The fact that glucose intolerance increases with age has been apparent for over 30 years, leading to the suggestion at one time that the diagnostic criteria for diabetes be amended to account for this inevitable consequence of the aging process . However, these earlier findings did not differentiate the effects on the plasma glucose response to an oral glucose challenge of age per se from those due to the impact of a number of age-related variables. In this context, the article by Imbeault et al. in this issue of Diabetes Care provides additional information concerning the effect of body fat on glucose tolerance, as apparently healthy volunteers grow older. However, the potential effect of differences in fitness, an age-related variable of comparable magnitude, was apparently not considered in their study.
Maneatis et al. quantified the impact of differences in age-related variables on the plasma glucose response to a mixed meal in healthy volunteers between the ages of 47 and 90 living in a retirement community. When adjusted for differences in body weight and physical activity, they found no significant correlation between age and plasma glucose response in men, and differences in age could account for no more than 6% of the variability in glucose response in women. Similarly, when adjusted for differences in weight, physical activity, and use of diabetogenic drugs, age only accounted for 6% of the variance in plasma glucose response to an oral glucose challenge in men and 1% in women in a study of 732 Italian factory workers aged 22–73 years . Perhaps the most definitive information in this regard is the results of the Baltimore Longitudinal Study of Aging , performed in 743 healthy individuals, comparing glucose tolerance in three age groups: 17–39, 40–59, and 60–92 years. When differences in overall and regional obesity as well as fitness (assessed by both history and maximal aerobic capacity) were taken into account, Shimokata et al. could find no effect of age on plasma glucose responses to oral glucose in the 17–39 and 40–59 age groups. Furthermore, partial correlation coefficients, adjusted for differences in adiposity and fitness level.