Abstract
AIMS: To assess the impact of metabolic syndrome (MetS) on the incidence of type 2 diabetes in middle-aged Japanese individuals with impaired insulin secretion (IIS). METHODS: This cohort study included 1,702 individuals aged 40-59 without diabetes at baseline who underwent a comprehensive medical check-up between April 2008 and March 2009 at Saku Central Hospital. Participants were classified according to their IIS and insulin resistance (IR) status [normal, isolated IR (i-IR), or isolated IIS (i-IIS)] and MetS (presence or absence). They were followed up until March 2014. Type 2 diabetes was defined based on fasting and 2-h post-load plasma glucose concentrations and by the receipt of medical treatment for diabetes. RESULTS: During 7,572 person-years of follow-up, 92 individuals developed type 2 diabetes. The incidence rates (/1,000 person-years) for type 2 diabetes in the normal without MetS, normal with MetS, i-IR without MetS, i-IR with MetS, i-IIS without MetS, and i-IIS with MetS groups were 5.3, 3.7, 11.3, 24.7, 16.7, and 59.5, respectively. The multivariable-adjusted hazard ratios (HRs) and 95 % confidence intervals (CIs) for type 2 diabetes in the normal with MetS, i-IR with MetS, and i-IIS with MetS groups, relative to the normal without MetS group, were 0.52 (0.12-2.25), 3.78 (1.93-7.42), and 7.94 (3.96-15.91), respectively. Additionally, a positive association of MetS with type 2 diabetes was observed in the i-IIS group [HR (95 % CI) 3.56 (1.88-6.73)] but not in the normal and i-IR groups. CONCLUSIONS: The prevention of MetS is important, particularly in individuals with low insulin secretion.