INDIVIDUAL-DIFFERENCES IN THE DIURNAL CYCLE OF CORTISOL

This study investigated individual differences in the diurnal cycle of cortisol and explored their relation to several psychosocial variable s and to upper-respiratory symptoms. Cortisol and daily experience wer e assessed for 2 days in 109 healthy employed and unemployed community residents (mean age = 36.4 +/- 12.1, 69% female); self-report upper r espiratory illness (URI) symptoms were assessed for an additional 10 d ays. Fifty-six (51%) participants showed typical declines in cortisol during both days, 19 (17%) showed no significant diurnal pattern on bo th days, and 34 (31%) showed different diurnal patterns on the 2 days. Individuals with no cycles did not differ from those with normal or i nconsistent cycles on demographic factors, baseline psychological meas ures, health behaviors, or daily experiences over the two assessment d ays. Individuals without cortisol cycles, however, reported fewer URI symptoms than the remaining subjects. That 17% of our sample did not e xhibit diurnal cycles of cortisol was surprising, given established vi ews of normal endocrine function. Although average daily level of cort isol is related to a number of psychosocial and psychiatric factors (e .g. stress and depression), pattern of diurnal cycle was not related t o any demographic or psychosocial measures in this study. The finding that flat cycles were related to fewer reports of URI symptoms suggest s that perturbations in cycle may be related to processes associated w ith symptom susceptibility or symptom expression. (C) 1997 Elsevier Sc ience Ltd.