Oral contraceptives and intravenous glucose tolerance. II. Long-term effect.

Abstract

In order to study the long-term effect of oral contraception on glucose tolerance 40 women receiving Enovid (.5 mg norethynodrel .075 mg mestranol) were given an intravenous glucose tolerance test before 2-3 months after and 4-6 months after the initiation of contraceptive therapy. A significant (p<.001) decline in k the measure of glucose tolerance was observed after 4-6 months when compared with pretreatment values. A control group of 7 women using IUDs failed to show a similar decline. The effect of the oral contraceptive appeared early in treatment but decreased with time as two-thirds of the decline in tolerance developed in the first 9 weeks and one-third in the next 15 weeks of therapy. Diabetes suspects showed an earlier decrease in tolerance than did nondiabetic patients but their mean k remained stable after the third month of treatment. The over all tapering in the loss of glucose tolerance was followed by an improvement in 10 subjects observed for 18 months with 5 tests. This tendency may represent a loss of diabetogenicity of the progestin-estrogen mixture possibly due to compensation by greater pancreatic stimulation. No subject developed an elevated fasting blood sugar or overt diabetes. Although several abnormally low k values were recorded this pattern of change was not consistent. Evidence is insufficient to warrant indiscriminate avoidance of oral contraceptives but it is recommended that at least in diabetes suspects repeated observations of glucose tolerance be carried out during therapy.