Abstract
INTRODUCTION: A flatter diurnal cortisol curve has been associated with incident diabetes among older white adults. However, this relationship has not been examined among middle-aged individuals or African Americans [AA]. We analyzed the longitudinal association of baseline diurnal cortisol curve features with incident diabetes over a 10 year period in a cohort of AA and white participants who were, on average, 40 years old. METHODS: Salivary cortisol was collected immediately post-awakening, then subsequently 45 min, 2.5 h, 8 h, and 12 h later, as well as at bedtime. Cortisol curve features included wake-up cortisol; cortisol awakening response (CAR); early, late, and overall decline slopes; bedtime cortisol; and 16 -h area under the curve (AUC). Salivary cortisol (nmol/L) was log-transformed due to positively skewed distributions. Diabetes was defined as fasting plasma glucose ≥ 126 mg/dL or taking diabetes medication. Logistic regression models were used to investigate the association of log-transformed cortisol curve features with incident diabetes. The analysis was stratified by race and adjusted for age, sex, education, depressive symptoms, smoking status, beta-blocker and steroid medication use and BMI. RESULTS: Among 376 AA and 333 white participants (mean age 40 years), 67 incident diabetes cases occurred over 10 years. After full adjustment for additional covariates, a 1-unit log increase in CAR was associated with a 53 % lower odds of incident diabetes among whites (Odds Ratio [OR] 0.47, 95 % CI: 0.24, 0.90). A 1-SD increase in late decline slope was associated with a 416 % higher odds of incident diabetes among whites (OR 5.16, 95 % CI: 1.32, 20.20). There were no significant associations in AAs. CONCLUSION: A robust CAR and flatter late decline slope are associated with lower and higher odds of incident diabetes, respectively, among younger to middle-aged whites and may provide a future target for diabetes prevention in this population.