Effects of oral contraceptives on carbohydrate metabolism

Abstract

Both estrogens and progestogens modify carbohydrate metabolism, and their ultimate effect depends upon the ratio of one to the other. The effect of progestogens themselves, which are responsible for increased insulin secretion and for insulin resistance, varies according to their androgenicity but increases according to the series pregnane, estrane and gonane. In contrast, estrogens impair the initial secretion of insulin by the pancreas. The prolonged use of combined oral contraceptives containing the powerful progestogen levonorgestrel is associated with mild but continuing glucose intolerance and with marked insulin resistance.

PIP: Investigations into the effects of combination oral contraceptives (OCs) on carbohydrate metabolism indicate that these effects depend on the dose of estrogen and the dose and type of progestogen. The effect of progestogens, which are responsible for increased insulin secretion and for insulin resistance, varies according to their androgenicity but increases according to the series pregnane, estrane, and gonane. In contrast, estrogens impair the initial secretion of insulin by the pancreas. Long term use of levonorgestrel-containing OCs is associated with mild but continuing glucose intolerance and with marked insulin resistance. Data from a cross-sectional study of the effects of OCs on carbohydrate metabolism indicated a progressive decrease over time in the ratio of incremental insulin area to incremental glucose in women taking an OC containing 30 mcg of ethinyl estradiol and 150 mcg of levonorgestrel. In an identical study of women using an OC containing 20 mcg of estrogen and 1 mg of norethindrone acetate, there was a moderate deterioration in glucose tolerance at 3 months but no change after this point and a moderate increase in insulin secretion that also remained constant after 3 months. Given growing evidence that elevated glucose and insulin levels a independent risk factors in cardiovascular disease, it is suggested that OC formulations causing the least insulin resistance (ie 30-35 mcg of estrogen and 1 mg of norethisterone acetate) should be used.