Association Between Objectively Measured Physical Activity And Salivary Cortisol Levels In Adolescents With Neurodevelopmental Disorders

PURPOSE: Previous studies have identified irregularities in salivary cortisol levels, a key stress biomarker, in patients with neurodevelopmental disorders (NDD). However, little is known about the association of sedentary time (ST) and different levels of physical activity, e.g., light (LPA), moderate (MPA), moderate-to-vigorous (MVPA), and vigorous (VPA), with salivary cortisol levels (a biomarker of stress) in adolescents with NDD. METHODS: 151 adolescents with clinically diagnosed NDD (28 with autism, 48 with attention-deficit/hyperactivity disorder (ADHD), and 75 with comorbid ASD-ADHD) and aged between 12-17 years were recruited in Hong Kong. Saliva samples were collected in the afternoon using salivates. Device-based PA levels were measured using a tri-axial wrist-worn accelerometer. We employed Freedson’s cutoff points to categorize the ST and PA levels. Data were analyzed using bootstrapping regression models (bias-corrected method, n = 5 K), adjusted for age, sex, and body mass index (BMI). Accelerometer data were processed with ActiLife software. Cortisol levels were quantified using an enzyme immunoassay ELISA kit. Data analysis was conducted in R Studio. RESULTS: Significant positive associations were shown between ST and cortisol levels (β = 0.0003, 95% CI = 0.00004 to 0.0006, p = 0.041) and a reverse association between VPA and cortisol levels in adolescents with ASD-ADHD (β = -0.005, 95% CI = -0.001 to -0.0001, p = 0.046). Among adolescents with ASD, MPA was positively associated with cortisol levels, although this was not statistically significant. In female adolescents with ADHD, cortisol levels were positively associated with LPA (β = 0.0007, 95% CI = 0.0001 to 0.0012, p = 0.017). CONCLUSION: The results of this study demonstrated the relationship between ST and PA levels with salivary cortisol levels in adolescents with ADHD and comorbid ASD-ADHD. Participation in PA programs may be essential for mitigating stress in this population. This study was funded by General Research Fund from Research Grants Council of Hong Kong (#14619720).