The joint subclinical elevation of CRP and IL-6 is associated with lower health-related quality of life in comparison with no elevation or elevation of only one of the biomarkers

BACKGROUND: Measures of health-related quality of life (HRQoL), like the Short Form (SF)-36, have been suggested to correlate with inflammatory biomarkers. It is, however, unclear whether a joint measure of two inflammatory biomarkers would bring additional information in comparison with evaluation of one inflammatory biomarker. OBJECTIVE: To evaluate associations between SF-36 and low-grade inflammation in a Swedish population, with emphasis on a combined measure of C-reactive protein (CRP) and interleukin-6 (IL-6) as a proxy for low-grade inflammation. METHODS: In a randomly selected sample of a middle-aged Swedish general population (n = 905; aged 45-69 years, 50% women), relations between SF-36 parameters and the biomarkers were tested. Regression and correlation analyses were adjusted for sex, age, presence of disease, lifestyle, and psychological factors. RESULTS: After adjustment for sex and age, HRQoL was significantly lower in the group with a joint elevation of CRP and IL-6 in comparison with either the group with no elevation or the groups showing elevation of one of the two biomarkers. Also after full adjustments, the combined measure of elevated CRP and IL-6, with few exceptions, was associated with significantly lower HRQoL in comparison with elevations in one of them, difference ranging from 4 (Mental Health scale) to 18 scale steps (Role-Physical scale). CONCLUSION: This study confirms that there is a relationship between HRQoL and low-grade inflammation. In particular, SF-36 scores are significantly lower in a group with joint elevation of IL-6 and CRP, in comparison with elevation of either one of them.