Effects of contraceptives on mother's serum and milk zinc

Abstract

The changes in concentration of zinc in serum and milk were studied in 81 nursing mothers following different contraceptive practices. Blood and milk samples from users of combined pills (levonorgestrel 0.15 mg + ethinylestradiol 0.03 mg: levorgestrel 0.25 mg + ethinylestradiol 0.05 mg; n = 15), minipill (norethindrone 0.35 mg; n = 29); injectable progesterone (depot medroxiprogesterone acetate 150 mg; n = 13), intrauterine devices (IUD) (plastic or copper; n = 5), or no contraceptives (barrier and natural methods or sterilization; n = 22) were collected before and 20 (range, 7–103) days after initiation of study. Mean length of lactation prior to taking contraceptives were 88, 73, 36, 57, and 108 days, respectively, with follow-up observation for 26, 20, 20. 18, and 22 days, respectively. Mean concentrations of serum zinc before contraceptives ranged from 0.34 to 1.14 μg/mL and no significant differences (paired t test) existed within groups after use of contraceptives, except for IUD ( P = 0.01). The normal decrease in milk zinc observed during lactation was not affected by contraceptive practices. Covariate analysis showed the concentration of zinc in samples of milk before contraceptives is a significant ( P = 0.0001) and stronger determinat of milk zinc concentration in subsequent samples than contraceptive practices. There was no significant correlation between concentrations of zinc in serum and milk ( r = −0.134, P = 0.10).