Age-Related Glucose Intolerance Is Associated with Impaired Insulin Secretion in Community-Dwelling Japanese Adults: The Kumamoto Koshi Study

<b>Background/Objectives</b>: Glucose tolerance progressively declines with age. However, the effects of aging on insulin secretion and insulin sensitivity in Japanese subjects are unclear. <b>Methods</b>: We conducted an oral glucose tolerance test (OGTT) in residents aged between 22 and 85 years in Koshi City, Kumamoto Prefecture, Japan, to clarify the characteristics of insulin secretion and insulin sensitivity in older adults. Participants were recruited using a flyer, and the OGTT was performed after an overnight fast (12-16 h) between 8:00 and 10:30 am. <b>Results</b>: HOMA-IR and the Matsuda index are indices of insulin action. No correlation of age with HOMA-IR or the Matsuda index was found, whereas HOMA-β, the insulinogenic index, and the disposition index, all indices of insulin secretion, were negatively correlated with age in all participants and in individuals with normal glucose tolerance. Multiple regression analysis showed that age was an explanatory factor for insulin secretion. <b>Conclusions</b>: Impaired insulin secretion may contribute to age-related glucose intolerance in Japanese individuals.