Adiposity and Cortisol Regulation during Daily Living and Exercise in Adolescents with and without Down syndrome.

Abstract

Down syndrome (DS) is the most common genetic form of intellectual disability. Overweight and obesity are highly prevalent among individuals with DS, representing a health disparity relative to the general population. Research on obesity in DS is limited by reliance on body mass index (BMI) to describe and classify this health condition. Measuring adiposity with dual-energy x-ray absorptiometry (DXA) allows for three-compartment analysis including estimates of regional body composition and provides a better representation of adiposity in this unique population. Factors that contribute to the higher prevalence of obesity in DS are not well understood, yet are critical for designing health promotion interventions to address this condition in DS. The dissertation examined the associations between health behaviors (i.e. physical activity, dietary energy intake), cortisol, and adiposity in adolescents with and without DS. Three studies were conducted. The first described adiposity using DXA and examined associations with physical activity and dietary energy intake. The second and third studies examined cortisol, including diurnal patterns and responses to exercise, and associations with adiposity. The first study found significantly higher levels of body fat among adolescents with DS, particularly in the trunk region. However, the magnitude of difference compared to typically developing adolescents was considerably smaller than when examined with BMI, suggesting that BMI may be overestimating obesity in DS. Physical activity showed a moderate association with adiposity. The second study found that diurnal cortisol patterns were not significantly different between adolescents with and without DS. Differences in cortisol levels were observed between adolescents when stratified by the interaction of total body fatness and physical activity, indicating a joint effect on the association with adiposity. The third study attempted to compare the cortisol response to exercise between adolescents with and without DS, but neither group demonstrated a significant response. When stratified by total body fatness, cortisol levels were moderately higher in adolescents with greater adiposity. These higher cortisol levels may help to partially explain levels of adiposity in adolescents with DS. Due to the high levels of obesity and low levels of physical activity, directed health promotion interventions are needed in this population.