Diabetes, depressive symptoms, and inflammation in older adults: results from the Health, Aging, and Body Composition Study

Abstract

Objective: Up-regulated levels of interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), and C-reactive protein (CRP) are common to both type 2 diabetes mellitus (T2DM) and elevated depressive symptoms, yet little attention has been given to the biological mechanisms associated with these co-morbidities. This study examined the association between inflammation and both T2DM and elevated depressive symptoms.

Methods: Baseline data were analyzed from 3009 adults, aged 70-79, participating in the Health, Aging, and Body Composition Study. Diabetes was assessed per self-report, medication use, fasting glucose and/or glucose tolerance tests. Elevated depressive symptoms were categorized using the Center for Epidemiologic Studies Depression scale (cut-score≥20). Log-transformed IL-6, TNF-α, and CRP were analyzed using ANCOVA.

Results: Participants with T2DM and elevated depressive symptoms (T2DM+DEP n=14) demonstrated significantly (p<.05) higher IL-6 compared to (T2DM Only n=628), (DEP Only n=49), and (No T2DM or DEP n=2067) groups following covariate adjustment. Similarly, participants with T2DM+DEP (n=14) had significantly (p<.05) higher CRP, after covariate adjustment, compared to DEP Only (n=50) and No T2DM or DEP groups (n=2153). No association was observed for TNF-α.

Conclusions: These findings provide evidence that inflammation is associated with T2DM and elevated depressive symptoms. Participants with T2DM+DEP demonstrated the highest IL-6 levels compared to all other groups. Greater CRP levels were also observed in T2DM, but not elevated depressive symptoms, which may suggest that differential associations between T2DM and depressive symptoms exist for various inflammatory markers. Further investigation into these associations could aid in understanding the biological pathways underlying both T2DM and depressive symptoms.

Keywords: C-reactive protein; Depressive symptoms; Diabetes; Inflammation; Interleukin-6; Tumor necrosis factor-α.

Conflict of interest statement

Competing Interests Statement

The authors have no competing interests to report and have no potential or real conflicts of interest to declare.

© 2013.

Figures

Figure 1

Adjusted marginal mean IL-6 (pg/mL) levels (±S.D.) according to diabetes and elevated depressive symptoms (CES-D ≥ 20) after controlling for age, race, gender, study site, percent body fat, smoking status, statin use, and heart and lung disease. Cell sizes may differ from the overall sample size due to variation in the availability of IL-6 and covariates for each participant. *p<.05 significant comparisons between T2DM + DEP and T2DM Only, DEP Only, and No T2DM or DEP groups. **p<.0001 significant comparison between T2DM Only and No T2DM or DEP groups.

Figure 2

Adjusted marginal mean CRP (mg/L) levels (±S.D.) according to diabetes and elevated depressive symptoms (CES-D ≥ 20) after adjustment for age, race, gender, percent body fat, triglycerides, smoking status, statin use, and lung disease. Cell sizes may differ from the overall sample size due to variation in the availability of CRP and covariates for each participant. *p<.05 significant comparisons between T2DM + DEP and DEP Only and No T2DM or DEP groups. There was also a significant comparison between T2DM Only and No T2DM or DEP groups.