Circadian body temperatures and the effects of a cold stress in elderly and young subjects.

To determine whether there is a decrement in normal resting body temperature with age, 11 healthy elderly and 11 young adults were studied together for 48 h in warm (21 degrees C) ambient conditions. The resting levels and daytime rhythms of urine and oral temperature were similar, but night-time body temperature fell to a lower value in the young. There were time-of-day effects of increasing skin temperature and metabolic rate in both groups with resting levels higher in the young. After 6 h in cold (6 degrees C) conditions, core (urine) temperature fell by 0.4 degrees C in the elderly subjects but was maintained in the young, and the rise in blood pressure in the elderly exceeded that in the young. Self-reported arousal, however, increased equally in both groups in the cold.