Impaired glucose tolerance, along with impaired fasting glucose (IFG), is recognized as being a stage in the transition from normality to diabetes. Thus, individuals with IGT are at high risk of progressing to type 2 diabetes, although such progression is not inevitable, and probably over 30% of individuals with IGT will return to normal glucose tolerance over a period of several years.
The decision to include data on IGT was based on two major factors associated with its presence: it greatly increases the risk of developing diabetes 1 , and it is associated with the development of cardiovascular disease 2 3 . In addition, some of the best evidence we have on the prevention of type 2 diabetes comes from studies in people with IGT.
It is estimated that some 344 million people worldwide, or 7.9% in the age group 20-79, will have IGT in 2010, the vast majority of whom live in low- and middle-income countries. By 2030 the number of people with IGT is projected to increase to 472 million, or 8.4% of the adult population.
As with diabetes, the 40-59 age group is expected to have the greatest number of people with IGT with 138 million for 2010, and this will remain true in 2030 with 186 million as shown in Figure 2.3. It is also of note that nearly one-third of all those who will have IGT for 2010 are in the 20-39 age group (see Figure 2.3).
The prevalence of IGT is generally similar to that of diabetes, but somewhat higher for the African and Western Pacific Regions, and slightly lower in the North America and Caribbean Region.
Map 2.3 Prevalence* (%) estimates of impaired glucose tolerance (20-79 years), 2010
1: Shaw JE, Zimmet PZ, de Courten M, et al. Impaired fasting glucose or impaired glucose tolerance. What best predicts future diabetes in Mauritius? Diabetes Care 1999; 22 (3): 399-402.
2: Perry RC, Baron AD. Impaired glucose tolerance. Why is it not a disease? Diabetes Care 1999; 22 (6): 883-885.
3: Tominaga M, Eguchi H, Manaka H, et al. Impaired glucose tolerance is a risk factor for cardiovascular disease, but not impaired fasting glucose. The Funagata Diabetes Study. Diabetes Care 1999; 22 (6): 920-924.