Relationship of body temperature stability to mortality in aging mice.

An age-related decline in the capacity for thermoregulation among homeothermic animals has been observed frequently under conditions of extreme ambient temperatures. We investigated the temporal stability of the internal body temperature of 69 C57BL/6J mice from 25 months of age until death in a controlled, neutral thermal environment. Estimates of temporal variability were calculated over consecutive 1-month intervals using (colonic) body temperature data collected weekly. The results of this longitudinal analysis indicated that the regulation of body temperature, as measured by its temporal stability, became increasingly less precise with advancing age. Body temperature exhibited a significant decline as the animal approached death. Individual differences in body temperature and the temporal regulation of body temperature were significantly correlated with lifespan, although the direction of the relations were opposite. Body temperature correlated positively with lifespan, whereas the temporal stability of body temperature correlated negatively with lifespan. Thus, animals exhibiting higher body temperatures and greater temporal stability also tended to live longer than their cohorts.