The combined association of depressive symptoms and C-reactive protein for incident disease risk up to 12 years later. Findings from the English Longitudinal Study of Ageing (ELSA)

Background: Depression and inflammation are interrelated, and both are associated with the development of long-term conditions (LTCs). We investigated whether the combination of elevated depressive symptoms and elevated C-reactive protein (CRP) was associated with the rate of onset of a range of LTCs. Methods: We analysed data from 5360 participants (65.77 +/- 9.46 years; 54.1% female) from the English Longitudinal Study of Ageing (ELSA). Depressive symptoms were indicated using the Centre for Epidemiological Studies Depression (CES-D) scale and scores were combined with high sensitivity (hs)-CRP values to reflect the additive interaction between low/high depressive symptoms (CES-D >= 4) and low/high CRP (> 3mg/L). Participants were followed-up for up to 12 years to predict incident illness. Cox proportional hazard regression was used controlling for covariates. Results: In fully adjusted models, the combination of elevated depressive symptoms and elevated CRP was an independent predictor of coronary heart disease (CHD) (HR = 1.68, 95% C.I. = 1.01-2.78), stroke (HR = 2.02; 95% C.I. = 1.48-2.76), diabetes/high blood glucose (HR = 1.69; 95% C.I. = 1.11-2.57), and pulmonary disease (HR = 1.79; 95% C.I. = 1.02-3.15) relative to low depressive symptoms/low CRP, independently of age, sex, wealth, cohabitation, smoking status, body mass index and hypertension. Elevated depressive symptoms and low CRP was associated with arthritis incidence (HR = 1.49; 95% C.I. = 1.15-1.92). No association was found for cancer incidence. Conclusion: A combination of depressive symptoms and CRP was implicated in the onset of CHD, stroke, diabetes/high blood glucose, and pulmonary disease up to 12 years later, reflecting the role of psychobiological processes across multiple disease states.