Insulin Sensitivity Is Decreased in Normal Women by Doses of Ethinyl Estradiol Used in Oral Contraceptives

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Abstract

OBJECTIVE

We determined the independent effects of various doses of ethinyl estradiol used in oral contraceptives or norethindrone acetate, as well as their combination, on insulin sensitivity in normal women.

STUDY DESIGN

Thirty-three normal ovulatory female volunteers were recruited for this study. Insulin tolerance tests were performed after carbohydrate loading to determine the kinetic disappearance of glucose and insulin. After initial testing the women were randomized into four groups: ethinyl estradiol 20 micrograms, 35 micrograms, and 50 micrograms and norethindrone 1 mg. Insulin tolerance tests were repeated after 1 month of treatment and again after a second month, when all ethinyl estradiol groups received the addition of norethindrone 1 mg to their doses of ethinyl estradiol. Plasma glucose and insulin were measured, and insulin sensitivity (Kitt glucose) and the disappearance of insulin (Kitt insulin) were calculated.

RESULTS

All groups were comparable at baseline, and no significant changes in fasting glucose and insulin were evident with treatment. After ingestion of 50 micrograms ethinyl estradiol the Kitt glucose value decreased significantly (p < 0.03) and ingestion of 20 micrograms and 35 micrograms showed individual changes, but as groups the changes were not statistically significant. All ethinyl estradiol groups combined had a significant decrease in Kitt glucose (p < 0.01). Norethindrone 1 mg alone did not change Kitt glucose values, and after the addition of norethindrone to ethinyl estradiol, Kitt glucose values normalized. K sub itt insulin values were also lower with treatment but were lower with ethinyl estradiol plus norethindrone compared with ethinyl estradiol alone (p < 0.04), suggesting an attenuation of insulin clearance with the progestin.

CONCLUSION

Ethinyl estradiol alone decreases insulin sensitivity, and this may occur at lower doses, but norethindrone 1 mg does not appear to do so. However, progestins may alter insulin clearance. (AM J OBSTET GYNECOL 1993;169:1540-4.)

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