Diurnal cortisol profiles in autistic adolescents and young adults: Associations with social difficulties and internalizing mental health symptoms

Several autism-related characteristics, such as social difficulties, may contribute to high perceived stress and increased exposure to stressful life events in some autistic individuals. Repeated exposure to stress might lead to the dysfunction of the hypothalamic-pituitary-adrenocortical-axis and be a vulnerability factor for developing mental health difficulties. Previous studies show contradictory findings on salivary cortisol in autism. In the current study, we investigated diurnal cortisol profiles in autistic adolescents and young adults, as well as their associations with social difficulties, stress exposure, and mental health symptoms. Autistic (n = 48, Mage = 17.6) and nonautistic (n = 51, Mage = 18.4) participants collected salivary cortisol at home six times a day for 2 days. Social difficulties, exposure to stressful life events/bullying, and mental health symptoms were assessed with questionnaires and clinical interviews. Similar diurnal cortisol slopes (DCS) and cortisol awakening responses were observed between the groups, but autistic participants showed higher total cortisol output (AUCG, area under the curve with respect to ground) during the day (b = 19.09, p = 0.009). In the autistic group, more severe social difficulties were associated with flatter DCS (b = 0.01, p = 0.007). Finally, cortisol alterations were associated with self-reported mental health symptoms, especially in autistic females in analyses uncorrected for multiple comparisons. In conclusion, our results do not indicate autism-related group-level alterations in most diurnal cortisol measures, but autistic youth showed higher total cortisol (AUCG) compared with nonautistic peers. More detailed investigation of interindividual variability in cortisol profiles within autistic people might give us important insights into vulnerability to developing stress-related mental health difficulties. Cortisol is a glucocorticoid hormone the levels of which fluctuate following the body's daily rhythm over a 24-hour cycle (i.e. circadian rhythm). Cortisol levels can also be altered due to perceived stress or other factors. We investigated whether daily cortisol rhythms differ in autistic and nonautistic adolescents and young adults. Most daily cortisol measures did not differ between the groups, but autistic youth showed higher cortisol levels than nonautistic youth. Moreover, in autistic participants, more severe social difficulties were associated with greater fluctuation in cortisol throughout the day. More detailed investigation of the observed variability in cortisol rhythms might help us to understand the vulnerability to stress-related mental health difficulties.