It has been suggested that the metabolic syndrome and type 2 diabetes are manifestations of the inflammatory host response. This host response is orchestrated by the production of pro- and anti-inflammatory cytokines that are under genetic control. We therefore hypothesized that a low production capacity of interleukin-10 (IL-10), a centrally operating cytokine with strong anti-inflammatory properties, associates with the metabolic syndrome and type 2 diabetes in old age. In the current study, 599 inhabitants of the city of Leiden, age 85 years, were visited at their place of residence. The production capacity of the anti-inflammatory cytokine IL-10 was assessed in a whole-blood assay in which lipopolysaccharide was used as a stimulus. Serum concentrations of lipids, lipoproteins, glucose, and HbA(1c) were determined, and a history of type 2 diabetes was obtained. Serum concentrations of total cholesterol, LDL cholesterol, triglycerides, glucose, and HbA(1c) gradually decreased over strata representing higher IL-10 production capacity, whereas the concentration of HDL cholesterol gradually increased (all P < 0.01). The odds ratio for type 2 diabetes was 2.7 (95% confidence interval 1.5-4.9) when subjects with the lowest IL-10 production capacity were compared with those with the highest IL-10 production capacity. These findings showed that low IL-10 production capacity (i.e., a pro-inflammatory response) is associated with the metabolic syndrome and type 2 diabetes.