Objective: Levels of adiposity-signaling hormones and inflammatory markers are less favorable in individuals with the metabolic syndrome; their role in the association between the metabolic syndrome and cardiovascular mortality remains unclear.
Research design and methods: We conducted a prospective study of 977 men and 1,141 women aged 40-94 years in 1984-1987, followed for mortality for a maximum of 20 years. Adiponectin, leptin, ghrelin, interleukin-6 (IL-6), C-reactive protein (CRP), and Adult Treatment Panel III-defined metabolic syndrome components were measured in fasting blood samples obtained in 1984-1987. Cox-proportional hazards models were used in survival analyses.
Results: The age- and sex-adjusted hazard ratio (HR) (95% CI) for coronary heart disease (CHD) mortality associated with the metabolic syndrome was 1.65 (1.25-2.18) (P < 0.001); this association did not differ significantly by sex, age, or diabetic status (P > 0.2 for each interaction). The association between the metabolic syndrome and CHD mortality was not materially changed after adjustment for adiponectin, leptin, and ghrelin; it was attenuated by 25% after adjustment for IL-6 and 35% after adjustment for CRP. CHD mortality increased linearly with greater levels of IL-6 and CRP (P(trend) < 0.001 for each); the age- and sex-adjusted HRs comparing highest versus lowest quarter were 3.0 (1.87-4.89) for IL-6 and 2.1 (1.41-3.21) for CRP. IL-6, but not CRP, remained a significant predictor of CHD mortality in models including both inflammatory markers and the metabolic syndrome.
Conclusions: Adiposity-signaling hormones and inflammatory markers explain little to some of the association between the metabolic syndrome and CHD mortality. IL-6 levels predict CHD mortality independently of CRP.