Calcium and phosphorus in milk of Brazilian mothers using oral contraceptives

J Am Coll Nutr. 1998 Dec;17(6):642-6. doi: 10.1080/07315724.1998.10718815.


Objective: Oral contraceptives (OC) are the most efficient method of contraception and it is the most prescribed by doctors in developing countries. Therefore we studied the effects of combination pill and mini-pill on calcium and phosphorus in milk of breast-feeding mothers at different stages of lactation.

Methods: Fifty-four breast-feeding mothers made up three study groups: 33 mothers who had been advised by their doctors to use either combination pill (12), or mini-pill (21), as well as a control group of 21 mothers that used no hormonal contraceptives. All mothers completed a questionnaire and provided samples of milk before and after a measured period of observation. Mean duration of study was 76, 120, and 101 days, respectively for users of mini-pill, combination pill, and controls. Determination of calcium and phosphorus was done by inductively coupled plasma-atomic absorption spectrometry.

Results: Overall the decrease in milk concentrations of phosphorus (6%) and calcium (26.3%) during the study period was not influenced by OC treatment. Regression analyses which took into consideration length of treatment, socioeconomic status, number of children, duration of previous lactation, type of contraceptive, and age of mothers and repeated measurements (before and after OC) showed that milk calcium was significantly affected by stage of lactation (p=0.0013).

Conclusion: The use of hormonal contraceptive such as the combination pill (levonorgestrel 0.15 mg+ethynilestradiol 0.03 mg) and mini-pill (norethindone 0.35 mg) does not seem to affect the secretion of calcium and phosphorus in milk of mothers.

PIP: This article is based on a study of the effects of oral contraceptives (OCs) on the concentration of calcium and phosphorus in breast milk among 54 lactating Brazilian women. Confounding constitutional variables were considered which include maternal age, previous lactation, length of breast-feeding, and variables associated with contraception, such as type and length of use. The subjects were divided into 3 groups: 12 using combination pills, 21 using mini-pills, and a control group of 21 mothers that used no hormonal contraceptives. Milk was sampled before and after a measured period of observation. The mean durations of study were 76, 120, and 101 days, respectively, for users of mini-pills, combination pills, and controls. The determination of calcium and phosphorous was done by inductively coupled plasma-atomic absorption spectrometry. The results indicate that a mean stage of lactation at start of treatment for the 3 groups ranged from 2.5 to 4 months. Both calcium and phosphorous declined in concentration with time, confounded with OC treatment. There was no significant difference for calcium concentration due to OC treatment, only stage of lactation, per se, was a significant source of variation for calcium concentration. As lactation progressed, the calcium and phosphorous concentration decreased for all mothers. Therefore, short-term use of OCs containing estrogen do not affect calcium and phosphorous concentrations in breast milk.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Adult
  • Calcium / analysis*
  • Contraceptives, Oral / adverse effects*
  • Contraceptives, Oral, Combined / adverse effects
  • Ethinyl Estradiol / administration & dosage
  • Ethinyl Estradiol / adverse effects
  • Female
  • Humans
  • Lactation*
  • Levonorgestrel / administration & dosage
  • Levonorgestrel / adverse effects
  • Milk, Human / chemistry*
  • Norethindrone / administration & dosage
  • Norethindrone / adverse effects
  • Phosphorus / analysis*
  • Regression Analysis


  • Contraceptives, Oral
  • Contraceptives, Oral, Combined
  • Phosphorus
  • Ethinyl Estradiol
  • Levonorgestrel
  • Calcium
  • Norethindrone