Lack of association between body mass index and plasma adiponectin levels in healthy adults

Objectives: To test the hypothesis that obesity (increase in fat mass) independently affects the level of adipokines: adiponectin, tumor necrosis factor-α (TNFα) and interleukin (IL)-6. Methods: Publications in the past decade reporting adult plasma adiponectin, leptin, TNFα and/or IL-6 levels were compiled. Mean gender-specific values were extracted from studies that included medical screening to confirm physical health (43 groups, total 4852 subjects). Correlation analysis was conducted between adipokine levels and body mass index (BMI), a widely used estimate of adiposity. Results: For healthy lean to obese adults of both genders, no significant correlation between plasma adiponectin and BMI was detected. There was also no gender difference in plasma adiponectin level. In contrast, leptin levels showed a positive correlation with BMI in both genders, and women had significantly higher levels of plasma leptin consistent with a higher percentage of body fat. The proinflammatory cytokine TNFα failed to show correlation with BMI. Although IL-6 showed a positive correlation with BMI in women, the obesity-related increase was very limited. Conclusions: Data analysis based on studies performed on healthy adults did not support the hypothesis that obesity independently affects the plasma level of adiponectin and TNFα. Reported obesity-related changes in plasma adipokine levels may be a consequence of obesity-related metabolic disorders. Future studies are especially needed to understand the homeostasis of adiponectin.