Breastfeeding and Bone Health
by Anne Eglash MD, IBCLC, FABM
Breastfeeding is known to be associated with a drop in a woman’s bone density, particularly when she is exclusively breastfeeding. This week’s article is a newly published systematic review and meta-analysis of 32 international studies done on the effect of lactation on bone density. According to the authors, the high prolactin level during lactation causes ovarian function to pause, leading to a drop in estrogen, and lack of menstruation. A low estrogen state is at least partially responsible for the bone loss during lactation, similar to what happens during menopause. In addition, a hormone made by milk-producing cells called the parathyroid hormone related protein (PTHRP) controls the calcium level in breastmilk by preferentially taking calcium from the bones, rather than from calcium ingested. This is why a breastfeeding mother cannot substantially counteract bone loss during lactation by eating more calcium rich foods.
Lactation-related bone loss is more likely to occur in the spine vs the hips. It is rare for women to develop fractures from bone loss, and if they do occur, they tend to develop in the spine in the first few weeks of lactation.
The good news is that the bone loss during lactation is considered temporary, and the overall trend in the studies in this systematic review shows that bone density recovers at some point after weaning.
- Adolescents who breastfeed are at higher risk of never achieving their full adult bone density potential.
- Women with a higher body mass index (BMI) have less bone loss during lactation.
- Women who become pregnant less than 18 months after weaning never recover their bone loss from lactation.
- Breastfeeding women don’t recover bone loss until after they wean, even if they are menstruating, because of continual loss of calcium through breastmilk.
See the Answer
Lactation has been associated with significant temporary bone loss, especially during the exclusive breastfeeding period. In the bone recovery phase, there is wide methodological heterogeneity among clinical trials, including follow-up timing, methods and sites of bone measurements, and body composition changes. The purpose of this study is to perform a systematic review and metaanalysis aiming to evaluate the recovery rate of bone mass after lactation-related loss, including the PubMed, Web of Science, and Scopus databases, with no publication date restrictions. The following MeSH terms were used: bone diseases, bone resorption, bone density, osteoporosis, calcium, postpartum period, weaning, breast feeding, and lactation. The inclusion criteria were as follows: prospective human studies in women of reproductive age and bone measurements with two assessments in the postpartum period at least: the first one within the first weeks of lactation and another one 12 months after delivery, 3 months following the return of menses or 3 months postweaning. This research was recorded on the Prospero database (CRD42018096586Bone). A total of 9455 studies were found and 32 papers met the inclusion criteria. The follow-up period ranged from one to 3.6 years postpartum. Lactation was associated with transient bone loss, with a strong tendency to recover in all the sites studied, depending on the return of menstruation and weaning. Small deficits in the microarchitecture of the peripheral skeleton may be present, especially in women with prolonged breastfeeding, but with no deficit regarding the hip geometry was found. Women with a successive gestation after prolonged lactation and women who had breastfed when adolescents had no significant bone loss. Bone loss related to lactation is transitory, and several compensatory homeostatic mechanisms are involved to minimize any significant damage to the maternal skeleton.
Six studies in this systematic review evaluated lactating adolescent mothers, and found that they had full bone density recovery and no negative impact on peak bone mass acquisition.
Some of the studies demonstrated that body mass index played a role in the amount of bone density loss during lactation, with greater BMI associated with less bone loss.
Becoming pregnant during breastfeeding or soon after weaning actually has a positive impact on bone density. Estrogen levels are higher, which is positive for bone density, and the maternal gut enhances its calcium absorption during pregnancy.
Return of menses during lactation likely helps to attenuate continued bone loss because of the higher estrogen state, but the parathyroid hormone-related protein present during lactation still has significant control over the amount of calcium taken from bones. Therefore, return of menses during lactation may help to decrease bone loss, but its effect is likely variable.