Bi-directional relationship between obesity and depression among adolescent girls
Major depressive disorder is one of the most common mental health conditions in the world while obesity, a condition tied to numerous chronic conditions throughout the lifespan, is at epidemic levels throughout most of the world. Adolescence is a crucial transition period for physical, cognitive, and social-emotional development. Adolescents, particularly girls, are at high risk of developing depression and obesity. Some studies suggest that obesity is a risk factor for the development of depression while others suggest that depression alters health habits, thereby leading to obesity. The overall goal of this work is to examine both of these questions in adolescent girls and further to explore whether the relationship between obesity (and other related risk factors) and depression is a bi-directional one. The National Heart, Lung, and Blood Institute's Growth and Health Study (NGHS) is an observational study of 2379 adolescent black and white girls. Height and weight was measured annually (and used to estimate body mass index) over 10 years from early to late adolescence. Diet and other risk factors were also measured longitudinally over 10 years. Depression was measured twice using the Centers for Epidemiologic Studies Depression Scale (CES-D): first at exam 8 and then at the final exam (exam 10). Multivariable logistic regression and longitudinal (repeated measures) mixed models were used to control for potential confounding by age, socio-economic status, physical activity, hours of television/video watching per day, and dietary factors. The first objective was to determine whether young adolescent girls who were already overweight or obese had a higher risk for developing depression during the follow-up exams in later adolescence. Overall, the prevalence of moderate (or worse) depression was much higher in girls who were classified as obese (474% with depression) than either overweight (37.8%) or normal-weight (34.3%) girls. After adjusting for baseline age, race, SES, television/video hour per day), physical activity level, diet quality (using Healthy Eating Index scores), and percent of energy from protein, obese girls had a 68% increase risk of subsequent depression (95% CI: 1.17 to 2.39) compared with normal weight girls. There was no increased depression risk for overweight girls. The risk of incident depression associated with obesity was the same for blacks and whites in the study. Finally, after controlling further for a measure of self-worth (using the Harter Scales), the effect of obesity was somewhat attenuated. The second objective of the study was to explore other risk factors for depression in these adolescent girls. In these analyses, several factors from the early adolescent years predicted the development of later depression (moderate or worse). These included hours spent watching television (risk increased by 6% for each additional hour watched per day), white race, SES, obesity, and self-worth score. While the self-worth score ranged only from 1 to 4, there was nearly a 60% reduction in risk for each increase of one point in the score. Thus, self-worth was a particularly important predictor, with higher self-worth scores protecting these girls from incident depression. The final objective of this work was to examine the change in behavioral risk factors associated with prevalent depression at exam 8. Depressed (vs. non-depressed) girls who were not obese at exam 8 were approximately 75% more likely to become obese by exam 10. The results of this study support a finding of a bi-directional relationship between obesity and depression in adolescent girls.