Abstract
CONTEXT: Multiple diseases may explain the association of the growth hormone/insulinlike growth factor-I (GH/IGF-I) axis with longevity. OBJECTIVE: To relate circulating GH/IGF-I system protein levels with major health events. DESIGN AND SETTING: This is a cohort study set in 4 US communities. PARTICIPANTS: Adults (N = 2268) 65 years and older free of diabetes and cardiovascular disease. MEASUREMENTS: We assessed insulinlike growth factor binding protein-1 (IGFBP-1) and ghrelin in fasting and 2-hour oral glucose tolerance test (OGTT) blood samples, as well as fasting IGF-I and IGFBP-3. Hazard ratios for mortality and a composite outcome for first incident myocardial infarction, stroke, heart failure, hip fracture, or death were adjusted for sociodemographic, behavioral, and physiological covariates. RESULTS: During 13,930 person-years of follow-up, 48.1% of individuals sustained one or more components of the composite outcome and 31.8% died. Versus the lowest quartiles, the highest quartiles of fasting and 2-hour ghrelin were associated with 27% higher (95% confidence interval [CI]: 6%, 53%) and 39% higher (95% CI: 14%, 71%) risks of the composite outcome, respectively. The highest quartile of 2-hour IGFBP-1 was associated with 35% higher (95% CI: 1%, 52%) risk of the composite end point. Similarly, higher mortality was significantly associated with higher fasting and 2-hour ghrelin levels and with 2-hour IGFBP-1 level. When examined together, 2-hour post-OGTT levels of IGFBP-1 and ghrelin tended to predict outcomes better than fasting levels. CONCLUSIONS: Circulating IGFBP-1 and ghrelin measured during an OGTT predicted major health events and death in older adults, which may explain the influence of the GH/IGF-I axis on lifespan and health.