Original Article The Intrauterine Environment as Reflected by Birth Size and Twin and Zygosity Status Influences Insulin Action and Intracellular Glucose Metabolism in an Age- or Time-Dependent Manner

According to the “fetal origins hypothesis, ” monozygotic (MZ) twins may be more prone to develop various meta-bolic abnormalities compared with dizygotic (DZ) twins, and twins all together may be more predisposed to meta-bolic defects compared with singletons. To determine the impact of twin and zygosity status as well as birth size on in vivo measures of glucose metabolism, we examined 123 young (aged 22–31 years) and 103 elderly (aged 57–66 years) MZ and DZ twins and age-matched singleton control subjects. All participants were born at term with available birth records. Peripheral and hepatic insulin action and intracellular glucose partitioning was determined by a euglycemic-hyperinsulinemic clamp using tritiated glucose combined with indirect calorimetry. In elderly subjects, zygosity status influenced nonoxidative glucose metabo