A prospective evaluation of the directionality of the depression–inflammation relationship
Section snippets
Participants
Participants were 263 men and women enrolled in the Pittsburgh Healthy Heart Project (PHHP), a prospective study of healthy, community-dwelling adults aged 50–70 years. This study was approved by the University of Pittsburgh institutional review board. Participants provided written informed consent and were paid $700 for attending the baseline and 6-year visits. Details regarding recruitment and inclusion/exclusion criteria are provided elsewhere (Kamarck et al., 2007, Stewart et al., 2007).
Preliminary analyses
Bivariate correlations performed to examine the cross-sectional relationships among the factors of interest revealed that BDI-II was not associated with IL-6 (r = -0.01, p = 0.87) or CRP (r = -0.06, p = 0.36) at baseline. Similarly, 6-year BDI-II was not related to 6-year IL-6 (r = 0.03, p = 0.66) or CRP (r = 0.05, p = 0.41). Consistent with previous findings (Cesari et al., 2003, Luc et al., 2003), we observed moderate positive correlations between baseline IL-6 and CRP (r = 0.29, p < 0.01) and between 6-year
Discussion
The findings we report in this sample of healthy, older adults are most consistent with the notion that depression may lead to, rather than result from, augmented inflammation. Path analytic models revealed that greater depressive symptom severity at baseline was associated with larger 6-year increases in serum IL-6, even after adjustment for demographic, biomedical, and behavioral factors. Importantly, the magnitude of this relationship is not trivial; only one of the control variables, BMI,
Conflict of interest statement
All authors declare that there are no conflicts of interest.
Acknowledgments
This research was supported by the National Heart, Lung, and Blood Institute Grant HL056346 (TK, PI), Program Project Grant HL040962, and the Pittsburgh Mind-Body Center Grants HL076852 and HL076858. For their assistance with data collection, we thank the entire project staff of the Pittsburgh Healthy Heart Project.
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