Serum Levels of Interleukin-6 and C-reactive Protein Correlate with Body Mass Index Across the Broad Range of Obesity

Background: It has been noted that elevated inflammatory markers, such as tumor necrosis factor-alpha (TNF), soluble TNF receptor II (sTNF-RII), interleukin 6 (IL-6) and C-reactive protein (CRP), are characteristically found in the serum in obese patients. In this study, we examined the correlation of these markers with BMI in nonobese, obese, and morbidly obese individuals to explore this relationship across the broad range of obesity.

Methods: A total of 9 nonobese, including normal and overweight (body mass index [BMI] <30 kg/m2) and 41 obese (BMI > or =30 kg/m2) adults were included in this study. Among obese subjects, 11 subjects were grade I or II obese (BMI > or =30 and <40 kg/m2), and 30 subjects were morbidly obese (grade III obese, BMI > or =40 kg/m2). Serum levels of glucose, insulin, TNF, sTNF-RII, IL-6, and CRP were measured.

Results: Obese subjects (BMI > or =30 kg/m2) had significantly higher serum levels of TNF, sTNF-RII, IL-6, and CRP compared with nonobese subjects. Serum levels of sTNF-RII, IL-6, and CRP, but not TNF, were positively correlated with BMI in obese subjects. However, in morbidly obese subjects, only the serum concentrations of IL-6 and CRP remained correlated with BMI, primarily because of this relationship in men.

Conclusions: The present results support evidence that obesity represents an inflammatory state. In morbid obesity, the correlation of only IL-6 and CRP with BMI, particularly in males, suggests that IL-6 may be secreted in an endocrine manner in proportion to the expansion of fat mass particularly in the abdominal region, with a corresponding increase in hepatic production of CRP.