Pregnancy and lactation represent phases of intense female bodily changes, requiring an increased demand for calcium. This mineral is necessary both to support the skeletal development of the fetus and for the production of breast milk that nourishes the newborn in the first months or years of life.
If the mother does not have enough calcium, the body extracts it directly from its own skeleton, which can cause bone mass loss ranging from 3% to 10% during the first four months of exclusive breastfeeding. However, this loss tends to be reversed when the baby's diet is supplemented after six months of exclusive breastfeeding, at which point hormonal levels normalize and menstruation returns.
Considering the risk that bone fragility poses to women's future health and quality of life, Professor Tamara Beres Lederer Goldberg, along with two doctoral students from the Postgraduate Program in Tocogynaecology at the Faculty of Medicine of Unesp in Botucatu, initiated a study. The objective was to verify whether the volume of milk produced influenced bone mass loss, comparing mothers who only breastfed their children with those who also donated milk to human milk banks.
The study's coordinating professor initially expected that producing a larger volume of milk would lead to greater bone deterioration, but the results indicated the opposite: 'The impact is the same.' These findings were published in the Journal of Pediatrics.
Between July 2020 and March 2023, the research monitored 77 nursing mothers. Of these, 38 fed only their babies, while 39 donated excess breast milk during the period. The first group was evaluated 15 days and six months after birth, and the second group was evaluated at six and twelve months postpartum.
To minimize the influence of external variables on bone mass, women aged between 18 and 38 were selected, who were pregnant for the first time, with pregnancy classified as low risk, and whose babies were born full-term and with adequate weight for gestational age. Women with obesity or diseases that could affect bone metabolism were excluded from the study.
All participants were assessed for Body Mass Index (BMI) and underwent densitometry exams to measure bone mineral density in three areas: lumbar spine, total proximal femur, and whole body. Additionally, blood samples were collected to quantify calcium, phosphorus, vitamin D, estradiol, parathyroid hormone, and markers of bone formation and resorption. The volume of milk donated by each participant was also recorded.
After six months of breastfeeding, the bone mass test results of the two groups were identical. Tamara emphasized that there was no previous literature investigating the effects of breast milk donation on the bone health of donors. She mentioned that the initial reasoning was that donating large volumes of milk, in addition to personal consumption, should negatively impact bone mass, but this did not occur, which was a surprising finding.
Between six and twelve months after birth, when breastfeeding was already supplemented, the bone mineral density values of the lumbar spine and femur in milk donors showed increases of 5% and 1.5%, respectively, signaling the beginning of a regeneration process by the body. No significant changes in BMI were noted.
Regarding biomarkers, the trend of bone recovery was confirmed by the observed changes. The most relevant finding was the decrease in CTX starting from the sixth month of breastfeeding. This biomarker indicates the degradation of bone collagen, and its drop, along with the reduction in bone alkaline phosphatase (an indicator of bone formation), suggests a slowdown in bone remodeling activity.
When comparing the data of donors at 12 months with that of non-donors at 15 days, after necessary statistical adjustments, it was found that even while maintaining complementary breastfeeding, bone mineral density values tended to return to the averages recorded shortly after birth. Tamara concluded that although there is an 'aggression,' bone mass loss is temporary, and breast milk donation does not worsen bone health more than breastfeeding itself.
It is important to note that bone mass loss during exclusive breastfeeding, despite being transient, is more pronounced than that observed in women in menopause, who record an annual loss of 1% to 3%, constituting a factor that can affect long-term quality of life, requiring attention to bone quality before pregnancy.
The researchers also observed that the women studied had low calcium intake through diet and, during pregnancy, did not receive calcium or vitamin D supplementation, nutrients crucial for maintaining and gaining bone mass. Tamara commented that in the SUS, the offering is limited to folic acid, while women in private services receive these supplements, but without tests to assess the sufficiency of the doses. She pointed out the scarcity of research validating the ideal amounts for this period of female life.
The results of this work open new avenues for investigation. Currently, Tamara leads a study focused on bone mass loss during pregnancy, focusing on women attended in the Unified Health System in Botucatu. The purpose is to map the bone mass of pregnant women throughout the entire pregnancy to identify periods of highest risk, thus helping to guide public health policies.
The researcher also expressed interest in investigating the impact of multiple pregnancies on bone quality, the effect of maternal obesity—due to the chronic inflammatory process—, and possible differences in bone mass between white and black women. However, she reinforced that such issues do not change the recommendation regarding breastfeeding, which, according to the World Health Organization (WHO), should be exclusive until six months and supplemented until two years or more.
Tamara concluded by saying that the study serves as a warning to gynecologists and pediatricians, emphasizing that the success of breastfeeding depends on professional support and guidance, because 'breastfeeding is a social process.'