Context: Persons with impaired glucose tolerance (IGT) are known to have an elevated risk of developing diabetes mellitus. Less is known about diabetes risk among persons with impaired fasting glucose (IFG) or with normal glucose levels.

Objective: To determine the incidence of diabetes in relation to baseline fasting and postload glucose levels and other risk factors.

Design, setting, and participants: Population-based cohort study conducted from October 1989 to February 1992 among 1342 nondiabetic white residents of Hoorn, the Netherlands, aged 50 to 75 years at baseline, in whom fasting plasma glucose (FPG) levels and glucose levels 2 hours after a 75-g oral glucose tolerance test were measured at baseline and at follow-up in 1996-1998.

Main outcome measures: Cumulative incidence of diabetes, defined according to the diagnostic criteria of the World Health Organization (WHO-1985 and WHO-1999) and the American Diabetes Association (ADA-1997), during a mean follow-up of 6.4 years, compared among participants with IFG, IGT, and normal glucose levels at baseline.

Results: The cumulative incidence of diabetes was 6.1%, 8.3%, and 9.9% according to the WHO-1985, ADA, and WHO-1999 criteria, respectively. The cumulative incidence of diabetes (WHO-1999 criteria) for participants with both IFG and IGT was 64.5% compared with 4.5% for those with normal glucose levels at baseline. The odds ratios for diabetes (WHO-1999 criteria), adjusted for age, sex, and follow-up duration, were 10.0 (95% confidence interval [CI], 6.1-16.5), 10.9 (95% CI, 6.0-19.9), and 39.5 (95% CI, 17.0-92.1), respectively, for those having isolated IFG, isolated IGT, and both IFG and IGT. In addition to FPG and 2-hour postload glucose levels (P<.001 for both), the waist-hip ratio also was an important risk factor for developing diabetes (P =.002).

Conclusion: In this study, the cumulative incidence of diabetes was strongly related to both IFG and IGT at baseline and, in particular, to the combined presence of IFG and IGT.