Insulin Resistance and Obesity and their Association with Depression in Relatively Young People: Findings from a Large U.K. Birth Cohort

Background Depression frequently co-occurs with dysglycaemia and obesity. Low-grade systemic inflammation and lifestyle factors in childhood may predispose to dysglycaemia, obesity and depression. We aimed to investigate the cross-sectional and longitudinal associations between dysglycaemia, obesity and depression, and to examine the effect of demographics, lifestyle factors and antecedent low-grade inflammation on such associations in young people. Methods Using the Avon Longitudinal Study of Parents and Children (ALSPAC) birth cohort, we used regression analyses to examine: 1) cross-sectional; and 2) longitudinal associations between measures of dysglycaemia (Insulin Resistance (IR); impaired glucose tolerance (IGT)) and body mass index (BMI) at ages 9 & 18 years, and depression (depressive symptoms (DS) and depressive episode (DE)) at age 18 years; and 3) whether sociodemographics, lifestyle factors or inflammation (interleukin-6 (IL-6) at age 9 years) confounded any such associations. Results We included 3,208 participants. At age 18 years, IR and BMI were positively associated with depression. These associations may be explained by sociodemographic and lifestyle factors. There were no longitudinal associations between dysglycaemia/BMI and depression, and adjustment for IL-6 and CRP did not attenuate associations between IR/BMI and depression; however, the longitudinal analyses may have been underpowered. Conclusions Young people with depression show evidence of dysglycaemia and raised BMI, which may be related to sociodemographic and lifestyle effects such as deprivation, smoking, ethnicity and gender. In future, studies with larger samples are required to confirm this. Preventative strategies for the poorer physical health outcomes associated with depression should focus on malleable lifestyle factors. Keywords Depression, overweight, obesity, insulin resistance, inflammation, dysglycaemia, ALSPAC