Effects of Chronotype on Sleep Duration and Body Composition Variables

Body composition changes with age. These changes include decreases in fat-free mass and increases in fat mass and central fat accumulation. Improving body composition will augment efforts to lower obesity rates and cardio-metabolic diseases (e.g. type 2 diabetes). Sleep may be a determinant of body composition, whereby shortened sleep duration predicts weight gain. However, evidence is inconsistent. Differences in chronotype (the extent to which an individual is a ?morning? or an ?evening? person) may explain these inconsistent findings. This study will examine the extent to which chronotype modifies the association between sleep duration, fat mass, and fat-free mass in adults. Obesity is associated with leading causes of death and chronic disease (e.g. cardiovascular disease). To elucidate the relationship between obesity and sleep, this study will explore sleep duration, with an emphasis on chronotype-specific differences in eating habits, physical activity, fat mass, and fat free mass. This is aligned with the UK Biobank?s purpose because if chronotype modifies the relationship between sleep and obesity, it may be used to predict who is at greatest risk for obesity onset. These findings may also provide insight into chronotype based weight management interventions. We will examine the hypothesis that chronotype modifies the effect between sleep duration and obesity. Obesity will be regressed on the indicator for whether or not someone is a ?morning? person or an ?evening? person and sleep duration to determine this relationship. Then to determine potential causal pathways through which sleep duration impacts body composition, chronotype-specific differences in eating habits, physical activity, and body composition will be quantified using structural equation modeling. This approach will allow us to quantify the relationship of other potentially influential variables such as person, demographic, and environmental factors. Data from the full UK Biobank cohort, stratified and balanced on sex, will be used to elucidate the relationship between chronotype, sleep duration and body composition.