Excess body weight and specific types of depressive symptoms: Is there a mediating role of systemic low-grade inflammation?

Objectives: Obesity is associated with an increased risk of depression. Systemic low-grade inflammation, a plausible consequence of obesity, has also been linked to depression. However, the potential mediating effects of systemic low-grade inflammation on the association between excess body weight and specific symptom domains of depression remain uncertain. This study examined whether systemic low-grade inflammation mediated the associations of excess body weight (overweight and obesity) with subsequent overall, cognitive-affective, and somatic depressive symptoms.Design: This study used a prospective cohort design.Methods: The final analytical sample included 4,942 adults aged >= 50 years drawn from the English Longitudinal Study of Ageing (ELSA). Body mass index (BMI) and covariates were ascertained at baseline (wave 4, 2008/09). Continuous BMI scores were divided into four categories: 'normal weight' (18.5 <= BMI <25 kg/m2); 'overweight' (25 <= BMI <30 kg/m2); 'obesity' (BMI >= 30 kg/m2); in addition to 'excess body weight' ('overweight' and 'obesity' combined). Covariates included sociodemographic variables, behavioural factors, and chronic physical conditions. Serum concentrations of CRP were measured at wave 6 (2012/13). Depressive symptoms were assessed at baseline and ten years later (wave 9, 2018/19), using the 8-item Centre for Epidemiological Studies Depression (CES-D) Scale. Two symptom domains were constructed, distinguishing between cognitive-affective (depressed mood, loneliness, sadness, enjoyment in life, and happiness) and somatic (sleep problems, low energy levels, and fatigue) symptoms. Mediation analyses were performed to examine whether CRP statistically medi-ated the associations between BMI categories and depressive symptoms.Results: In multivariable-adjusted analyses, excess body weight was associated with elevated somatic (OR = 1.231, 95% CI: 1.029, 1.473), but not cognitive-affective or overall depressive symptoms at follow-up. Higher CRP was associated with elevated somatic (OR = 1.156, 95% CI: 1.061, 1.259), but not cognitive-affective or overall depressive symptoms. CRP acted as a partial mediator (14.92%) of the association between excess body weight and elevated somatic, but not cognitive-affective, or overall depressive symptoms.Conclusion: Systemic low-grade inflammation may partially explain the association of excess body weight with somatic depressive symptoms, but not the associations with cognitive-affective or overall depressive symptoms.

Automated summary

This study aimed to investigate whether systemic low-grade inflammation mediated the association between excess body weight and different symptom domains of depression. The results showed that systemic low-grade inflammation partially mediated the association between excess body weight and somatic depressive symptoms, but not cognitive-affective or overall depressive symptoms.