National Osteoporosis Awareness and Prevention Month
LAM and Neuroendocrine Effects on Fertility and Bone: A Review
By: Magdalene Lederer
Director’s Note: Since May is also National Osteoporosis Awareness and Prevention Month, this week we feature a 2022 review by Calik-Ksepka et al [1] published in the International Journal of Molecular Sciences titled, “Lactational Amenorrhea: Neuroendocrine Pathways Controlling Fertility and Bone Turnover.” The review article, summarized by former FACTS elective participant Magdalene Lederer, addresses the link between breastfeeding and bone turnover. Not only is breastfeeding relevant for the family planning applications of the lactational amenorrhea method, but this article also explores the influence of lactation on neuroendocrine pathways with widespread effects in the body.
Breastfeeding Physiology
The article by Calik-Ksepka et al [1] reviewed the available research on the physiology of both the lactational amenorrhea method (LAM) and the bone turnover that occurs during breastfeeding. Before understanding how lactation can induce amenorrhea, it is important to explain the physiology behind lactation. To prepare for lactation, breasts require a change and development within the glandular tissue. This process relies on estrogen, progesterone, and prolactin, and their changes in prevalence during pregnancy and postpartum.
“To prepare for lactation, breasts require a change and development within the glandular tissue. This process relies on estrogen, progesterone, and prolactin.”
Estrogen plays two roles: it promotes physical changes in the breast, including ductal development, and stimulates prolactin secretion. During pregnancy, however, estrogen is unable to promote significant prolactin secretion because the high progesterone levels inhibit this effect until after delivery of the placenta. This is one reason for the different types of milk seen at the end of pregnancy through day one, typically referred to as colostrum, transitional milk from days 2-5, and mature milk produced from day 5. When suckling occurs, mechanoreceptors at the breast trigger oxytocin release, which stimulates the let-down reflex that mediates breastfeeding. Oxytocin increases contraction within the breast to allow milk to flow toward the nipple and also stimulates prolactin release, which leads to a positive feedback loop: continued breastfeeding empties the breast, further increasing prolactin release as well as the milk supply.
Lactational Amenorrhea
The neurochemical control of lactational amenorrhea has not been fully researched. It is clear that the female hypothalamus-pituitary-ovarian (HPO) axis is affected by both pregnancy and breastfeeding. During pregnancy, placental hormones inhibit the HPO axis. After pregnancy, breastfeeding can maintain amenorrhea. Studies reveal that follicle stimulating hormone (FSH) returns to levels similar to that of the follicular phase by 4 weeks postpartum. Luteinizing hormone (LH) has also been demonstrated to return to low normal levels by 4 weeks postpartum. With both hormones needed for menstruation present, it seems another mechanism is at play.
In a menstruating woman, LH is released in pulses. Breastfeeding and suckling in particular disrupt this pulsatile nature of LH secretion, which results in anovulation. The LH release corresponds with gonadotropin-releasing hormone (GnRH) release. Kisspeptin is a stimulator of GnRH. Although research has only been conducted in rats, suppression of kisspeptin may be the main suppressor of GnRH, which in turn would suppress LH pulsatile release. The exact mechanism of this phenomenon needs more research to identify differences in moms who exclusively breastfeed, moms who breastfeed and pump, and moms who exclusively pump.
“Breastfeeding and suckling in particular disrupt this pulsatile nature of LH secretion, which results in anovulation.”
Lactational Amenorrhea Method
Studies demonstrate LAM can be 98% effective when used alone under these conditions:
- up to 6 months from delivery,
- exclusive or nearly exclusive breastfeeding, and
- no return of menses.
If any one of these conditions is no longer met, another method should be used for family planning. Exclusive or nearly exclusive breastfeeding is an important aspect of the success of this method. Any food or liquids given could delay the frequency and/or duration of infant suckling and thus affect HPO axis suppression, which could lead to ovulation. Initial return of menses is most likely anovulatory, but once it has returned, the possibility of ovulation increases significantly.
Lactation and Bone Turnover
Lactation does more than affect the menstrual cycle; it can also lead to bone turnover. Estrogen is lower during lactation, leading to bone remodeling. Yet, estrogen rises upon discontinuation of breastfeeding, and bone formation occurs. In patients with pre-existing risk factors for osteoporosis, pregnancy-and-lactation-induced osteoporosis can occur and can lead to fractures. While the extent of bone loss varies among breastfeeding women, there is a consistent change when compared to mothers who choose formula rather than breastfeed. The greatest bone losses tend to be in the lumbar spine. Once lactation ends, however, these changes typically reverse and mineral content within the skeleton is restored to baseline.
“Estrogen is lower during lactation, leading to bone remodeling. Yet, estrogen rises upon discontinuation of breastfeeding, and bone formation occurs.”
Summary
In conclusion, breastfeeding has many effects on the lactating mother. Amenorrhea is a significant physiological change that deserves more attention in research. Bone turnover for the calcium in breastmilk is significant during the breastfeeding period but resolves quickly once lactation ends. This article demonstrated the significant gaps in research connecting lactation and the menstrual cycle. Potential differences between breastfeeding and pumping at the neurochemical level also need to be explored. Such differences would impact the usefulness of LAM for women who are unable to breastfeed without pumping, particularly in the U.S. where there is no guaranteed maternity leave and many women return to work well before their newborn is 6 months old.
Despite conflicting data regarding bone turnover and its mechanism, consistent evidence shows bone turnover during breastfeeding is temporary, and women return to baseline after lactation ends. On the other hand, women with preexisting risk factors for osteoporosis may need more calcium support to prevent fractures.
This article [1] provides insight into information and data to investigate further about female physiology. It also reinforces the value of exclusive breastfeeding for the first 6 months postpartum, which needs to be recognized at both the individual and societal level to maximize its benefits.
References
[1] Calik-Ksepka A, Stradczuk M, Czarnecka K, Grymowicz M, Smolarczyk R. Lactational Amenorrhea: Neuroendocrine Pathways Controlling Fertility and Bone Turnover. Int J Mol Sci. 2022 Jan 31;23(3):1633. doi: 10.3390/ijms23031633. PMID: 35163554; PMCID: PMC8835773.
ABOUT THE AUTHOR
Magdalene Lederer
Magdalene Lederer is a fourth-year medical student at Rowan-Virtua School of Osteopathic Medicine in Stratford, NJ. She completed her undergraduate education at Liberty University in Lynchburg, VA and will begin residency in obstetrics and gynecology this summer at Saint Peter’s University in New Brunswick, NJ. She is excited to provide informed consent to her patients about family planning options, from contraception to infertility.
