Influence of the menstrual cycle on glucose tolerance and insulin secretion.

To evaluate the impact of the menstrual cycle on glucose tolerance and insulin secretion, in the present study we have measured the plasma concentrations of glucose, insulin, and C-peptide during a 2-hour oral glucose tolerance test in 110 healthy, nonobese, regularly menstruating women. Fifty-five women were in the follicular phase, and 55 were in the luteal phase of the cycle. The two groups were well matched for age and body weight. Plasma concentrations of glucose, insulin, and C-peptide either in the fasting state or after the oral glucose load did not differ in the two groups. These results suggest that in nondiabetic women the menstrual cycle has no major effect on glucose tolerance and insulin secretion and that the phase of the menstrual cycle should not be considered in programming and interpreting an oral glucose tolerance test.