Background: Chronic obstructive pulmonary disease (COPD) is characterized by an irreversible chronic airflow obstruction and by an accelerated decline in lung function. Elevated circulating levels of C-reactive protein (CRP) and interleukin-6 (IL-6), both markers of systemic inflammation, have been found in COPD. Their possible associations with chronic airflow obstruction have mostly been evaluated in highly selected patient samples. Our objective was to evaluate the association between postbronchodilator lung function CRP and IL-6 in a randomly selected sample of the Icelandic population, 40 years and older, while adjusting for gender, age, smoking, and body weight.
Methods: Serum CRP and IL-6 values were measured among participants in the Burden of Obstructive Lung Disease (BOLD) study.
Results: Of the 938 subjects invited a total of 403 men and 355 women participated (response rate 81%) in the study. Their mean age (+/-SD) was 57.7 (+/-12.7) years. Both CRP and IL-6 were independently related to lower FEV1 and FVC values. Individuals in the highest quartiles of CRP and IL-6 had a 7.5% and 3.9%, respectively, lower FEV1% than predicted after adjustment for smoking, age, and body weight. High CRP levels were more strongly related to lower FEV1 levels in men (-11.4%) than in women (-0.4%).
Conclusions: In a random population-based sample both CRP and IL-6 were significantly related to lower spirometric values. The association with CRP was stronger in men than in women. This finding underscores the possible importance of systemic inflammation in irreversible airflow limitation.