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Journal of the American College of Nutrition, Vol. 17, No. 6, 642-646 (1998)
Published by the American College of Nutrition

Calcium and Phosphorus in Milk of Brazilian Mothers Using Oral Contraceptives

Jose G. Dorea, PhD, FACN and Edina Myazaki, PhD

Departamento de Nutrição e Departamento de Estatistica, Universidade de Brasilia, Brasilia DF, BRAZIL

Address reprint requests to: Jose Dorea, PhD, FACN, C. P. 04322, Universidade de Brasilia, 70919-970 Brasilia DF, BRAZIL


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
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.

Key words: human milk, lactation, calcium, phosphorus, hormonal contraceptives


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Changes in the quantity and composition of mother’s milk during the period of fast growth for exclusively breast-fed infants is of concern to health professionals. The nutritional benefits of exclusive breast feeding for growth, protection and well being of infants are well recognized, especially for low income classes in less developed societies. In these societies high birth rate is both a threat to the well being of mothers and an economic burden for the social development. Birth control and exclusive breast feeding must be in balance to guarantee the survival and social improvement of low income groups.

The concentrations of calcium (Ca) and phosphorus (P) in human milk varies between communities and between individuals [1]. During extended lactation a decrease in milk calcium concentration is observed as lactation progresses [2–4] although phosphorus concentrations may vary in some mothers, while maintaining stable in others [5].

During human lactation, a higher demand for Ca and P secretion in milk alters the metabolism of these elements. Due to an increase in bone turnover [6] serum Ca and P are elevated [7,8] and less urinary Ca is excreted [9]. Besides being the more efficient, oral contraceptives (OC) are the most widely used method of contraception. Even during breast feeding, the estrogen-progestin combination pill is widely prescribed (63%) by doctors in developing countries and it is estimated that 10% of breast feeding mothers around the world use OC [10].

The inhibitory effect of estrogen on bone resorption has been known and used for treatment of osteoporosis [11]. Women taking OC had higher mean bone density [12] and less urinary calcium [9] than nonusers.

The nutritional consequences of contraceptive practices on the nursing human are still unsettled. The longterm use of OC before pregnancy does not affect calcium and phosphorus concentrations in human milk [13]. A review of early publications of OC use during lactation [14], showed a decrease in milk calcium concentrations associated with combination pills. However, hormonal treatment based on progestins, such as mini-pills or implants do not show consistent results. Some studies [15,16] showed a decrease on calcium concentration while other [17] showed no significant effects. Only Toddywalla et al [16] showed an observable effect of hormonal treatment on milk phosphorus concentration. This paper aims to study the effects of OC use during lactation on the concentration of calcium and phosphorus in milk, taking into consideration confounding constitutional variables such as maternal age, previous lactation, length of breast feeding, and variables associated with contraception, such as type and length of use of OC.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 REFERENCES
 
Breast feeding mothers were recruited from private and public clinics after explaining the objectives and obtaining their consent. The mothers from private clinics were from middle class whereas the ones from public hospitals were usually slum dwellers mainly from the squatter village of Paranoa, city of Brasilia (Table 1).


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  		Table 1. Background Information on Characteristics of Mothers and Contraceptives

 
Records of variables such as stage of lactation (age of child), initiation and length of study were registered for adjusting the statistical model of analysis. The choice of contraception was decided between the mothers and their physician. Because we had no interference on choice of contraceptive or time of its initiation, we kept records of these variables for statistical adjustments and corrections.

Milk was sampled before and during treatment, at a planned interval of at least 2 weeks, between 7:00 and 11:30 a.m. The milk samples (2 to 10 mL) were collected by manual expression. Preventive measures to avoid contamination were ensured by cleaning the nipples with distilled and deionized water, and by using properly cleaned glassware (washed in acid and rinsing with EDTA solution followed by distilled and deionized water). After collection, samples were divided in aliquots and stored at -20°C until analysis.

Before analysis samples were thawed and thoroughly homogenized in a vortex. An aliquot of 2 mL of milk was accurately weighed to the nearest decimal point with an analytical scale, and mixed with 7 mL of HNO3 (Suprapur, Merck, Darmstadt, Germany). The mixture was heated at 110°C until it reached a volume of approximately 1 mL. After cooling, 2 mL of concentrated HClO4 (Suprapur, Merck, Darmstadt, Germany) were added to the digests and again heated until the liquid turned a dark brown color. The digests were cooled and 2 mL of H2O2 (30%) (Suprapur, Merck, Darmstadt, Germany) were added. The mixture was heated to 70°C until the digests turned clear and had a volume of approximately 1 mL. After cooling, the digests were quantitatively transferred to a calibrated test tube and brought to a volume of 10 mL with double distilled and deionized water.

The determination of calcium and phosphorous was done in a Inductively Coupled Plasma (ICP) Spectroflame model FVM03 with a focal distance of 75 cm (Kleve, Germany) in the emission line of 317.93 and 214.91 nm, respectively. A concentric Meihard (Kleve, Germany) nebulizer was operating under the following conditions: pressure, 38 psi; flux of cooling gas, 13 L/minute; flux of auxiliary gas, 0.5 L/minute; sample injector flow, 1 mL/minute, and forward power of 1.1 kW.

Standard Reference Material 1577 Bovine Liver (National Institute of Standards and Technology, Washington, DC) was used for quality assurance using an identical procedure on a 0.25 g of sample. All samples were processed in duplicate and the final value was taken as the mean of running each sample three times against standards prepared from solutions for atomic absorption spectroscopy (Merck, Darmstadt, Germany).

The effects of contraceptives on changes in concentrations of calcium and phosphorus in milk were studied by a multiple regression analysis taking into account, age of mother, number of children, socioeconomic status, day of lactation on first day of treatment, length of treatment, and type of contraceptive [18].

The data were summarized as means±SD and ranges. Statistical computations were done with a SAS computer program for PC (SAS Institute, Cary, NC). A p value less than 0.05 was considered statistically significant.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 REFERENCES
 
The characteristics of mothers and lactation information as well as type of contraceptives are shown in Table 1. Although some mothers had started taking oral contraceptives as early as 2 weeks post-partum others started treatment after the third month. Mean stage of lactation at start of treatment for the three groups ranged from 2.5 to 4 months. We had scheduled the second sample (post-treatment) to take place at least 2 weeks after initiation of treatment. Certain difficulties, in particular with the mothers in keeping appointments, caused the variation in length of treatment between mothers. These sources of variability were accounted for in the regression analysis.

Table 2 shows the summary of concentration of milk calcium and phosphorus as a function of contraceptive type. For both minerals there was a decline in concentration with time that is confounded with OC treatment. The statistical analysis is shown in Table 3. Overall no significant difference was seen for calcium concentration due to OC treatment, only stage of lactation per se was a significant source of variation for calcium concentration.


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  		Table 2. Summary of Results as Mean and (SD) of Concentrations (µg/g) of Calcium and Phosphorus in Milk of Mothers Using Oral Contraceptives

 

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  		Table 3. Summary of results (p) of statistics of multiple regression analysis

 
The distribution of calcium and phosphorus concentrations in milk as a function of length of lactation for all mothers in Fig. 1, shows a decline in calcium concentration as lactation progresses. For comparative purposes Table 4 shows summary of studies dealing with hormonal contraceptive effects on milk concentrations of calcium and phosphorus.



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  		Concentrations of calcium and phosphorus in milk according to length of lactation.

 

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  		Table 4. Summary of Results of Studies Relating Hormonal Contraceptive Effects During Lactation on Milk Concentration of Calcium and Phosphorus and Respective Statistical Analysis of Data

 

   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
REFERENCES
 
Results of our study are in good agreement with world wide reports on calcium and phosphorus concentrations [19]. A review of the calcium concentration in milk before 1978 was made by Jelliffe and Jelliffe [20] which shows results from Brazil (204 µg/g), Bantu, Africa (208 to 287 µg/g), UK (299 µg/g), New Hibrides (258 µg/g), US (340 µg/g), India (342 µg/g), and Australia (286 to 307 µg/g). In all these studies, range of variations are comparable between affluent and developing countries. As observed previously [2–4], we confirm the decline in calcium due to progress of lactation.

The calcium demand of lactation is met by the favorable hormonal balance in postpartum, where women are hyperprolactemic and hypoestrogenic. Under such circumstances calcium and phosphorus depots are easily mobilized by PTH. Later in lactation with resumption of menses and elevation of estrogen, markers of bone mobilization are lowered [21]. It has been shown that milk production is diminished by combined oral contraceptives [22] but it is not affected by progestins [23].

In spite of reports that the hormonal contraception can affect lactation [14], both quantitatively (milk yield), as well as qualitatively (specific nutrients such as calcium and phosphorus), we could not confirm the decrease in calcium seen for long-term use of high estrogen dose of combination pills [15–17] and progestins [15–16]. Our results however, agreed with the study of Toddywalla et al [16] with regards to the effect of low dose estrogen-pill on milk calcium concentration. The consistent decrease in milk calcium observed by others (Table 4) in association with combination pill could be explained by the elevated doses of estrogen used in those studies. Comparatively, the dose of estrogen (0.01 mg of ethinylestradiol) studied by Toddywalla et al [16] was smaller than others (0.05 to 0.1 mg of estrogen) and similar to our study. Other differences in studies were the length of hormonal treatment, and statistical analysis employed. The shorter hormonal treatment and the smaller dose in our study could explain in part why we found no significant effect on calcium due to estrogen treatment.

It is noteworthy that statistical analysis used by early investigators did not fully account for important intervening variables. A summary of statistical shortcomings is shown in Table 4. In most studies where statistical methods were described the effect of contraceptives was measured within each group as differences in absolute or relative changes in mineral concentrations over 1 to 10 month periods. Indeed, control groups used and analyzed independently, also showed significant decreases in milk components associated with stage of lactation [15,24].

The statistics of simple mean comparison within each group may be adequate when there are no other intervening variables. In the case of nutrient composition of human milk, specially calcium and phosphorus it has been suggested that diet, ethnicity and behavior [25,26] may affect the incorporation of these elements into breast milk. Besides, the type of contraceptive chosen by the women was of a different composition with different concentrations of estrogens and progestins. These hormones known to either affect lactation [14] or calcium metabolism (estrogens) in particular, could have a cumulative effect that needed evaluation in combination with other variables. Since none of the studies employed a statistical model which could handle analysis that included intervening variables, mainly time dependent decrease in milk calcium or rates of changes in concentrations of the minerals during the OC treatment, their findings could be questioned.

Statistical selection of limited capability or lack of proper description has reduced the general applicability of findings in some of the papers summarized in Table 4. Worst of all, some of the papers that presented results claiming an effect of OC on calcium and phosphorus lacked valid statistical conclusions. If definite conclusions are to be drawn regarding OC effects on milk concentrations of nutrients, future research must avoid the errors of the past. In the present study, a multivariate statistical method of analysis, did not show that short term use of OC-containing estrogen affected calcium and phosphorus concentrations in milk.


   ACKNOWLEDGMENTS
 
This work was supported in part by a grant from the Brazilian National Research Council (CNPq). We thank the mothers that contributed to the study and the interest and cooperation of Drs. Lucila Mota, Iraci Oliveira, and H. Borato, and nurses Sonia Silveira and Celina Santana from University of Brasilia Hospital, and Posto de Saude 15-FHDF. We also thank Dr. Teresa Costa for collection of samples and Dr. Geraldo Boaventura and Paulo Roque Silva for laboratory work, as well as Dr. Connie McManus for redactorial suggestions.

Received September 1, 1997. Accepted May 1, 1998.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 

  1. Prentice A, Dibba B, Jarjur LMA, Larskey MA, Paul AA: Is breast milk calcium concentration influenced by calcium intake during pregnancy? Lancet 344: 422–412, 1994.
  2. Finnley DA, Lonnerdal B, Dewey KG, Grivetti LE: Inorganic constituents of breast milk from vegetarian and non vegetarian women: Relationships with each other and with organic constituents. J Nutr 115: 772–781, 1985.
  3. Allen JC, Keller RP, Archer P, Neville MC: Studies in human lactation: milk composition and daily secretion rates of macronutrients in the first year of lactation. Am J Clin Nutr 54: 69–80, 1991.[Abstract/Free Full Text]
  4. Neville MC, Allen JC, Archer PC, Casey CE, Seacat J, Keller RP, Lutes V, Rasbach J, Neifert M: Studies in human lactation: milk volume and nutrient composition during weaning and lactogenesis. Am J Clin Nutr 54: 81–92, 1991.[Abstract/Free Full Text]
  5. Laskey MA, Dibba B, Prentice A: Low ratios of calcium to phosphorus in breast milk of rural Gambian mothers. Acta Paediatr Scand 80: 250–251, 1991.[Medline]
  6. Sowers M, Randolph J, Shapiro B, Jannausch M: A prospective study of bone density after pregnancy. Obstet Gynecol 85: 285–289, 1995.[Abstract]
  7. Specker BL, Tsang RC, Ho ML: Changes in calcium homeostasis over the first year postpartum: effect of lactation and weaning. Obstet Gynecol. 78: 56–62, 1991.[Abstract/Free Full Text]
  8. Kalkwarf HJ, Specker BL, Heubi JE, Vieira NE, Yergey AL: Intestinal calcium absorption of women during lactation and after weaning. Am J Clin Nutr 63: 526–531, 1996.[Abstract/Free Full Text]
  9. Klein CJ, Moser-Villon PB, Dopuglass LW, Ruben KA, Troeki O: A longitudinal study of urinary calcium, magnesium and zinc excretion in lactating and non-lactating postpartum women. Am J Clin Nutr 61: 779–786, 1995.[Abstract/Free Full Text]
  10. Strauss LT, Speckhard M, Rochat RW, Senanayake P: Oral contraceptive during lactation: A global survey of physician practice. Int J Gynaecol Obstet 19: 169–175, 1981.[Medline]
  11. Kitai E, Blum M, Kaplan B: The bone sparing effect of oral contraceptive use in non-smoking women. Clin Exp Obstet Gynecol. 19: 30–33, 1992.[Medline]
  12. Wolman RL, Clark P, McNally E, Harries MG, Reeve J: Dietary calcium as a statistical determinant of spinal trabecular bone density in amenorrhoeic and oestrogen-replete athletes. Bone Miner Res 17: 415–423, 1992.
  13. Kirksey A, Ernst JA, Roepke JL, Tsai TL: Influence of mineral intake and use of oral contraceoptive on the mineral content of human colostrum and more mature human milk. Am J Clin Nutr 32: 30–39, 1979.[Free Full Text]
  14. Hull VJ: Research on the effects of hormonal contraceptives on lactation: Current findings, methodological considerations and future priorities. Wld Hlth Quart 36: 168–200, 1983.
  15. Abdel-Kader MMA, Hay AA, El-Safouri S, Aziz MTA, el-Safouri S, Saad el-Din J, Kamal I, Hefnawi F, Abdalla M: Clinical, biochemical and experimental studies on lactation. IV. Quantitative and qualitative changes induced in goat’s milk by gestagens. Am J Obstet & Gynecol 105: 978–985, 1969.[Medline]
  16. Toddywalla VS, Joshi L, Virkar K: Effect of contraceptive steroid on human lactation. Am J Obstet Gynecol 127: 245–249, 1977.[Medline]
  17. Barsivala VM, Virkar KD: The effect of oral contraceptives on concentrations of various components of human milk. Contraception 7: 307–312, 1973.
  18. Diggle PJ, Liang K-Y, Zeger SL: "Analysis of Longitudinal Data." Oxford, UK: Oxford Science Publications, pp 55–77, 1996.
  19. Parr RM, Demayer EM, Iyengar VG, Byrne AR, Kirkbright GF, Schoch G, Niinisto L, Pineda O, Vis HL, Hofvander Y: Minor and trace elements in human milk from Guatemala, Hungary, Nigeria, Philippines, Sweden and Zaire. Results from a WHO/IAEA Joint Project. Biol Trace Elem Res 29: 51–75, 1991.[Medline]
  20. Jellife D, Jelliffe EFP: The volume and composition of human milk in a poorly nourished communities. A review. Am J Clin Nutr 31: 492–515, 1978.[Free Full Text]
  21. Zinaman MJ, Hickey M, Tomai TP, Albertson BD, Simon JA: Calcium metabolism in postpartum lactation: the effect of estrogen status. Fertil Steril 54(3): 465–469, 1990.[Medline]
  22. Saarikoski M: Contraception during lactation. Ann Med 25: 181–184, 1993.[Medline]
  23. McCann MF, Moggia AV, Higgins JE, Potts M, Becker C: The effects of a progestin-only contraceptive (levonorgestrel 0.03 mg) on breast-feeding. Contraception 40: 635–648, 1989.[Medline]
  24. Seth U, Yadava HS, Agarwal N, Laumas KR, Hingorani V: Effect of sub dermal silastic implant containing norethindrone acetate on human lactation. Contraception 16: 383–398, 1977.[Medline]
  25. Hillman LS: Mineral and vitamin D adequacy in infants fed human milk or formula between 6 and 12 months of age. J Pediatr 117: S134–S142, 1990.[Medline]
  26. Prentice A, Barclay DV: Breast-milk calcium and phosphorus concentrations of mothers in rural Zaire. Eur J Clin Nutr 45: 611–617, 1991.[Medline]




This Article
Right arrow Abstract Freely available
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Right arrow Articles by Dorea, J. G.
Right arrow Articles by Myazaki, E.

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