Chronic circadian desynchronization decreases the survival of animals withcardiomyopathic heart disease

Shift work is associated with increased cardiovascular morbidity and mortal ity. Whereas it has been suggested that continuous shifting of the circadia n clock/sleep-wake cycle may have negative effects on health, there is very little experimental evidence to support such a hypothesis. Cardiomyopathic Syrian hamsters were either maintained on a fixed light-dark (LD) cycle (n = 31) or were subjected to a 12-h phase shift in the LD cycle on a weekly basis (n = 32). The duration of the life span was recorded for each animal. Chronic reversal of the external LD cycle at weekly intervals resulted in a significant decrease in the survival time in cardiomyopathic hamsters wit h the median life span being reduced by 11%. Disrupting normal circadian rh ythmicity in an animal susceptible to early mortality due to cardiac diseas e results in a further decrease in longevity. The deleterious effects of th e chronic phase shifts in the LD cycle in cardiomyopathic hamsters may be r elated to reports of increased cardiovascular morbidity and mortality in hu mans engaged in shift work.