The relationship between overweight and depression in view of genes, environment and their joint influence

Abstract: Obesity and depression are known to often go hand in hand, but is this due to our genetic heritage, environmental factors or a combination thereof? With a neuroscientific approach, I have investigated the relationship between obesity and depression with the aim of bridging the different levels of research available in order to better understand this complex topic. Using data from a longitudinal cohort with adults, we analysed the genetic contribution to antidepressant response in Study I. The association between antidepressant treatment and changes in body mass index, waist circumference and fat mass was assessed in Study II. In Study III, the importance of bullying victimization for the relationship between obesity and depression was analysed using a longitudinal cohort with adolescents. Lastly, the moderating effect from breastfeeding duration on the relation between a known obesity associated gene and body mass index among adolescents and young adults was examined in Study IV.The bidirectional relationship between obesity and depression is derived from several joint processes and mechanisms such as the stress system and symptomatology overlap with strong environmental influences affecting both disorders, plausibly through epigenetic processes. Even though overweight and obesity were associated with depressive symptoms, one even more important environmental factor for the development of symptoms was bullying victimization – a risk factor that persisted after six years of follow-up. The genetic contribution to these complex disorders from individual variations is small in most cases, but with a credible additive effect and with environmental factors as important moderators of these relationships. One such moderator is breastfeeding duration, which was found to contribute to the relationship between FTO and future BMI with different patterns for the individual variants, which supports the differential susceptibility hypothesis. Finally, when AD treatment is used, the patient should be monitored regularly, both regarding depressive symptoms as well as obesity-related measurements.Overall, it is of high importance to focus on prevention because the frequently chronic course of obesity, as well as depression, has a high burden on individuals, as well as on society.