Association between C-reactive protein levels and mortality risk in older workers and non-workers

Objectives: The positive effects of employment on older worker mortality can be attenuated by various health and environment-related factors. C-reactive protein (CRP) is a non-specific indicator of inflammation exposure. We compared mortality risk in older workers and non-workers across measured levels of CRP. Methods: Using pooled 1988-1994 National Health and Nutrition Examination Survey III data with mortality follow-up through 2006 from the National Death Index, age-adjusted mortality rates for U.S. individuals aged >=65 years were examined. Hazard ratios were calculated for workers and non-workers by CRP levels: 1) low (<0.33 mg/dL); 2) high (>=0.33 mg/dL). Results were adjusted for race/ethnicity, health status, age, and gender. Results: Classification of 3,618 participants aged 65+ was: 1) low-CRP non-workers (n=1,900); 2) high-CRP non-workers (n=1,252); 3) low-CRP workers (n=309); and 4) high-CRP workers (n=157). We identified 2,596 deaths. Compared to the low-CRP non-workers group, the high-CRP non-workers individuals were at highest risk of mortality (Hazard Ratio: 1.18; 95% Confidence Interval: 1.05–1.31), and low-CRP workers were at lowest risk (0.57; 0.44-0.73). High-CRP workers were not significantly different from either non-worker group; however they were at higher risk of mortality compared to low-CRP workers (1.75; 1.22-2.51). Higher risk was also associated with male gender (1.62; 1.56-1.69), fair/poor health (1.58; 1.38-1.80), and white non-Hispanic race/ethnicity (1.34; 1.06-1.69). Conclusions: Employment at an older age was associated with lower mortality risk for low CRP levels, but not for high CRP levels. CRP can be used as a non-invasive way to monitor mortality risk across older population groups.