[Observation of sequential changes in results of oral glucose tolerance tests in individuals]

Using data from a series of health examination tests for members and their family of all agricultural cooperative associations in Hiroshima Prefecture during a fifteen year period from 1975 to 1989, sequential changes of the results of oral glucose tolerance tests in each year interval from 1 to 5 were studied for about 4300 individuals who participated in testing at least two times during the period. For those classified as normal on one test, the proportion of those who met the criteria of diabetes mellitus in 1 to 5 years later was less than one percent for both male and female. The changing rates from borderline or impaired glucose tolerance (IGT) to diabetes 1 to 5 years later were higher than the rates from normal to diabetes with the rate from borderline to diabetes one year later being 1.0 percent and IGT to diabetes 13.3 percent for males, and 0.8 percent and 6.4 percent respectively for females. The changing rates from non-diabetes to diabetes were higher for males than for females and were higher for the older age group than for the younger group. The rates from borderline and IGT to diabetes increased with longer interval but did not parallel the increase in time interval. For those classified as having diabetes on one test, the proportion of those classified as diabetic again in later years was around 60 percent and independent of length of interval years. From those results it appears that reporting the changing rate from non-diabetes to diabetes in one year by WHO diabetes criteria as the incidence of diabetes may be inappropriate.