Caregivers' hair cortisol: a possible biomarker of chronic stress is associated with obesity measures among children with disabilities

Background: The stress of caring for a loved one with chronic illness has been associated with childhood obesity. Hair cortisol has been proposed as a novel biomarker of chronic psychological stress. This study aimed to evaluate the associations between caregivers' chronic stress evaluated by hair cortisol concentrations (HCC) and obesity measures among children with disabilities such as autism. Methods: Eighty-five dyads of children with disabilities and their primary caregivers participated in the study between April and July 2013 in the Patagonia Region, Chile. Trained research staff conducted anthropometric measurements of children and caregivers. Cortisol concentrations, extracted from hair samples with methanol, were quantified using liquid chromatography tandem mass spectrometry. Pearson's correlation coefficients and linear regression models were used to examine the associations between caregiver HCC (log-transformed) and child obesity measures with adjustment for covariates. Results: Caregiver HCC were positively and significantly correlated with child weight (child age-and sex-adjusted r = 0.23, P = 0.036), body mass index (BMI) (r = 0.23, P = 0.035), circumferences of neck (r = 0.30, P = 0.006), waist (r = 0.27, P = 0.014), and hip (r = 0.22, P = 0.044). After adjustment for children's age and sex, caregiver HCC were significantly related to child weight (kg) (beta = 4.47, standard error (SE) = 2.09), BMI (kg/m(2)) (beta = 1.52, SE = 0.71), neck circumference (cm) (beta = 1.20, SE = 0.43), waist circumference (cm) (beta = 3.75, SE = 1.50), and hip circumference (cm) (beta = 3.02, SE = 1.48). Caregiver HCC were also positively but not statistically significantly associated with child waist-to-hip ratio (beta = 0.01, SE = 0.01; P = 0.191) or body fat percentage (%) (beta = 2.11, SE = 1.28; P = 0.104). Further adjustment for other covariates including child disability diagnosis and caregiver age, sex, education, current smoking, perceived stress, and caregiver BMI did not change the results substantially. Conclusions: Chronic stress of caregivers, evaluated by increased cortisol concentrations in hair, was positively associated with obesity measures among children with disabilities.