A mid-day surge in cortisol levels.

A dramatic mid-day surge of cortisol with its onset concomitant with food intake was observed. Cortisol levels were unaffected by the evening meal. The magnitude and time course of the initiation of this mid-day peak of cortisol are markedly attenuated by food deprivation. These observations establish that within the circadian periodicity there exists a mid-day rhythm of cortisol secretion which appears to be synchronized by food intake.