Research has suggested that daytime cortisol secretion levels in children with autism may be higher compared to typically developing children. In addition, there is some evidence for higher cortisol secretion levels as a result of poor sleep hygiene in young children.

Fifty-two subjects (26 children with autism (AUT) and 26 typically developing children (TYP)) from 2 to 5 ½ years of age were recruited from the Sacramento region. Cortisol was obtained from saliva at waking, midday, and bedtime on two consecutive days at three phases (baseline, 3 months later, 6 months later). Sleep measurement was acquired from actigraphy over 7 days and nights at each phase. G-computation estimation and linear mixed models were used for the primary analyses.

At waking, AUT had a mean level of cortisol of 8.29 (95%CI 6.99, 10.51) nmol/liter and TYP of 6.95 (95%CI 5.97, 8.49) nmol/liter. The variability in the slope of cortisol for AUT (0.0214, 95%CI 0.0066, 0.0362) was 3 ½ times that of TYP (0.0061, 95%CI -0.0041, 0.0164). The between-subject variance estimate for AUT (0.0663, 95%CI 0.0148, 0.1178) was 1 ½ times that of TYP (0.0388, 95%CI 0.0021, 0.0756). There was also a graded response among AUT by functional status - cortisol secretion levels increased as IQ decreased.

There were also differences for some of the sleep parameters. The difference at the morning or waking sampling was 3 nmol/liter for 100 minutes awake compared to no waking during the night (95% CI for difference: -0.23, 7.69). The cortisol mean at the waking sampling was higher (13.6 nmol/liter) for a child with a night-waking problem compared to a child without a night-waking problem (7.4 nmol/liter) (95% CI for difference: -0.55, 9.35).

The Sleep and Cortisol Study has contributed to the current literature by establishing average cortisol secretion values at waking, midday, and bedtime in preschool-aged AUT and TYP. Important differences were observed in cortisol variability in AUT compared to TYP and in cortisol secretion by functional status. Novel results for cortisol secretion at waking and the association with being awake and night-waking need replication in future studies.