metabolic derangements by examining rats that “worked the night shift,” in which their physiologic cycles are dissociated from their biological clocks. Control rats “worked” during usual active hours for a rat, and “night-work” rats worked during typical rat sleeping hours. Night-work rats worked for 8 hours each day, Monday through Friday for 5 weeks, and could eat and drink freely during this time. The control rats had free access to food, food only in the day, or food only at night. Among the night-shift rats who ate in their normal resting phase (during which they were being forced to work), the investigators observed a significant increase in body weight and retroperitoneal fat mass and loss of the daily rhythm for glucose. The effects were found to result from the feeding schedule, not the work schedule. The deleterious metabolic changes were prevented, however, when feeding was restricted to the normal active phase in the night-shift rats.

This work highlights how examination of a rodent model of a human condition can provide insight into human pathology. Although humans are not rats, these findings are consistent with human studies showing that eating during the normal resting period (the night shift) in the presence of metabolic desynchrony can negatively alter blood glucose and increase abdominal obesity, predisposing to metabolic syndrome, type 2 diabetes, and subsequent cardiovascular disease. Perhaps it would be best not to eat during the night shift.

R. Salgado-Delgado et al., Food intake during the normal activity phase prevents obesity and circadian desynchrony in a rat model of night work. Endocrinology 15 January 2010 (doi:10.1210/en.2009-0864). [Abstract]

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