Abstract
Background: Growing evidence suggests that leptin is critical for glycemic control. Impaired leptin signaling may also contribute to low adiponectin expression in obese individuals. We assessed the association of leptin and adiponectin with incident type 2 diabetes (T2D), their interactions with sex and obesity status, and mediation by insulin resistance.Methods: Study participants from the Jackson Heart Study, a prospective cohort of adult African Americans in Jackson, Mississippi, included those free of T2D at the baseline Exam 1. Incident T2D was defined as new cases at Exam 2 or Exam 3. We created separate Cox regression models (hazard ratios per log-transformed ng/mL of leptin and adiponectin) with and without insulin resistance, HOMA-IR. Mediation by insulin resistance was analyzed. Several interactions were assessed, including by sex, HbA1c, and obesity.Results: Among 3,363 participants (mean age 53 years, 63% women), 584 developed incident T2D. Leptin was associated with incident T2D when modeled without HOMA-IR (HR=1.29, 95% CI=1.05-1.58). Among men, this positive association between leptin and T2D was significant (HR=1.33, 95% CI=1.05-1.69), but it was nonsignificant among women (HR=1.24, 95% CI=0.94-1.64); statistical interaction with sex was nonsignificant (p=0.65). The associations in all participants and in men were nullified by HOMA-IR (HR=0.99, 95% CI=0.80-1.22; HR=1.00, 95% CI=0.78-1.28, respectively), indicating mediation through insulin resistance (proportion mediated: 1.04), and were not observed in abdominally obese participants. Adiponectin was inversely associated with T2D even after adjustment for HOMA-IR in women (HR=0.68, 95% CI=0.55-0.84), but not in men (HR=0.80, 95% CI=0.62-1.04). The inverse association was present only among abdominally obese participants, and persisted after adjustment for HOMA-IR.Conclusions: Among African Americans in the Jackson Heart Study the association of leptin with incident T2D was explained by HOMA-IR. The association of leptin and incident T2D was mediated by insulin resistance and observed only among abdominally non-obese. Differences by sex appeared: men showed a significant association mediated by insulin resistance. Among abdominally obese participants, adiponectin was inversely associated with incident T2D even after adjustment for HOMA-IR.
Egg consumption and risk of type 2 diabetes among African Americans: The Jackson Heart Study