Role of calciotrophic hormones in calcium mobilization of lactation

Bone turnover in lactating and nonlactating women

PURPOSE

During lactation, bone turnover increases, reflecting the mobilization of Calcium from maternal skeletal stores and resulting in bone loss. However, mechanisms are not yet fully understood, and previous studies have been comparatively small. We aim to assess bone metabolism during lactation by comparing bone-metabolism-related-parameters between large cohorts of lactating and nonlactating women.

METHODS

In a retrospective cohort study, we recruited 779 postpartum women and 742 healthy, nonpregnant, nonlactating controls. Postpartum women were examined 3 and 6 months after delivery and retrospectively assigned to either the exclusively breastfeeding (exc-bf) group if they had exclusively breastfed or the nonexclusively breastfeeding (nonexc-bf) group if they had not exclusively breastfed up to the respective visit. Serum levels of PTH, Estradiol, total Calcium, Phosphate, and bone turnover markers (ßCTX, P1NP, Osteocalcin) were compared between the groups.

RESULTS

Bone turnover markers were significantly increased in exc-bf and nonexc-bf women compared with the controls (all ps < .001). ßCTX was approximately twice as high in exc-bf women than in the controls. PTH levels were marginally higher in exc-bf (p < .001) and nonexc-bf women (p = .003) compared with the controls (6 months). Estradiol was suppressed in exc-bf women compared with the controls (p < .001, 3 months).

CONCLUSION

Exc-bf and even nonexc-bf states are characterized by an increase in bone formation and resorption markers. The PTH data distribution of exc-bf, nonexc-bf, and control groups in the underpart of the reference range suggest that lactational bone loss is relatively independent of PTH.

The Serotonergic System and Bone Metabolism During Pregnancy and Lactation and the Implications of SSRI Use on the Maternal-Offspring Dyad

Lactation is a physiological adaptation of the class Mammalia and is a product of over 200 million years of evolution. During lactation, the mammary gland orchestrates bone metabolism via serotonin signaling in order to provide sufficient calcium for the offspring in milk. The role of serotonin in bone remodeling was first discovered over two decades ago, and the interplay between serotonin, lactation, and bone metabolism has been explored in the years following. It is estimated that postpartum depression affects 10-15% of the population, and selective serotonin reuptake inhibitors (SSRI) are often used as the first-line treatment. Studies conducted in humans, nonhuman primates, sheep, and rodents have provided evidence that there are consequences on both parent and offspring when serotonin signaling is disrupted during the peripartal period; however, the long-term consequences of disruption of serotonin signaling via SSRIs during the peripartal period on the maternal and offspring skeleton are not fully known. This review will focus on the relationship between the mammary gland, serotonin, and bone remodeling during the peripartal period and the skeletal consequences of the dysregulation of the serotonergic system in both human and animal studies.

Pharmaceutical treatment of bone loss: From animal models and drug development to future treatment strategies

Animal models are fundamental to advance our knowledge of the underlying pathophysiology of bone loss and to study pharmaceutical countermeasures against it. The animal model of post-menopausal osteoporosis from ovariectomy is the most widely used preclinical approach to study skeletal deterioration. However, several other animal models exist, each with unique characteristics such as bone loss from disuse, lactation, glucocorticoid excess, or exposure to hypobaric hypoxia. The present review aimed to provide a comprehensive overview of these animal models to emphasize the importance and significance of investigating bone loss and pharmaceutical countermeasures from perspectives other than post-menopausal osteoporosis only. Hence, the pathophysiology and underlying cellular mechanisms involved in the various types of bone loss are different, and this might influence which prevention and treatment strategies are the most effective. In addition, the review sought to map the current landscape of pharmaceutical countermeasures against osteoporosis with an emphasis on how drug development has changed from being driven by clinical observations and enhancement or repurposing of existing drugs to today's use of targeted anti-bodies that are the result of advanced insights into the underlying molecular mechanisms of bone formation and resorption. Moreover, new treatment combinations or repurposing opportunities of already approved drugs with a focus on dabigatran, parathyroid hormone and abaloparatide, growth hormone, inhibitors of the activin signaling pathway, acetazolamide, zoledronate, and romosozumab are discussed. Despite the considerable progress in drug development, there is still a clear need to improve treatment strategies and develop new pharmaceuticals against various types of osteoporosis. The review also highlights that new treatment indications should be explored using multiple animal models of bone loss in order to ensure a broad representation of different types of skeletal deterioration instead of mainly focusing on primary osteoporosis from post-menopausal estrogen deficiency.

Low pre-pregnant body mass index is a risk factor for the decrease of postpartum bone mineral density in systemic lupus erythematosus patients received glucocorticoid therapy

OBJECTIVES

This study investigated postpartum bone mineral density (BMD) in patients with systemic lupus erythematosus (SLE) receiving long-term glucocorticoid (GC) therapy, assessed risk factors for decreased postpartum BMD, and evaluated change of BMD after postpartum initiation or restarting of osteoporosis drugs.

METHODS

We retrospectively examined 30 SLE patients who gave birth and 31 non-pregnant SLE patients. In the postpartum SLE patients, BMD was measured after delivery and 1 year later. Multivariate analyses were performed to assess risk factors for decreased BMD in postpartum SLE patients.

RESULTS

Patient age at pregnancy was 34.5 ± 4.5 years, and SLE duration was 9.7 ± 6.0 years. The mean prednisolone dose was 9.7 ± 3.2 mg/day. Body mass index (BMI) was 21.6 ± 2.2 kg/m², with 13 women (43%) experiencing their first delivery. Postpartum BMD was 1.080 ± 0.120 g/cm² in the lumbar spine and 0.834 ± 0.109 g/cm² in the total hip. Bone loss occurred in six patients (21%) in the lumbar spine and 11 patients (37%) in the total hip. Postpartum lumbar spine BMD was significantly reduced compared to that in the non-pregnant group (1.143 ± 0.120 g/cm², p = 0.048). Multivariate analysis identified gestational age and low BMI before pregnancy as risk factors for hip bone loss.

CONCLUSION

Postpartum BMD significantly decrease in SLE patients receiving long-term GC, and low BMI before pregnancy was a risk factor for the decrease. Preconception care to prevent osteoporosis and that regularly monitors BMD after delivery are needed.

Vegetarian diets during pregnancy: effects on the mother's health. A systematic review

While interest in vegetarian nutrition has been steadily increasing, some aspects have not yet been consistently investigated. One topic requiring evidence-based confirmation is the adoption of a vegetarian diet during pregnancy and lactation. Maternal diet is not only correlated with the fetus's and infant's health, but appears relevant for that of the mother as well. Not only is an adequate delivery of nutrients to the fetus and infant mandatory, but the increased physiological needs of the maternal body require an adequate supply of nutrients and can represent harmful stress events that may lead to well-defined pathological conditions. In this review, we aim to systematically investigate state-of-the-art of vegetarian diets during pregnancy and lactation, focusing on maternal nutritional status and pregnancy outcomes. Data are scarce, often inconsistent and not homogeneous for many of the topics we considered, mainly because only a few studies have been performed in developed countries, whereas other studies have derived from developing countries, where vegetarianism can be a proxy indicator of malnutrition. For this reason, we did not find sufficient data to provide evidence-based information and recommendations. To date, the available literature does not clearly support a negative impact on the mother's health and pregnancy outcomes, but, analogously with the findings in the vegetarian adult population, an improvement in the quality of studies might facilitate finding more information on the possible positive impact of well-planned vegetarian diets during pregnancy and lactation. More epidemiological and interventional studies are warranted, in order to address the question as to whether vegetarian nutrition represents an advantage for the mother or poses nutritional issues that need further attention.

Pregnancy and lactation, a challenge for the skeleton

In this review we discuss skeletal adaptations to the demanding situation of pregnancy and lactation. Calcium demands are increased during pregnancy and lactation, and this is effectuated by a complex series of hormonal changes. The changes in bone structure at the tissue and whole bone level observed during pregnancy and lactation appear to largely recover over time. The magnitude of the changes observed during lactation may relate to the volume and duration of breastfeeding and return to regular menses. Studies examining long-term consequences of pregnancy and lactation suggest that there are small, site-specific benefits to bone density and that bone geometry may also be affected. Pregnancy- and lactation-induced osteoporosis (PLO) is a rare disease for which the pathophysiological mechanism is as yet incompletely known; here, we discuss and speculate on the possible roles of genetics, oxytocin, sympathetic tone and bone marrow fat. Finally, we discuss fracture healing during pregnancy and lactation and the effects of estrogen on this process.

Vitamin D Metabolism Varies among Women in Different Reproductive States Consuming the Same Intakes of Vitamin D and Related Nutrients

BACKGROUND

The impact of the reproductive state on vitamin D metabolism and requirements is uncertain in part because of a lack of studies with controlled dietary intakes of vitamin D and related nutrients.

OBJECTIVE

We aimed to quantify the impact of the reproductive state on a panel of vitamin D biomarkers among women of childbearing age consuming equivalent amounts of vitamin D and related nutrients.

METHODS

Nested within a feeding study providing 2 doses of choline, healthy pregnant (26-29 wk gestation; n = 26), lactating (5 wk postpartum; n = 28), and control (nonpregnant/nonlactating; n = 21) women consumed a single amount of vitamin D (511 ± 48 IU/d: 311 ± 48 IU/d from diet and 200 IU/d as supplemental cholecalciferol) and related nutrients (1.6 ± 0.4 g Ca/d and 1.9 ± 0.3 g P/d) for 10 wk. Vitamin D biomarkers were measured in blood obtained at baseline and study end, and differences in biomarker response among the reproductive groups were assessed with linear mixed models adjusted for influential covariates (e.g., body mass index, season, race/ethnicity).

RESULTS

At study end, pregnant women had higher (P < 0.01) circulating concentrations of 25-hydroxyvitamin D [25(OH)D; 30%], 1,25-dihydroxyvitamin D [1,25(OH)2D; 80%], vitamin D binding protein (67%), and C3 epimer of 25(OH)D3 (100%) than control women. Pregnant women also had higher (P ≤ 0.04) ratios of 25(OH)D to 24,25-dihydroxyvitamin D [24,25(OH)2D; 40%] and 1,25(OH)2D to 25(OH)D (50%) than control women. In contrast, no differences (P ≥ 0.15) in vitamin D biomarkers were detected between the lactating and control groups. Notably, the study vitamin D dose of 511 IU/d achieved vitamin D adequacy in most participants (95%) regardless of their reproductive state.

CONCLUSIONS

The higher concentrations of vitamin D biomarkers among pregnant women than among control women suggest that metabolic adaptations, likely involving the placenta, transpire to enhance vitamin D supply during pregnancy. The study findings also support the adequacy of the current vitamin D RDA of 600 IU for achieving serum 25(OH)D concentrations ≥50 nmol/L among women differing in their reproductive state. This trial was registered at clinicaltrials.gov as NCT01127022.

Maternal Mineral and Bone Metabolism During Pregnancy, Lactation, and Post-Weaning Recovery

During pregnancy and lactation, female physiology adapts to meet the added nutritional demands of fetuses and neonates. An average full-term fetus contains ∼30 g calcium, 20 g phosphorus, and 0.8 g magnesium. About 80% of mineral is accreted during the third trimester; calcium transfers at 300-350 mg/day during the final 6 wk. The neonate requires 200 mg calcium daily from milk during the first 6 mo, and 120 mg calcium from milk during the second 6 mo (additional calcium comes from solid foods). Calcium transfers can be more than double and triple these values, respectively, in women who nurse twins and triplets. About 25% of dietary calcium is normally absorbed in healthy adults. Average maternal calcium intakes in American and Canadian women are insufficient to meet the fetal and neonatal calcium requirements if normal efficiency of intestinal calcium absorption is relied upon. However, several adaptations are invoked to meet the fetal and neonatal demands for mineral without requiring increased intakes by the mother. During pregnancy the efficiency of intestinal calcium absorption doubles, whereas during lactation the maternal skeleton is resorbed to provide calcium for milk. This review addresses our current knowledge regarding maternal adaptations in mineral and skeletal homeostasis that occur during pregnancy, lactation, and post-weaning recovery. Also considered are the impacts that these adaptations have on biochemical and hormonal parameters of mineral homeostasis, the consequences for long-term skeletal health, and the presentation and management of disorders of mineral and bone metabolism.

The effects of different levels of calcium supplementation on the bone mineral status of postpartum lactating Chinese women: a 12-month randomised, double-blinded, controlled trial

Increasing dietary Ca intake may prevent the excessive mobilisation of bone mineral in nursing mothers. We aimed to investigate whether higher Ca intake could positively modulate the bone mineral changes in Chinese postpartum lactating women. The study was a 12-month randomised, double-blinded, parallel group trial conducted over 12 months. A total of 150 postpartum women were randomly selected to receive either 40 g of milk powder containing 300 mg of Ca and 5 μg of vitamin D (Low-Ca group) or same milk powder additionally fortified with 300 mg of Ca (Mid-Ca group) or 600 mg of Ca (High-Ca group). Bone mineral density (BMD) for the whole body, the lumbar spine, the total left hip and its sub-regions was measured using dual-energy X-ray absorptiometry. A total of 102 subjects completed the whole trial. The duration of total lactating time was 7·9 (sd 2·8) months on average. The intention-to-treat analysis yielded the following mean percentage changes in BMD for the whole body, the lumbar spine and the total left hip, respectively: −0·93 (sd 1·97), 2·11 (sd 4·90) and −1·60 (sd 2·65) % for the Low-Ca group; −0·56 (sd 1·89), 2·21 (sd 3·77) and −1·43 (sd 2·30) % for the Mid-Ca group; and −0·44 (sd 1·67), 2·32 (sd 4·66) and −0·95 (sd 4·08) % for the High-Ca group. The differences between the groups were not statistically significant (P: 0·5–0·9). The results of the complete case analysis were similar. In sum, we found no significant differences in the bone mineral changes from baseline to 12 months in postpartum lactating women consuming milk powder fortified with different levels of Ca.

Building healthy bones throughout life: an evidence-informed strategy to prevent osteoporosis in Australia

Osteoporosis imposes a tremendous burden on Australia: 1.2 million Australians have osteoporosis and 6.3 million have osteopenia. In the 2007–08 financial year, 82 000 Australians suffered fragility fractures, of which > 17 000 were hip fractures. In the 2000–01 financial year, direct costs were estimated at $1.9 billion per year and an additional $5.6 billion on indirect costs. Osteoporosis was designated a National Health Priority Area in 2002; however, implementation of national plans has not yet matched the rhetoric in terms of urgency. Building healthy bones throughout life, the Osteoporosis Australia strategy to prevent osteoporosis throughout the life cycle, presents an evidence-informed set of recommendations for consumers, health care professionals and policymakers. The strategy was adopted by consensus at the Osteoporosis Australia Summit in Sydney, 20 October 2011. Primary objectives throughout the life cycle are: to maximise peak bone mass during childhood and adolescence to prevent premature bone loss and improve or maintain muscle mass, strength and functional capacity in healthy adults to prevent and treat osteoporosis in order to minimise the risk of suffering fragility fractures, and reduce falls risk, in older people. The recommendations focus on three affordable and important interventions — to ensure people have adequate calcium intake, vitamin D levels and appropriate physical activity throughout their lives. Recommendations relevant to all stages of life include: daily dietary calcium intakes should be consistent with Australian and New Zealand guidelines serum levels of vitamin D in the general population should be above 50nmol/L in winter or early spring for optimal bone health regular weight-bearing physical activity, muscle strengthening exercises and challenging balance/mobility activities should be conducted in a safe environment.

FGF-21 and skeletal remodeling during and after lactation in C57BL/6J mice

Lactation is associated with significant alterations in both body composition and bone mass. Systemic and local skeletal factors such as receptor activator of nuclear factor κ-B ligand (RANKL), PTHrP, calcitonin, and estrogen are known to regulate bone remodeling during and after lactation. Fibroblast growth factor 21 (FGF-21) may function as an endocrine factor to regulate body composition changes during lactation by inducing gluconeogenesis and fatty acid oxidation. In this study, we hypothesized that the metabolic changes during lactation were due in part to increased circulating FGF-21, which in turn could accentuate bone loss. We longitudinally characterized body composition in C57BL/6J (B6) mice during (day 7 and day 21 of lactation) and after normal lactation (day 21 postlactation). At day 7 of lactation, areal bone density declined by 10% (P < .001), bone resorption increased (P < .0001), percent fat decreased by 20%, energy expenditure increased (P < .01), and markers of brown-like adipogenesis were suppressed in the inguinal depot and in preformed brown adipose tissue. At day 7 of lactation there was a 2.4-fold increase in serum FGF-21 vs baseline (P < .0001), a 8-fold increase in hepatic FGF-21 mRNA (P < .03), a 2-fold increase in undercarboxylated osteocalcin (Glu13 OCn) (P < .01), and enhanced insulin sensitivity. Recovery of total areal bone density was noted at day 21 of lactation, whereas the femoral trabecular bone volume fraction was still reduced (P < .01). Because FGF-21 levels rose rapidly at day 7 of lactation in B6 lactating mice, we next examined lactating mice with a deletion in the Fgf21 gene. Trabecular and cortical bone masses were maintained throughout lactation in FGF-21(-/-) mice, and pup growth was normal. Compared with lactating control mice, lactating FGF-21(-/-) mice exhibited an increase in bone formation, but no change in bone resorption. In conclusion, in addition to changes in calciotropic hormones, systemic FGF-21 plays a role in skeletal remodeling and changes in body composition during lactation in B6 mice.

Calcium economy in human pregnancy and lactation

Pregnancy and lactation are times of additional demand for Ca. Ca is transferred across the placenta for fetal skeletal mineralisation, and supplied to the mammary gland for secretion into breast milk. In theory, these additional maternal requirements could be met through mobilisation of Ca from the skeleton, increased intestinal Ca absorption efficiency, enhanced renal Ca retention or greater dietary Ca intake. The extent to which any or all of these apply, the underpinning biological mechanisms and the possible consequences for maternal and infant bone health in the short and long term are the focus of the present review. The complexities in the methodological aspects of interpreting the literature in this area are highlighted and the inter-individual variation in the response to pregnancy and lactation is reviewed. In summary, human pregnancy and lactation are associated with changes in Ca and bone metabolism that support the transfer of Ca between mother and child. The changes generally appear to be independent of maternal Ca supply in populations where Ca intakes are close to current recommendations. Evidence suggests that the processes are physiological in humans and that they provide sufficient Ca for fetal growth and breast-milk production, without relying on an increase in dietary Ca intake or compromising long-term maternal bone health. Further research is needed to determine the limitations of the maternal response to the Ca demands of pregnancy and lactation, especially among mothers with marginal and low dietary Ca intake, and to define vitamin D adequacy for reproductive women.

Calcium and bone metabolism disorders during pregnancy and lactation

Pregnancy and lactation cause a substantial increase in demand for calcium that is met by different maternal adaptations within each period. Intestinal calcium absorption more than doubles during pregnancy, whereas the maternal skeleton resorbs to provide most of the calcium content of breast milk during lactation. These maternal adaptations also affect the presentation, diagnosis, and management of disorders of calcium and bone metabolism. Although some women may experience fragility fractures as a consequence of pregnancy or lactation, for most women, parity and lactation do not affect the long-term risks of low bone density, osteoporosis, or fracture.

Vitamin D in pregnancy and lactation in humans

Concerns exist about the adequacy of vitamin D in pregnant and lactating women. This review assesses the evidence that maternal vitamin D status influences maternal, fetal, and breast-fed infant bone health; maternal adverse outcomes (preeclampsia, gestational diabetes, obstructed labor, and infectious disease); fetal adverse outcomes (growth, gestational age, and developmental programming); and infant adverse outcomes. The evidence for all of these outcomes is contradictory (except for maternal infectious disease) and lacking causality; thus, it is inconclusive. The 2011 Dietary Reference Intakes for vitamin D and their implications for assessing vitamin D status are discussed. An estimated 5% to 29% of American pregnant women may have inadequate vitamin D status, with the higher prevalence in African Americans. Little is known about the prevalence of inadequacy in American lactating women. Research needs are also identified, especially the need for rigorous and well-designed randomized clinical trials to determine the role of vitamin D in nonbone health outcomes in pregnancy and lactation.

Vitamin D: a growing perspective

Vitamin D deficiency has been widely reported in all age groups in recent years. Rickets has never been eradicated in developed countries, and it most commonly affects children from recent immigrant groups. There is much evidence that current vitamin D guidelines for the neonatal period, 5-10 microg (200-400 IU)/day, prevent rickets at the typical calcium intakes in developed countries. The annual incidence of vitamin D-deficiency rickets in developed countries ranges between 2.9 and 7.5 cases per 100,000 children. The prevalence of vitamin D deficiency in mothers and their neonates is remarkable, and the results of one study suggest that third-trimester 25-hydroxyvitamin D (25(OH)D) is associated with fetal bone mineral accrual that may affect prepubertal bone mass accumulation. Beyond infancy, the evidence indicates that 5 microg (200 IU)/day of vitamin D has little effect on vitamin D status as measured by the serum 25(OH)D concentration. Two randomized clinical trials show that higher vitamin D intake improves one-year gain in bone density in adolescent girls. The functions of vitamin D extend beyond bone to include immune system regulation and anti-proliferative effects on cells. Early life vitamin D inadequacy is implicated in the risk of bone disease, autoimmune disease, and certain cancers later in life; however, long-term interventional studies do not exist to validate the widespread implementation of greater vitamin D consumption. Here we review the available data concerning vitamin D status and health effects of vitamin D in pregnancy through to and including adolescence.

Vitamin D in pregnancy and lactation: maternal, fetal, and neonatal outcomes from human and animal studies

During pregnancy and lactation, mothers require significant amounts of calcium to pass on to the developing fetus and suckling neonate, respectively. Given the dependence of adult calcium concentrations and bone metabolism on vitamin D, one might anticipate that vitamin D sufficiency would be even more critical during pregnancy and lactation. However, maternal adaptations during pregnancy and lactation and fetal adaptations provide the necessary calcium relatively independently of vitamin D status. It is the vitamin D-deficient or insufficient neonate who is at risk of problems, including hypocalcemia and rickets. Due to poor penetrance of vitamin D and 25-hydroxyvitamin D [25(OH)D] into milk, exclusively breastfed infants are at higher risk of vitamin D deficiency than are formula-fed infants. Dosing recommendations for women during pregnancy and lactation might be best directed toward ensuring that the neonate is vitamin D-sufficient and that this sufficiency is maintained during infancy and beyond. A dose of vitamin D that provides 25(OH)D sufficiency in the mother during pregnancy should provide normal cord blood concentrations of 25(OH)D. Research has shown that during lactation, supplements administered directly to the infant can easily achieve vitamin D sufficiency; the mother needs much higher doses (100 mug or 4000 IU per day) to achieve adult-normal 25(OH)D concentrations in her exclusively breastfed infant. In addition, the relation (if any) of vitamin D insufficiency in the fetus or neonate to long-term nonskeletal outcomes such as type 1 diabetes and other chronic diseases needs to be investigated.

Plasma parathyroid hormone-related peptide and bone metabolism in periparturient dairy cows

The first weeks of lactation in dairy cows are characterised by elevated bone resorption. The connection between lactation and bone metabolism is still much discussed. In this work, changes in the concentration of plasma parathyroid hormone-related peptide (PTHrP) and markers of bone metabolism were studied in Holstein cows and heifers in the dry period and early lactation to determine the role of PTHrP in the relationship between the rate of bone remodelling and the onset of lactation in dairy cows. Blood samples were taken 14 days before calving ('D-14', n = 23) and then on day 10 ('D+10', n = 21) and day 30 after calving ('D+30', n = 23). Using enzyme immunoassay (EIA), the concentrations of PTHrP, parathyroid hormone (PTH), carboxyterminal cross-linked telopeptide of type I collagen (CTX) and oestradiol and the activity of bone specific alkaline phosphatase (BSALP) were determined. The results showed a statistically significant increase in plasma PTHrP (p < 0.005) and CTX (p < 0.0001) in cows on 'D+10' as compared to 'D-14' and CTX on 'D+30' as compared to 'D-14' (p < 0.0001). Significant negative correlations were found between the concentrations of PTHrP and oestradiol (r = -0.29, p < 0.05) and those of CTX and oestradiol (r = -0.54, p < 0.0001). In nonpregnant heifers (n = 6), the concentration of CTX and the activity of BSALP were significantly higher (p < 0.0001) than in dry cows. The observed increments of PTHrP and bone resorption after parturition reveal adaptations of bone metabolism to lactation in dairy cows.

Postpartum vitamin D insufficiency and secondary hyperparathyroidism in healthy Danish women

OBJECTIVE

To examine vitamin D status and parathyroid function in normal Danish women postpartum.

DESIGN

Three cross-sectional measures during follow-up of 89 women postpartum.

SUBJECTS AND INTERVENTION

We assessed vitamin D status by measuring plasma 25-hydroxyvitamin D (P-25OHD) and the degree of secondary hyperparathyroidism by measuring plasma parathyroid hormone (P-PTH) in 89 Caucasian women at three consecutive visits: (mean (range)) 23 (10-37) days (spring), 117 (95-140) days (late summer) and 274 (254-323) days (winter) postpartum.

RESULTS

P-25OHD showed seasonal variations with higher values in late summer than in the other periods (P < 0.001). At the first visit, 65% received vitamin D supplements. At the following visits, almost 50% were supplemented. Vitamin D insufficiency (P-25OHD < 50 nmol/l) occurred more often during winter (28%) than in spring (14%) (Fisher's exact test, P = 0.02) or late summer (7%) (P = 0.0001). Irrespective of season, vitamin D insufficiency occurred most frequent in women who did not take vitamin D supplements (Fisher's exact test, P < 0.02). Frank vitamin D deficiency (P-25OHD < 25 nmol/l) was observed during winter in 6%. At all three periods, P-25OHD correlated inversely with P-PTH indicating secondary hyperparathyroidism at deficient vitamin D status. During spring, late summer and winter three, one and four females, respectively, had elevated plasma PTH.

CONCLUSION

Vitamin D insufficiency with secondary hyperparathyroidism is a frequent finding in healthy Danish women postpartum and especially during winter. Vitamin D supplements reduced the risk of vitamin D insufficiency, especially during winter. Our results support the importance of increased alertness regarding information of pregnant and lactating women about vitamin D supplements. Furthermore, it has to be studied whether the present recommendations of an intake of 5-10 microg vitamin D/day are sufficient, especially during winter months.

The relationship between parity and bone mineral density in women characterized by a homogeneous lifestyle and high parity

CONTEXT

We reported previously that Old Order Amish (OOA) women have fewer hip fractures and higher bone mineral density (BMD) than non-Amish Caucasian women.

OBJECTIVE

The objective of this study was to determine whether the high parity characteristic of OOA women contributes to their relative bone health. Previous data on the long-term effects of parity on BMD have yielded conflicting results with few data from very high parity populations. This observational study included participants in the Amish Family Osteoporosis Study, begun in 1997 to identify genetic and clinical determinants of osteoporosis in the OOA. We measured BMD by dual-energy x-ray absorptiometry at the spine, hip, and distal radius in 424 parous OOA women aged 40 and older (mean age, 57.7 +/- 12 yr; mean parity, 7.6 +/- 2.9).

RESULTS

Increasing parity was associated with later menopause (P = 0.001) and modestly, but not significantly, higher body mass index (BMI) (P = 0.09). Increasing parity was associated with higher BMD at the total hip and trochanter (age-adjusted P = 0.02 and 0.03), no longer statistically significant after accounting for BMI. Among women aged 50-59 yr, parity was strongly associated with BMD even after accounting for age and BMI (age-adjusted P = 0.02), although this was not true for women younger than 50 or at least 60 yr old.

CONCLUSIONS

We conclude that high parity is associated with increased hip BMD in OOA women, largely mediated by higher BMI. The parity-hip BMD association remained statistically significant after accounting for age and BMI only in women aged 50-59 yr, partially explained by a later menopausal age with high parity. The benefit of high parity on BMD appeared to be lost soon after the menopausal transition, and, therefore, these data provide evidence of neither a detrimental nor beneficial effect of high parity on long-term bone health.

Bone mineral density and calcium metabolism of Hong Kong Chinese postpartum women—a 1-y longitudinal study

OBJECTIVE

This paper reports longitudinal changes in bone mineral density (BMD), calcium homeostasis and dietary calcium intake in a group of Hong Kong breastfeeding women during the first year postpartum.

DESIGN AND SUBJECTS

Nine mothers who breastfed exclusively or almost exclusively for at least 3 months and 14 formula feeding mothers aged 20-40 y were interviewed after delivery, 2 and 6 weeks, 3, 6 and 12 months postpartum. BMD at L2-L4 lumbar spine (LS), trochanter (Tro) and femoral neck (FN), serum intact parathyroid hormone (iPTH), serum bone-specific alkaline phosphatase (b-ALP), urinary deoxypyridinoline (Dpd), serum and urinary calcium (Ca) and phosphorus (P) and dietary intake of macronutrients were assessed.

RESULTS

Compared to the formula feeding group, BMD assessed at LS, Tro and FN decreased significantly in the breastfeeding group over the first 6 months, with rebound to approximate baseline values at 12 months for the latter two sites. Serum iPTH increased in both groups, whereas serum b-ALP was consistently higher in the breastfeeders. Urinary Ca and P excretion decreased early postpartum in both groups, but the breastfeeders had higher excretion at 3 and 6 months. Breastfeeding mothers consumed significantly more Ca than the formula feeding mothers in the early postpartum.

CONCLUSIONS

Increased calcium requirement during early lactation is affected through mobilisation of bone and renal calcium conservation. Bone mineral loss during lactation is temporary. Further studies are warranted to investigate the effects of diet and other hormonal factors on the calcium homeostasis during lactation.

Calcium sensing by the mammary gland

Calcium is an important nutrient that is secreted into milk in quantities that put a considerable stress upon maternal calcium homeostasis. Here we summarize the evidence that two important entities, the extracellular calcium-sensing receptor (CaR) and parathyroid hormone-related protein (PTHrP) are involved in a feedback loop that regulates calcium fluxes to the mammary gland. The CaR may also play a role in regulating milk secretion, and may regulate the proliferation of normal and neoplastic mammary epithelial cells. Finally, the relationship between the CaR and PTHrP in breast cancer cells may promote the formation of osteolytic bone metastases.

Reduced expression of the PTH/PTHrP receptor during development of the mammary gland influences the function of the nipple during lactation

Signaling by the parathyroid hormone/parathyroid hormone-related protein receptor (Ppr) is necessary for mammary gland development beyond the early induction stage in mice. We used a series of murine models of reduced Ppr expression to determine how diminished receptor signaling influences mammary development. Reduction of Ppr expression to very low levels prevented mammary gland development. A less-severe reduction in Ppr expression permitted progression of mammary gland development beyond the induction stage, but the nipples of these mice were dramatically smaller than those of controls, with altered epidermis and connective tissue. Mothers with reduced expression of Ppr could not successfully nurse pups; however, the lactating glands did produce milk but could not efficiently deliver it. This finding was associated with reduced levels of matrix metalloproteinase-2 and an absence of pregnancy-associated remodeling of connective tissue matrix in the nipple. Reduced smooth muscle appears to underlie the majority of nipple deficiencies in mice with lower levels of the Ppr expression.

Mammary-specific deletion of parathyroid hormone-related protein preserves bone mass during lactation

Large amounts of calcium are transferred to offspring by milk. This demand results in negative calcium balance in lactating mothers and is associated with rapid bone loss. The mechanisms of bone loss during lactation are only partly understood. Several studies have suggested that parathyroid hormone-related protein (PTHrP) might be secreted into the circulation by the lactating mammary gland and regulate bone turnover during lactation. Because mammary development fails in the absence of PTHrP, conventional PTHrP knockout mice cannot be used to address this possibility. To examine this hypothesis, we therefore used mice carrying a beta-lactoglobulin promoter-driven Cre transgene, one null PTHrP allele, and one floxed PTHrP allele. Expression of Cre specifically in mammary epithelial cells during late pregnancy and lactation resulted in efficient deletion of the PTHrP gene; mammary gland PTHrP mRNA and milk PTHrP protein were almost completely absent. Removal of PTHrP from the lactating mammary glands resulted in reductions in levels of circulating PTHrP and 1,25-dihydroxy vitamin D and urinary cAMP. In addition, bone turnover was reduced and bone loss during lactation was attenuated. We conclude that during lactation mammary epithelial cells are a source of circulating PTHrP that promotes bone loss by increasing rates of bone resorption.

Effects of Nutrient and Food Intake on Calcaneous Bone Mass among Healthy Japanese Women in the Predelivery and Postpartum Periods

OBJECTIVE

To clarify the dietary factors affecting change in calcaneous bone mass during the predelivery and postpartum periods in healthy Japanese women.

METHODS

The calcaneous bone mass was measured as the osteo sono-assessment index (OSI) using the quantitative ultrasound method in 76 Japanese women who were pregnant between February and June 2000. These women subsequently experienced normal pregnancy and labor and could be followed until the sixth month after delivery at an obstetrics and gynecology clinic center located in metropolitan Tokyo. After the intraindividual changes in the OSI during the follow-up period were determined, the relationship between the OSI or OSI change from gestation to the postpartum period and the estimates of nutrient and food intake obtained using a 140-item semiquantitative food frequency questionnaire (FFQ) were analyzed using stepwise multiple regression analysis.

RESULTS

Iron intake in gestation was a significant positive correlate with the percentage change in the OSI between week 36 of gestation and day 5 after delivery (p < 0.001) and that between week 36 of gestation and month 6 after delivery (p < 0.001) (partial regression coefficient of energy-adjusted iron intake, beta = 0.493 mg/day and 0.342 mg/day, respectively). Intake of vitamin D and fruits and vegetables during gestation and/or postpartum was positively associated with the OSI change from week 36 of gestation to the postdelivery stage, whereas the OSI change was inversely related to the intake of carotene, sodium chloride, and meat in the gestation or postpartum period.

CONCLUSIONS

Sufficient intake of iron, vitamin D, or fruits and vegetables may be important for the preservation of bone mass after delivery.

Micronutrients and the bone mineral content of the mother, fetus and newborn

The fluxes of the primary bone-forming minerals, calcium, phosphorus, magnesium and zinc, across the placenta and through breast milk place considerable demands on maternal mineral economy. Increases in food consumption, elevated gastrointestinal absorption, decreased mineral excretion and mobilization of tissue stores are several possible biological strategies for meeting these extra mineral requirements. This paper presents a review of the evidence on the extent to which these strategies apply in the human situation, the mechanisms by which they occur, the limitations imposed by maternal diet and vitamin D status and the possible consequences for the growth of the infant and bone health of the mother. On the strength of current evidence it appears that pregnancy and lactation are associated with physiological adaptive changes in mineral metabolism that are independent of maternal mineral supply within the range of normal dietary intakes. These processes provide the minerals necessary for fetal growth and breast milk production without requiring an increase in maternal dietary intake or compromising maternal bone health in the long term. This may not apply to pregnant women whose mineral intakes or sunlight exposure are marginal. As a vehicle for promoting optimal growth and bone mineral content of infants, supplementation of lactating women with minerals or vitamin D is unlikely to prove effective. The situation in pregnancy is less certain. Until more studies have been conducted, a precautionary case can be made for targeted supplementation of pregnant women who have very low intakes of calcium or who are at risk of vitamin D deficiency.

Negative calcium balance during lactation in rural Mexican women

BACKGROUND

Additional calcium is required during lactation, and several calcium regulatory factors are involved in calcium balance. In lactating rural women who have marginal nutrition and consume a high-fiber diet, negative calcium balance may be expected.

OBJECTIVE

We evaluated calcium balance and its association with potential calcium regulatory factors in lactating, rural Mexican women who had marginal nutrition and consumed a high-fiber diet.

DESIGN

This cross-sectional study included women at 1, 3, 6, and 12 mo of lactation (L1, L3, L6, and L12 groups) and women who had weaned their infants (W group). Age-matched, nonlactating women (NL group) were also included. Calcium balance and concentrations of calcium regulatory factors were determined. Correlation analysis was performed by using data from all of the lactating women.

RESULTS

Calcium balance in the L1, L3, and L6 groups was negative and was significantly different (P < 0.05) from that in the W and NL groups. Serum parathyroid hormone (PTH) and 1,25-dihydroxyvitamin D [1,25-(OH)(2)D] concentrations were significantly higher (P < 0.05) in the W group than in the L and NL groups. Calcium balance was positively associated with serum estradiol concentrations (r = 0.58, P < 0.05) and negatively associated with serum 1,25-(OH)(2)D concentrations (r = -0.52, P < 0.05). Breast-milk calcium concentrations correlated positively with serum PTH-related peptide (PTHrP) concentrations (r = 0.51, P < 0.05) and negatively with serum estradiol concentrations (r = -0.57, P < 0.05).

CONCLUSIONS

Negative calcium balance was observed during lactation in rural Mexican women who consumed a high-fiber diet. Furthermore, the data suggest that the hormones estradiol and PTHrP are involved in the regulation of calcium balance and of the calcium content of milk during lactation.

Calcium in pregnancy and lactation

Pregnancy and lactation are periods of high calcium requirement. This review highlights recent advances in our understanding of calcium and bone metabolism during human pregnancy and lactation and discusses the findings in relation to the calcium nutrition of the mother. The evidence indicates that pregnancy and lactation are characterized by physiological adaptive processes that are independent of maternal calcium intake and that provide the calcium necessary for fetal growth and breast-milk production without requiring an increase in maternal calcium intake. There are firm data that demonstrate that a low calcium intake during lactation does not lead to impaired lactational performance or to exaggerated bone loss. However, more research is required to define whether a low calcium intake prior to or during pregnancy can have deleterious effects on reproductive and lactational performance, and on the long-term health of the mother and child.

Lactation and lead body burden turnover: a pilot study in Mexico

A pilot study was conducted in Morelos, Mexico in March 1999 to assess the body burden of lead in 24 Mexican women of childbearing age. Lead levels were measured in whole blood and at three bone sites: two primarily trabecular (calcaneus and patella) and one primarily cortical (tibia). Demographic and reproductive characteristics of the women and potential sources of lead exposure were gathered by a direct interview. An inverse relationship was noted between months of lactation and age-adjusted calcaneus lead level (P = 0.001). No association was observed between age-adjusted patella or tibia lead level and months of lactation (P = 0.15). Blood lead levels were positively associated with the use of lead-glazed ceramics (P = 0.01). Bone and blood lead levels were observed to be 77% higher in these rural Mexican women than in urban New York City women. This pilot study provides further limited evidence for the hypothesis that lead mobilization occurs during lactation.

The parathyroid hormone-related protein

Many physiologic roles of PTHrP are emerging. The protein functions locally in diverse tissues, often regulating the entry of cells into a differentiation pathway or acting as an epithelial signal in epithelial-mesenchymal interactions. To carry out these functions, PTHrP uses the receptor it shares with PTH or one of several PTHrP receptors that have evolved to recognize selectively the PTH-like region of PTHrP or other domains. Thus, PTHrP is a polyhormone. An exquisite selectivity barrier allows PTHrP to carry out its local tissue functions at the same time PTH uses their shared receptor to regulate systemic calcium homeostasis. This barrier is breached under pathologic circumstances, such as when malignant tumors secrete enough PTHrP into blood to cause PTH-like effects, including hypercalcemia. Powerful genetic models that have been developed in the past 7 years promise to give continuing insights into the physiology and pathophysiology of PTHrP.

Lower peak bone mass and its decline

There is evidence that two-thirds of the risk of osteoporotic fracture can be predicted from the pre-menopausal bone mineral density. The frequency of osteoporosis in older women may be modifiable by implementing invention strategies in the pre- and peri-menopausal periods. Lower peak bone mineral density and bone loss can be identified in women with altered reproductive hormone or calciotrophic hormone concentrations, or selected lifestyle practices. Alterations in reproductive hormones may occur in adolescence (from an early age of pregnancy or the amenorrhoea of anorexia nervosa or exercise), in the pre-menopause (nulliparity, oophorectomy, early ovarian failure or marginal hormonal status) or in the peri-menopause. Alterations in calciotrophic hormone concentrations include corticosteroid therapy and breast cancer treatment. Lifestyle risk factors include the misuse of alcohol and possibly smoking, physical inactivity or an imbalance in dietary intake. Effective intervention currently consists of treating underlying conditions and monitoring high-risk groups.

Maternal calcium metabolism and bone mineral status

Human pregnancy is associated with major changes in calcium and bone metabolism and in bone mineral status before and after gestation. The changes are compatible with the uptake and mobilization of calcium by the maternal skeleton to meet the high requirement for fetal growth and for breast-milk production. Breast-feeding is accompanied by decreases in bone mineral status, increases in bone turnover rate, and reductions in urinary calcium excretion. These effects are reversed during and after weaning, and, in several skeletal regions, bone mineral content ultimately exceeds that measured after delivery. By 3-6 mo after lactation, the postpartum changes in bone mineral status of women who breast-feed largely match those of women who do not, regardless of the duration of lactation. No consistent picture has emerged of the effect of pregnancy on bone mineral status, although increases in bone turnover, calcium absorption, and urinary calcium excretion are well recognized. Events before conception may modify the bone response, particularly if conception occurs within a few months of a previous pregnancy or lactation. There is no evidence that the changes observed during lactation reflect inadequacies in calcium intake. Supplementation studies have shown that neither the bone response nor breast-milk calcium secretion is modified by increases in calcium supply during lactation, even in women with a low calcium intake. The situation in pregnancy is less clear. Calcium nutrition may influence the health of the pregnant woman, her breast-milk calcium concentration, and the bone mineralization and blood pressure of her infant, but these possibilities require formal testing.

Increased intracortical bone remodeling during lactation in beagle dogs

There are substantial changes in skeletal and mineral metabolism during pregnancy and lactation. The purpose of this study was to determine the changes in intracortical bone remodeling and turnover during lactation in beagle dogs. A femur and rib were obtained from dogs near the end of lactation or soon after weaning and compared with nonlactating controls. Rib cortical bone had much higher bone turnover rates than did femoral diaphyseal cortical bone. The number of single-labeled osteons and the number of resorption spaces were significantly greater during lactation in both the rib and the femur. Additionally, the mineral apposition rate, basic multicellular unit activation frequency, and bone turnover rates were greater in the femoral cortical bone from the lactating dogs than from the controls. These data demonstrate that during lactation, intracortical bone remodeling increases, and this may provide a mechanism for the skeleton to be responsive to the calcium requirements of the mother. In addition, these data may help explain the transient decreases in cortical bone mineral density that are reported to occur during human lactation.

The role of calcium in health and disease

Skeletal fragility at the end of the life span (osteoporosis) is a major source of morbidity and mortality. Adequate calcium intake from childhood to the end of the life span is critical for the formation and retention of a healthy skeleton. High intakes of calcium and vitamin D potentiate the bone loss prevention effects of hormone replacement therapy in postmenopausal women. Pregnancy and lactation are not risk factors for skeletal fragility, although lactation is associated with a transient loss of bone that cannot be prevented by calcium supplementation. Low calcium intake has been implicated in the development of hypertension, colon cancer, and premenstrual syndrome, and it is associated with low intakes of many other nutrients. Encouragement of increased consumption of calcium-rich foods has the potential to be a cost-effective strategy for reducing fracture incidence later in life and for increasing patients' dietary quality and overall health.