In 70 middle-class mothers of 2-year-old children, individual differences in mothers' morning cortisol levels, cortisol decreases across the day and average cortisol levels were predicted from demographic and medical control variables, maternal relationship functioning and home and work demands. For two days, salivary cortisol levels were measured in the morning immediately after wakeup, four times in the afternoon, and in the evening immediately prior to bedtime. Hierarchical linear modeling (HLM) growth curve analyses were used to estimate the intercept (early morning level), slope (steepness of decline in cortisol values across the day), and the average height of each mother's cortisol curve across the waking hours. HLM and multiple regression techniques were then used to predict individual differences in these parameters from the variables of interest. Time of day accounted for 72% of the variation in mothers' observed cortisol values across the day. After controlling for demographic and medical variables, positive relationship functioning was associated with higher mornings cortisol levels and a steeper decline in cortisol across the day, while greater hours of maternal employment and a greater number of children in the household were associated with lower morning cortisol values and a less steep decline in cortisol levels across the day. Variables predicting higher morning values also predicted higher average cortisol levels, while variables predicting lower morning cortisol predicted lower average cortisol levels. The full model including selected control, relationship functioning and home and work demand variables accounted for 40% of the variance in mothers' morning cortisol values, 43% of the variance in cortisol slopes and 35% of the variability in mothers' average cortisol levels. This study presents the first evidence of associations between psychological variables and individual differences in the organization of cortisol levels across the waking day in normal adult women. (C) 2001 Elsevier Science Ltd. All rights reserved.
