Effect of Lactation on Maternal Bone Mineral Density: Understanding the Association

Introduction:

The study of changes in bone mineral density during lactation can be challenging, as this involves various radiographic tests. The radiation hazard of these tests can harm the mother and the child. However, new studies like DEXA have been used to study bone mineral density. The radiation exposure of DEXA is less compared to other studies. The human skeletal system provides both mechanical and mineral support to the body. Depletion of this mineral content can give rise to conditions like osteopenia and osteoporosis.

What Are the Effects of Pregnancy on Bone Health?

There is a drastic change in calcium metabolism during pregnancy. The body absorbs maximum calcium from the mother’s body for the development of a growing fetus. This mineral transfer leads to low BMD during pregnancy and lactation. On average, one percent to nine percent of BMD loss occurs from conception to delivery. Following are the changes seen in BMD during pregnancy:

• Increased intestinal absorption of calcium for fetus growth.

• Increased serum lipids and triglycerides with a low BMD level lead to an increased risk of osteoporosis and cardiovascular disease.

• Long lactation periods create more BMD loss.

• Various site-specific bone loss is noted. The trabecular sites, such as the lumbar spine, hip, and distal radius, showed the highest rate of bone loss due to lactation. At the same time, the cortical sites showed less bone loss. This occurred mainly because of hormonal changes.

• When the fetal requirement of calcium exceeds the maternal supply, this creates metabolic stress in mothers.

• Increased calcium demand leads to increased fracture risk.

• A woman who gives birth to multiples showed more loss in BMD. However, the body compensates for remineralization once breastfeeding stops.

What Are the Complications Seen in Low BMD-Induced Child Delivery?

If there is a drastic depletion in the concentration of serum calcium level in the body, this can lead to the following complications:

• Musculoskeletal injury.

• Loosened ligaments.

• Pelvic health dysfunction.

• Decreased bone mineral level.

• Injury to the pelvic floor at childbirth.

• Urine incontinence.

• Fetal incontinence at childbirth.

• Pelvic prolapse.

What Are the Effects of Lactation on Bone Mineral Density (BMD)?

Around 200 to 400 milligrams of calcium are required to produce daily milk. A lot of calcium is lost from a mother’s milk during lactation by expressing the hypothalamic-pituitary-ovarian axis at lactation time. Once breastfeeding stops, the body starts releasing estrogen hormone, which helps the body to recover the lost minerals.

Summary of Pregnancy, Lactation, and Drug Effect on Bone Mineral Density and Fracture Risk:

• Pregnancy- The change in BMD decreases <1 % to 9 % with full BMD recovery. The risk of fracture is less. The number of delivery or parity gives protection against hip joint fractures, especially in postmenopausal women.

• Lactation- The change in BMD decreases by 1 % to 8 % with full BMD recovery. The risk of fracture is less. Breastfeeding helps to create a protective effect on hip fractures, especially in postmenopausal women.

• Use of DMPA (Depot Medroxyprogesterone Acetate) - The change in BMD decreases 3 % to 4 % (1 year) and decreases 6 % - 8 % (2 years) with partial to full BMD recovery. The risk of fracture is less. Breastfeeding helps to create a protective effect on hip fractures, especially in postmenopausal women.

• Use of Gonadotropin-Releasing Hormone (GnRH) Agonist- The change in BMD decreases 3 % to 4 % (1 year) and decreases 6 % to 8 % (2 years) with partial to full BMD recovery. The risk of fracture is not known.

• Use of GnRH Antagonists- The change in BMD decreases <1 % to 4 % (6 months) and Decreases 1 % to 5 % (1 year) with partial to full BMD recovery. The risk of fracture is not known.

How Does a Bone Mineral Density Vary in an Individual?

The change in BMD varies in measurement concerning different body parts. A study of BMD during lactation within the first six months of delivery demonstrated the percentage of different bone depletion and showed the following results:

• Radius Bone- 1 to 5 percent.

• Spine Bone- 2 to 3 percent.

• Femoral Neck Bone- 3 to 6 percent.

• Forearm Bone- 1 to 2 percent.

• Hip Bone- 4 percent.

• Trochanter Bone- 4 percent.

• Lumbar Spine Bone- 1 to 8 percent.

Extreme body parts like hands and feet show different mineral deposition values. The values of BMD also vary among different populations. The change in BMD is noted during and after lactation. The femoral and hip bones showed a four percent reduction in bone density during lactation and a one percent reduction in the lumbar spine.

Is There Any Risk of Fracture Associated With Pregnancy and Lactation?

The chances of fracture are low during the third and fourth decades of life, especially during pregnancy and lactation. However, the prevalence of fracture in pregnancy and during lactation is estimated to be around four to eight per one million pregnancies with lactation-associated-osteoporosis. The chances of fracture increase with age and are high during the menopausal period. The risk of fracture doubles after fifty years of age. Hence, no evidence supports the relationship between pregnancy and lactation with an increased risk of fracture.

What Other Conditions Can Lead to Low Bone Mineral Density in Women?

A woman experiences an increase in her BMD at the time of puberty. Once she hits thirty, there is a natural decrease in BMD due to aging. Other events like pregnancy and lactation also cause a decrease in BMD. The major threat for low mineral density occurs during menopause, and the chances of fracture are high. However, other conditions can also lead to BMD, such as:

• Trauma or fracture can cause osteoporosis, depending on the person's age and trauma site.

• Medical conditions like hyperparathyroidism, hyperthyroidism, and Cushing's syndrome can cause low BMD.

• Intake of medications can cause BMD. For example, contraceptives, glucocorticoids, antidiabetic medications, antiepileptics, selective serotonin reuptake inhibitors, chronic heparin, gonadotropin-releasing hormone (GnRH), and antipsychotic drugs. However, using contraceptive pills has shown a neutral effect on BMD.

• Women who take depot Medroxyprogesterone acetate (DMPA) and gonadotropin-releasing hormone (GnRH) agonists during the perimenopausal period have been associated with low BMD.

• Medical conditions like endometriosis-associated pelvic pain, heavy menstrual bleeding, and uterine fibroids have been treated using GnRH antagonists. For example, ASP1707, Elagolix, Linzagolix and Relugolix. These medicines have shown an impact on BMD.

What Are the Tests Available to Detect Bone Mineral Density?

Every woman after her menopause age is advised to do an osteoporosis screening. The woman who is on risk factors such as medications like glucocorticoids, use of an antiepileptic drug, chronic heparin aromatase inhibitor therapy, and woman who have a family history of osteoporosis, low body mass (>BMI), previous history of fracture, smoking habit, and excessive alcohol use are all suggested to undergo a BMD assessment. Tests done to monitor the BMD are as follows.

• DEXA (Dual Energy X-ray Absorptiometry): This test evaluates bone density.

• BMD T-score: -2.5 or less indicative of a high risk of fracture.

• BMD T-score: -1 to -2.5 indicates >3 % risk of hip fracture or >20 % risk for major osteoporotic fracture for about ten years.

• Quantitative Ultrasound (QUS): This is done to study the bone recovery rate post-weaning.

• High-Resolution Peripheral Quantitative Computed Tomography (HR-pQCT): This test is done along with QUS to evaluate the recovery of bone after the starting of menses or weaning period.

• Single Energy Photon Absorptiometry (SPA): This is done to study bone mineral changes.

• Dual Energy Photon Absorptiometry (DPA): This uses dual energy to study bone density changes.

The DEXA study is unsatisfactory due to the change in magnitude and differences in measurement variability at different body parts. Hence, further studies must be conducted to evaluate the BMD.

Conclusion:

Mothers who breastfeed their children lose around ten percent of their body mass index (BMI). The rate of bone loss is dependent on the amount of milk secreted. Depletion of BMD in women occurs mostly at the time of menopause. Events like pregnancy and lactation have fewer influences on bone mineral density as the body retains its bone strength post-delivery. It is observed that women who breastfeed for a longer duration showed slower recovery of BMD, especially in the lumbar spine and femoral neck. Exposure to any drugs like corticosteroids and oral contraceptives which interfere with BMD should be avoided.