Introduction Depressive symptoms are associated with increased risk of incident diabetes. Inflammatory mechanisms have been suggested to be involved in depression and diabetes. Specifically, increased levels of C-reactive protein (CRP), a biomarker for inflammation, is associated with depression and have also been linked to risk of developing diabetes.

Objective To assess the association of both CRP and depressive symptomatology with diabetes incidence in a representative sample of English people ≥50 years old.

Methods Participants were 5475 community-dwelling men and women without diabetes at baseline from the English Longitudinal Study of Ageing (ELSA). Wave 2 of ELSA was used as baseline (first assessment of CRP), with assessment of diabetes incidence at waves 3, 4, and 5. Elevated depressive symptoms were based on a score ≥4 using the 8-item Center for Epidemiologic Studies Depression (CES-D) scale, and high CRP level was defined as >3 mg/L. Diabetes incidence was indicated by self-reported doctor diagnosis. Association of diabetes incidence with baseline CRP and depressive symptomatology groups was examined using multivariate logistic regression adjusted for socio-demographic, lifestyle, metabolic, and health variables.

Results In comparison to participants with normal CRP levels and low depressive symptoms, those with both high CRP and elevated depressive symptoms were more likely to develop diabetes over 6 years of follow-up (adjusted OR: 1.90, 95% CI: 1.10–3.30). Individuals with high CRP and low depressive symptoms (adjusted OR: 1.26, 95% CI: 0.89–1.78) and those with normal CRP and elevated depressive symptoms (adjusted OR: 1.55, 95% CI: 0.88–2.73) were not associated with diabetes incidence.

Conclusion People with high CRP and elevated depressive symptoms are more likely to develop diabetes. Further analyses will examine the possible interactions between CRP and depression with diabetes incidence.