Human lactation: forearm trabecular bone loss, increased bone turnover, and renal conservation of calcium and inorganic phosphate with recovery of bone mass following weaning

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.

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.

Reduced bone formation and increased bone resorption drive bone loss in Eimeria infected broilers

Coccidiosis is an economically significant disease in the global poultry industry, but little is known about the mechanisms of bone defects caused by coccidiosis; thus, the study focused on effects of coccidiosis on the bone homeostasis of young broiler chickens. A total of 480 male Cobb500 broilers were randomly allocated into four treatment groups, including an uninfected control consuming diet ad libitum, two infected groups were orally gavaged with two different concentrations of sporulated Eimeria oocysts, and an uninfected pair-fed group fed the same amount of feed as the high Eimeria-infected group consumed. Growth performance and feed intake were recorded, and samples were collected on 6 days post infection. Results indicated that coccidiosis increased systemic oxidative status and elevated immune response in bone marrow, suppressing bone growth rate (P < 0.05) and increasing bone resorption (P < 0.05) which led to lower bone mineral density (P < 0.05) and mineral content (P < 0.05) under Eimeria infection. With the same amount of feed intake, the uninfected pair-fed group showed a distinguished bone formation rate and bone resorption level compared with the Eimeria infected groups. In conclusion, inflammatory immune response and oxidative stress in broilers after Eimeria infection were closely associated with altered bone homeostasis, highlighting the role of inflammation and oxidative stress in broiler bone homeostasis during coccidiosis.

Maternal bone adaptation to mechanical loading during pregnancy, lactation, and post-weaning recovery

The maternal skeleton undergoes dramatic bone loss during pregnancy and lactation, and substantial bone recovery post-weaning. The structural adaptations of maternal bone during reproduction and lactation exert a better protection of the mechanical integrity at the critical load-bearing sites, suggesting the importance of physiological load-bearing in regulating reproduction-induced skeletal alterations. Although it is suggested that physical exercise during pregnancy and breastfeeding improves women's physical and psychological well-being, its effects on maternal bone health remain unclear. Therefore, the objective of this study was to investigate the maternal bone adaptations to external mechanical loading during pregnancy, lactation, and post-weaning recovery. By utilizing an in vivo dynamic tibial loading protocol in a rat model, we demonstrated improved maternal cortical bone structure in response to dynamic loading at tibial midshaft, regardless of reproductive status. Notably, despite the minimal loading responses detected in the trabecular bone in virgins, rat bone during lactation experienced enhanced mechano-responsiveness in both trabecular and cortical bone compartments when compared to rats at other reproductive stages or age-matched virgins. Furthermore, our study showed that the lactation-induced elevation in osteocyte peri-lacunar/canalicular remodeling (PLR) activities led to enlarged osteocyte lacunae. This may result in alterations in interstitial fluid flow-mediated mechanical stimulation on osteocytes and an elevation in solute transport through the lacunar-canalicular system (LCS) during high-frequency dynamic loading, thus enhancing mechano-responsiveness of maternal bone during lactation. Taken together, findings from this study provide important insights into the relationship between reproduction- and lactation-induced skeletal changes and external mechanical loading, emphasizing the importance of weight-bearing exercise on maternal bone health during reproduction and postpartum.

The influence of lactation on BMD measurements and TBS: a 12-month follow-up study

Although lactation is associated with transient bone loss and body weight changes, the unchanged TBS could highlight a limited effectiveness in detecting dynamic bone properties in the first year postpartum.

PURPOSE

To evaluate trabecular bone score (TBS) and bone mineral density (BMD) in postpartum women.

METHODS

This was a 12-month prospective cohort study with 40 lactating postpartum women and 44 non-pregnant women. The inclusion criteria were as follows: aged between 18 and 35 years old, an uncomplicated term (≥37 weeks) pregnancy with a single fetus, and no intention of becoming pregnant within 12 months. BMD measurements, including spine, hip, forearm and whole body, were performed by DXA at four different time points after delivery: (1) 1st month, (2) 3rd-4th month, (3) 6th-9th month, and (4) ≥ 12th month postpartum.

RESULTS

BMD measurements showed a statistically significant decrease at spine (1.134 vs. 1.088 g/cm², p < 0.01), femoral neck (0.988 vs. 0.946 g/cm², p < 0.01), total femur (0.971 vs. 0.933 g/cm², p < 0.01), and whole body (1.132 vs. 1.119 g/cm², p = 0.03) at the 2nd assessment (peak of lactation). There was early spinal recovery after the 3rd assessment with complete recovery in all skeletal sites. Although it has had significant weight loss (67.3 vs. 63.2 kg, p < 0.01) and body mass index reduction (25.2 vs. 23.4, p < 0.01), there was significant increment of spine BMD (1.134 vs. 1.165 g/cm², p < 0.01) after 12-month follow-up. The TBS did not change over time.

CONCLUSIONS

Although lactation is associated with transient bone loss and body weight changes, the unchanged TBS could highlight a limited effectiveness in detecting dynamic bone properties in the first year postpartum.

National guidelines on nutrient reference values for the healthy adult population and for pregnant or lactating women are based on heterogeneous sources of evidence: review of guidelines

Many countries provide dietary guidelines for health practitioners and/or the general population. However, there is no general, international guideline serving as a template for national dietary guidelines, and there is little to no consensus regarding reference values for different nutrients. The present review compared 27 national dietary guidelines for healthy adults as well as for pregnant and/or breastfeeding women, and analysed their quality and the evidence behind their recommendations. The guidelines were evaluated for their quality using the instrument Agree II, and found to be heterogeneous (overall quality score 14%-100%) and often insufficient (quality score < 50%) due to missing information about their methodology and sources of evidence. We analysed the evidence (number of studies, study types and publication years) of reference values of a number of nutrients using the five guidelines that provided the highest scores in the Agree II assessment. The reference values varied among guidelines, were rarely based on up-to-date meta-analyses, and were often based on insufficiently reported evidence (22/27 guidelines with quality score < 50%). We recommend systematic reviews of high quality studies to formulate future guidelines, and to use guidelines on how to write guidelines.

Severe Bone Microarchitecture Impairment in Women With Pregnancy and Lactation-Associated Osteoporosis

Context

Pregnancy- and lactation-associated osteoporosis (PLO) is a rare condition characterized by fragility fractures, mostly vertebral, during the third trimester of pregnancy or the early postpartum period.

Objective

The aim of this study was to evaluate bone microarchitecture in women with PLO to better understand the pathophysiology of this disease.

Methods

In this retrospective study, we included women with PLO referred to our bone center between November 2007 and July 2012. We assessed bone mineral density (BMD) by dual-energy x-ray absorptiometry, bone turnover markers, and bone microarchitecture by high-resolution peripheral quantitative computed tomography. Results were compared with a control group of healthy lactating women.

Results

Of the 7 primiparous patients with PLO, 6 suffered vertebral fractures and 1 developed a hip fracture during the seventh month of gestation. Fractures occurred within the eighth month of pregnancy and the fourth month post partum; vertebral fractures were multiple in 85.7%. Major or minor risk factors for osteoporosis were present in 86% of our patients. Trabecular density, number, and thickness were 34%, 20% and 22% lower than controls (P < .01, P = .01, and P = .01, respectively). Cortical parameters were also deteriorated but to a lesser extent.

Conclusion

In comparison with healthy lactating women, patients with PLO presented severe deterioration of bone trabecular and cortical microarchitecture. This significant compromise may explain the occurrence of multiple fractures in these otherwise healthy young women. Further prospective studies are needed to determine whether bone microarchitecture might be able to be restored in the future.

Secondary osteon variants and remodeling in human bone

Histomorphometric analysis of human cortical bone has documented the occurrence of secondary osteon variants. These include drifting osteons which form tails as they move erratically through the cortex and Type II osteons which show partial resorption and redeposition within the cement line of the osteon. Little is known about the biological significance of these variants. Prior studies suggested correlations with age, biomechanics, diet, and mineral homeostasis. No study has yet tested for osteon variant associations with static measures of bone remodeling. In this study, thin sections (n = 112) of the posterior femur representing a late English Medieval adult human osteological collection, subdivided by age, sex, and socio-economic status, were examined to determine whether remodeling indicators reconstructed from osteon parameters (area, diameter, area ratios) and densities differed between categories of presence or absence of Type II and drifting osteon variants. Of the 112 sections, 33 presented with Type II osteons, and 38 had drifting osteons. Sporadic statistically significant results were identified. Haversian canal:osteon area ratio differed (p =  0.017) with Type II osteon presence, Type II osteons were more prevalent in males than females (p =  0.048), and drifting osteons were associated with smaller osteon (p =  0.049) and Haversian canal area (p =  0.05). These results may be explained through some biological (sex) and social (status) processes such as a period of physiological recovery (e.g., following lactation, malnutrition). However, the general lack of consistent relationships between osteon variants and remodeling indicators suggests they occur as a result of natural variation.

TGFβ Regulation of Perilacunar/Canalicular Remodeling Is Sexually Dimorphic

Bone fragility is the product of defects in bone mass and bone quality, both of which show sex-specific differences. Despite this, the cellular and molecular mechanisms underpinning the sexually dimorphic control of bone quality remain unclear, limiting our ability to effectively prevent fractures, especially in postmenopausal osteoporosis. Recently, using male mice, we found that systemic or osteocyte-intrinsic inhibition of TGFβ signaling, achieved using the 9.6-kb DMP1 promoter-driven Cre recombinase (TβRII^ocy-/- mice), suppresses osteocyte perilacunar/canalicular remodeling (PLR) and compromises bone quality. Because systemic TGFβ inhibition more robustly increases bone mass in female than male mice, we postulated that sex-specific differences in bone quality could likewise result, in part, from dimorphic regulation of PLR by TGFβ. Moreover, because lactation induces PLR, we examined the effect of TGFβ inhibition on the female skeleton during lactation. In contrast to males, female mice that possess an osteocyte-intrinsic defect in TGFβ signaling were protected from TGFβ-dependent defects in PLR and bone quality. The expression of requisite PLR enzymes, the lacunocanalicular network (LCN), and the flexural strength of female TβRII^ocy-/- bone was intact. With lactation, however, bone loss and induction in PLR and osteocytic parathyroid hormone type I receptor (PTHR1) expression, were suppressed in TβRII^ocy-/- bone, relative to the control littermates. Indeed, differential control of PTHR1 expression, by TGFβ and other factors, may contribute to dimorphism in PLR regulation in male and female TβRII^ocy-/- mice. These findings provide key insights into the sex-based differences in osteocyte PLR that underlie bone quality and highlight TGFβ signaling as a crucial regulator of lactation-induced PLR. © 2020 American Society for Bone and Mineral Research.

Low protein intake during reproduction compromises the recovery of lactation-induced bone loss in female mouse dams without affecting skeletal muscles

Lactation-induced bone loss occurs due to high calcium requirements for fetal growth but skeletal recovery is normally achieved promptly postweaning. Dietary protein is vital for fetus and mother but the effects of protein undernutrition on the maternal skeleton and skeletal muscles are largely unknown. We used mouse dams fed with normal (N, 20%) or low (L, 8%) protein diet during gestation and lactation and maintained on the same diets (NN, LL) or switched from low to normal (LN) during a 28 d skeletal restoration period post lactation. Skeletal muscle morphology and neuromuscular junction integrity was not different between any of the groups. However, dams fed the low protein diet showed extensive bone loss by the end of lactation, followed by full skeletal recovery in NN dams, partial recovery in LN and poor bone recovery in LL dams. Primary osteoblasts from low protein diet fed mice showed decreased in vitro bone formation and decreased osteogenic marker gene expression; promoter methylation analysis by pyrosequencing showed no differences in Bmpr1a, Ptch1, Sirt1, Osx, and Igf1r osteoregulators, while miR-26a, -34a, and -125b expression was found altered in low protein fed mice. Therefore, normal protein diet is indispensable for maternal musculoskeletal health during the reproductive period.

How does women's bone health recover after lactation? A systematic review and meta-analysis

This is a systematic review aiming to evaluate the recovery of bone mass after lactation-related loss. Bone loss is transitory with recovery depending on the return of menstruation and weaning, and several compensatory homeostatic mechanisms are involved to minimize any significant damage to the maternal skeleton. 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 meta-analysis 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.

Glucose dependent miR-451a expression contributes to parathyroid hormone mediated osteoblast differentiation

Parathyroid hormone (PTH; amino acid 1-34, known as teriparatide) has reported promoting differentiation and glucose uptake in osteoblasts. However, how PTH regulates glucose metabolism to facilitate osteoblast differentiation is not understood. Here, we report that PTH promotes glucose dependent miR-451a expression which stimulates osteoblast differentiation. In addition to glucose uptake, PTH suppresses AMPK phosphorylation via PI3K-mTOR-AKT axis thereby preventing phosphorylation and inactivation of octamer-binding transcription factor 1 (OCT-1) which has been reported to act on the promoter region of miR-451a. Modulation of AMPK activity controls miR-451a levels in differentiating osteoblasts. Moreover, pharmacological inhibition of PI3K-mTOR-AKT axis suppressed miR-451a via increased AMPK activity. We report that this glucose regulated miRNA is an anabolic target and transfection of miR-451a mimic induces osteoblast differentiation and mineralization in vitro. These actions were mediated through the suppression of Odd-skipped related 1 (Osr1) and activation of Runx2 transcription. When injected in vivo, the miR-451a mimic significantly increased osteoblastogenesis, mineralization, reversed ovariectomy induced bone loss and improved bone strength. Together, these findings suggest that enhanced osteoblast differentiation associated with bone formation in case of PTH therapy is also a consequence of elevated miR-451a levels via glucose regulation. Consequently, this miRNA has the potential to be a therapeutic target for conditions of bone loss.

Postpartum sacral stress fracture associated with mechanical sacroiliac joint disease: A case report

RATIONALE

Stress fractures of the sacrum and mechanical sacroiliac joint disease can occur not only during pregnancy but also postpartum. Mechanical sacroiliac joint disease is common in patients with low back pain but often misdiagnosed by practitioners. The association of the 2 conditions has not been studied yet.

PATIENT CONCERNS

A 37-year-old woman physiatrist presented with 8-week history of persistent low back and left buttock pain that started in the third trimester of her pregnancy.

DIAGNOSES

Laboratory investigation, dual-energy x-ray absorptiometry, magnetic resonance imaging, and CT of the pelvic region were performed. The patient was diagnosed with postpartum sacral stress fracture associated with mechanical sacroiliac joint disease.

INTERVENTIONS

Treatment consisted in pain killers and tailored to a nonweight-bearing period of 3 months.

OUTCOMES

Painful symptoms disappeared and the patient was able to walk and perform other daily activities normally.

LESSONS

Clinician should be aware of the clinical context and the possible association of these 2 conditions in order to undertake an early and appropriate treatment.

Effects of reproduction on sexual dimorphisms in rat bone mechanics

Osteoporosis most commonly affects postmenopausal women. Although men are also affected, women over 65 are 6 times more likely to develop osteoporosis than men of the same age. This is largely due to accelerated bone remodeling after menopause; however, the peak bone mass attained during young adulthood also plays an important role in osteoporosis risk. Multiple studies have demonstrated sexual dimorphisms in peak bone mass, and additionally, the female skeleton is significantly altered during pregnancy/lactation. Although clinical studies suggest that a reproductive history does not increase the risk of developing postmenopausal osteoporosis, reproduction has been shown to induce long-lasting alterations in maternal bone structure and mechanics, and the effects of pregnancy and lactation on maternal peak bone quality are not well understood. This study compared the structural and mechanical properties of male, virgin female, and post-reproductive female rat bone at multiple skeletal sites and at three different ages. We found that virgin females had a larger quantity of trabecular bone with greater trabecular number and more plate-like morphology, and, relative to their body weight, had a greater cortical bone size and greater bone strength than males. Post-reproductive females had altered trabecular microarchitecture relative to virgins, which was highly similar to that of male rats, and showed similar cortical bone size and bone mechanics to virgin females. This suggests that, to compensate for future reproductive bone losses, females may start off with more trabecular bone than is mechanically necessary, which may explain the paradox that reproduction induces long-lasting changes in maternal bone without increasing postmenopausal fracture risk.

Reproduction Differentially Affects Trabecular Bone Depending on Its Mechanical Versus Metabolic Role

During pregnancy and lactation, the maternal skeleton provides calcium for fetal/infant growth, resulting in substantial bone loss, which partially recovers after weaning. However, the amount of bone that is lost and the extent of post-weaning recovery are highly variable among different skeletal sites, and, despite persistent alterations in bone structure at some locations, reproductive history does not increase postmenopausal fracture risk. To explain this phenomenon, we hypothesized that the degree of reproductive bone loss/recovery at trabecular sites may vary depending on the extent to which the trabecular compartment is involved in the bone's load-bearing function. Using a rat model, we quantified the proportion of the load carried by the trabeculae, as well as the extent of reproductive bone loss and recovery, at two distinct skeletal sites: the tibia and lumbar vertebra. Both sites underwent significant bone loss during pregnancy and lactation, which was partially recovered post-weaning. However, the extent of the deterioration and the resumption of trabecular load-bearing capacity after weaning varied substantially. Tibial trabecular bone, which bore a low proportion of the total applied load, underwent dramatic and irreversible microstructural deterioration during reproduction. Meanwhile, vertebral trabecular bone bore a greater fraction of the load, underwent minimal deterioration in microarchitecture, and resumed its full load-bearing capacity after weaning. Because pregnancy and lactation are physiological processes, the distinctive responses to these natural events among different skeletal sites may help to elucidate the extent of the trabecular bone's structural versus metabolic functions.

Quality in dual-energy X-ray absorptiometry scans

Dual-energy X-ray absorptiometry (DXA) is the gold standard for measuring bone mineral density (BMD), making the diagnosis of osteoporosis, and for monitoring changes in BMD over time. DXA data are also used in the determination of fracture risk. Procedural steps in DXA scanning can be broken down into scan acquisition, analysis, interpretation, and reporting. Careful attention to quality control pertaining to these procedural steps should theoretically be beneficial in patient management. Inattention to procedural steps and errors that may occur at each step has the possibility of providing information that would inform inappropriate clinical decisions, generating unnecessary healthcare expenses and ultimately causing avoidable harm to patients. This article reviews errors in DXA scanning that affect trueness and precision related to the machine, the patient, and the technologist and reviews articles which document problems with DXA quality in clinical and research settings. An understanding of DXA errors is critical for DXA quality; programs such as certification of DXA technologists and interpreters help in assuring quality bone densitometry. As DXA errors are common, pay for performance requiring DXA technologists and interpreters to be certified and follow quality indicators is indicated.

Adaptations in the Microarchitecture and Load Distribution of Maternal Cortical and Trabecular Bone in Response to Multiple Reproductive Cycles in Rats

Pregnancy, lactation, and weaning result in dramatic changes in maternal calcium metabolism. In particular, the increased calcium demand during lactation causes a substantial degree of maternal bone loss. This reproductive bone loss has been suggested to be largely reversible, as multiple clinical studies have found that parity and lactation history have no adverse effect on postmenopausal fracture risk. However, the precise effects of pregnancy, lactation, and post-weaning recovery on maternal bone structure are not well understood. Our study aimed to address this question by longitudinally tracking changes in trabecular and cortical bone microarchitecture at the proximal tibia in rats throughout three cycles of pregnancy, lactation, and post-weaning using in vivo μCT. We found that the trabecular thickness underwent a reversible deterioration during pregnancy and lactation, which was fully recovered after weaning, whereas other parameters of trabecular microarchitecture (including trabecular number, spacing, connectivity density, and structure model index) underwent a more permanent deterioration, which recovered minimally. Thus, pregnancy and lactation resulted in both transient and long-lasting alterations in trabecular microstructure. In the meantime, multiple reproductive cycles appeared to improve the robustness of cortical bone (resulting in an elevated cortical area and polar moment of inertia), as well as increase the proportion of the total load carried by the cortical bone at the proximal tibia. Taken together, changes in the cortical and trabecular compartments suggest that whereas rat tibial trabecular bone appears to be highly involved in maintaining calcium homeostasis during female reproduction, cortical bone adapts to increase its load-bearing capacity, allowing the overall mechanical function of the tibia to be maintained. © 2017 American Society for Bone and Mineral Research.

Parathyroid Hormone-Related Protein, Its Regulation of Cartilage and Bone Development, and Role in Treating Bone Diseases

Although parathyroid hormone-related protein (PTHrP) was discovered as a cancer-derived hormone, it has been revealed as an important paracrine/autocrine regulator in many tissues, where its effects are context dependent. Thus its location and action in the vasculature explained decades-long observations that injection of PTH into animals rapidly lowered blood pressure by producing vasodilatation. Its roles have been specified in development and maturity in cartilage and bone as a crucial regulator of endochondral bone formation and bone remodeling, respectively. Although it shares actions with parathyroid hormone (PTH) through the use of their common receptor, PTHR1, PTHrP has other actions mediated by regions within the molecule beyond the amino-terminal sequence that resembles PTH, including the ability to promote placental transfer of calcium from mother to fetus. A striking feature of the physiology of PTHrP is that it possesses structural features that equip it to be transported in and out of the nucleus, and makes use of a specific nuclear import mechanism to do so. Evidence from mouse genetic experiments shows that PTHrP generated locally in bone is essential for normal bone remodeling. Whereas the main physiological function of PTH is the hormonal regulation of calcium metabolism, locally generated PTHrP is the important physiological mediator of bone remodeling postnatally. Thus the use of intermittent injection of PTH as an anabolic therapy for bone appears to be a pharmacological application of the physiological function of PTHrP. There is much current interest in the possibility of developing PTHrP analogs that might enhance the therapeutic anabolic effects.

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.

Vitamin D expenditure is not altered in pregnancy and lactation despite changes in vitamin D metabolite concentrations

Pregnancy and lactation are associated with changes in vitamin D and calcium metabolism but the impact of these changes on vitamin D expenditure is unknown. We measured plasma 25(OH)D₃ half-life with a stable-isotope tracer and investigated relationships with vitamin D metabolites in pregnant, lactating and ‘non-pregnant, non-lactating’ (NPNL) women. Vitamin D metabolites, vitamin D binding protein (DBP), PTH and 25(OH)D₃ half-life were measured in third-trimester pregnant women (n22) and repeated during lactation 12 weeks post-partum (n14) and twice in NPNL women (n23 and n10, respectively) in rural Gambia where calcium intakes are low with little seasonality in UVB-exposure. 25(OH)D₃ half-life was not significantly different between groups (mean(SD): 20.6(6.8), 22.6(7.7), 18.0(4.7) and 17.7(9.5) days in pregnant, lactating and NPNL women, respectively). Plasma 25(OH)D₃, 1,25(OH)₂D, and DBP were higher in pregnancy, and calculated free-25(OH)D₃ and PTH were lower (P < 0.05). In lactation, 25(OH)D₃ and 24,25(OH)₂D₃ were lower compared to pregnant (P < 0.001, P = 0.02) and NPNL women (P = 0.04, P = 0.07). Significant associations were observed between half-life and 25(OH)D₃ (+ve) in pregnancy, and in all groups between 25(OH)D₃ and free-25(OH)D₃ (+ve) and PTH and 25(OH)D₃ (−ve) (P < 0.0001). These data suggest that adaptive changes in pregnancy and lactation occur that prevent pronounced changes in vitamin D expenditure.

Association Between Recurrence of Urinary Calculi and Childbirth: A Population-Based Case-Control Study

We examined the recurrence rate of urinary calculi (UC) in women after childbirth. The recurrence of UC is common, but no previous studies mentioned the risk of recurrence after childbirth. We performed a nationwide population-based cohort study to investigate whether childbirth could correlate with the recurrence of UC by using data from the National Health Insurance Research Database in Taiwan. Nulliparous women (age ≥20 years) receiving a diagnosis of first episode of UC between 2000 and 2002 were enrolled. We recorded the events of recurrence between parous patients (n = 737) and matched-control nulliparous patients (n = 737). The average ages for parous patients and controls were 27.41 and 27.54, respectively. The recurrence rate was 11.67% (86 of 737) in the childbirth cohort group and 21.57% (159 of 737) in the nonchildbirth cohort group. The childbirth cohort group was associated with a significantly decreased risk of secondary UC (adjusted hazard ratio, 0.45; 95% confidence interval, 0.35–0.59) compared with those who did not deliver a child. This relationship should be studied further.

Novel anatomic adaptation of cortical bone to meet increased mineral demands of reproduction

The goal of this study was to investigate the effects of reproductive adaptations to mineral homeostasis on the skeleton in a mouse model of compromised mineral homeostasis compared to adaptations in control, unaffected mice. During pregnancy, maternal adaptations to high mineral demand include more than doubling intestinal calcium absorption by increasing calcitriol production. However, calcitriol biosynthesis is impaired in HYP mice, a murine model of X-linked hypophosphatemia (XLH). In addition, there is a paucity of mineralized trabecular bone, a primary target of bone resorption during pregnancy and lactation. Because the highest density of mineral is in mature cortical bone, we hypothesized that mineral demand is met by utilizing intracortical mineral reserves. Indeed, analysis of HYP mice revealed dramatic increases in intracortical porosity characterized by elevated serum PTH and type-I collagen matrix-degrading enzyme MMP-13. We discovered an increase in carbonate ion substitution in the bone mineral matrix during pregnancy and lactation of HYP mice, suggesting an alternative mechanism of bone remodeling that maintains maternal bone mass during periods of high mineral demand. This phenomenon is not restricted to XLH, as increased carbonate in the mineral matrix also occurred in wild-type mice during lactation. Taken together, these data suggest that increased intracortical perilacunar mineral turnover also contributes to maintaining phosphate levels during periods of high mineral demand. Understanding the mechanisms of skeletal contribution to mineral homeostasis is important to improving the treatment and prevention of fracture risk and bone fragility for female patients with XLH, but also provides important insight into the role and unique adaptations of the maternal skeleton to the demands of fetal development and the needs of postnatal nutrition.

Parity, lactation, bone strength, and 16-year fracture risk in adult women: findings from the Study of Women's Health Across the Nation (SWAN)

Our objective was to examine the associations of lifetime parity and accumulated length of lactation with bone strength in women prior to the menopause transition and fracture risk during and after the transition. Participants were 2239 pre- or early peri-menopausal women from the Study of Women's Health Across the Nation (SWAN), ages 42-53 years at baseline, who had no childbirths after age 42. Bone mineral density (BMD) was measured in the femoral neck and the lumbar spine at the baseline SWAN visit using dual-energy x-ray absorptiometry, and the composite indices of femoral neck strength relative to load (in three failure modes: compression, bending, and impact) were calculated from femoral neck BMD, femoral neck size, and body size. Data on fractures after age 42 were collected for a median follow-up of 15.7 years (interquartile range, 11.4-18.5 years). In multiple linear regressions adjusted for covariates, lifetime parity was associated positively with femoral neck strength relative to load (0.024 standard deviation (SD) increment in impact strength index per childbirth, p=0.049), but accumulated length of lactation was associated negatively with lumbar spine BMD (0.018 SD decrement per every additional 6 months of lactation, p=0.040). In Cox proportional hazards regressions adjusted for covariates, neither parity nor lactation was associated with fracture hazard after age 42. In conclusion, parity and lactation have little impact on peak bone strength prior to menopause, and do not affect fracture risk after age 42 over 16-year follow-up.

Quantitative ultrasonometry during pregnancy and lactation: a longitudinal study

This study describes bone mass changes during pregnancy and lactation measured by a special ultrasound method. Pregnant women showed a decrease of bone mass followed by a stable bone mass while breast-feeding afterwards. Later in life, there is a recovery of bone mass loss.

INTRODUCTION

The aim of this study was to evaluate bone changes during pregnancy using the radiation-free method of quantitative ultrasonometry (QUS).

METHODS

One hundred twenty-five pregnant women who underwent prenatal care were included in this study. Ultrasound measurement of the calcaneus was performed in each trimester and then 6 weeks, 3 months, and 1 year postpartum. The calcaneal QUS measurements were carried out using the Achilles plus device (GE/Lunar Corporation, Madison, WI). Three ultrasound variables were measured: speed of sound (SOS, m/s), broadband ultrasound attenuation (BUA, dB/MHz), and the "stiffness index" (expressed as the percentage of the mean value in young adults). SOS and BUA raw data result in the t-score and z-score.

RESULTS

A complete panel of six measurements was acquired over the time period in 101 patients (80.8%). Forty-two percent of the included patients were primipara, while 58% had given birth to at least one child (47%) previously. There was a statistically significant change of the t-score (tv = 2.14, p = 0.035) and the stiffness index (tv = 2.46, p = 0.016) from the second to the third trimester, followed by a plateau during lactation. Interestingly, the t-score remained stable during lactation, regardless of the duration of lactation (<3 months, 3-6 months, and >6 months).

CONCLUSIONS

Young primiparas who had a sedentary adolescence were at the highest risk of bone loss during pregnancy. Bone loss that occurred during pregnancy was typically recovered later on, based on unknown molecular and biochemical mechanisms that must be elucidated with further studies.

Physiological skeletal gains and losses in rat mothers during pregnancy and lactation are not observed following uteroplacental insufficiency

Fluctuations in maternal bone mass during pregnancy and lactation facilitate calcium transfer to offspring. Uteroplacental insufficiency causes fetal growth restriction and programs poor adult bone health. We aimed to characterise maternal skeletal phenotype during normal pregnancy and pregnancy complicated by uteroplacental insufficiency. Uteroplacental restriction (Restricted) or sham surgery (Control) was performed on gestational Day 18 (term=22 days) in pregnant Wistar-Kyoto rats. Maternal right femurs were collected on embryonic Day 20, postnatal Day 1 and Weeks 5, 7 and 9 postnatal. Dual-energy X-ray absorptiometry was used to quantify global bone mineral content, density and body composition. Peripheral quantitative computed tomography was utilised to determine trabecular and cortical content, density, circumferences and strength. Control rats exhibited expected reductions in trabecular and cortical content, density and bone strength from embryonic Day 20 to postnatal Day 1 (P<0.05). These skeletal alterations were absent in Restricted rats. By postnatal Day 7, bone parameters in Control and Restricted rats were not different from non-pregnant rats, indicating restoration of maternal bone. The lack of bone loss in mothers suffering uteroplacental insufficiency suggests that calcium transfer to pups would be impaired. This reduction in calcium availability is a likely contributor to the programming of poor adult bone health in growth-restricted offspring.

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.

Transient peripartum osteoporosis of the femoral head in first and third pregnancy

The aim of this article was to present transient peripartum femoral head osteoporosis. This very rare condition occurred twice in our patient-a woman in her 30s. The cases described in the literature were mostly unilateral, with bilateral hip involvement noted much less frequently. In our patient, transient osteoporosis occurred in the third trimester of her first pregnancy in the right hip, her second pregnancy was uncomplicated, and in the third trimester of the patient's third pregnancy, osteoporotic changes were noted in the left hip joint. The patient breastfed her first and third babies only 3 wk each. She breastfed her second baby for 4 mo. The diagnostic workup was based on the clinical examination and radiographic/magnetic resonance imaging, which revealed bone marrow edema, and the dual-energy X-ray absorptiometry scans. The treatment consisted in core decompression of the femoral head (foragé), unloading of the hip using crutches as well as administration of calcitonin and calcium supplements. Complete recovery of the femoral heads was achieved. The follow-up time was 7 yr.

Site-specific changes in bone microarchitecture, mineralization, and stiffness during lactation and after weaning in mice

Despite the dramatic bone loss that occurs during lactation, bone mineral density rapidly recovers after offspring are weaned and milk production stops. The goal of this study is to quantify site-specific changes in bone quantity and quality during and after lactation in a mouse model. We used micro computed tomography (µCT), individual trabecula segmentation (ITS), digital topological analysis (DTA)-based tissue mineral density (TMD) analysis, and micro finite element analysis (µFEA) to quantify the effects of lactation and weaning on bone microarchitecture, mineralization, and stiffness at the spine, tibia, and femur. We found a significant decrease in trabecular plate microarchitecture, tissue mineralization of the trabecular surface, trabecular central skeleton, and intervening envelopes, and whole bone stiffness in lactating versus nulliparous mice at all three sites. In recovered mice, all these different aspects of bone quality were comparable to nulliparous mice at the spine. In contrast, trabecular plate microarchitecture and whole bone stiffness at the tibia and femur in recovered mice were lower than nulliparous mice, as were central trabecular tissue mineralization and cortical structure at the femur. These findings are consistent with clinical observations of partial recovery of femoral bone mineral density BMD after lactation in humans. The observed differences in trabecular surface tissue mineralization in nulliparous, lactating, and recovered mice are consistent with prior observations that maternal bone turnover shifts from resorption to formation at the time of pup weaning. The significant differences in trabecular central tissue mineralization during these three states suggest that osteocytes may contribute to the reversible loss of mineral during and after lactation. Future studies are necessary to determine whether differing functions of various bone cells at individual skeletal sites cause site-specific skeletal changes during and after lactation.

Effects of 25OHD concentrations on chances of pregnancy and pregnancy outcomes: a cohort study in healthy Danish women

BACKGROUND/OBJECTIVES

Plasma 25-hydroxyvitamin D (P-25OHD) concentrations may affect pregnancy outcomes. To elucidate this further, we studied the effects of pre-conception P-25OHD concentrations on chances for pregnancy as well as the effects of P-25OHD during pregnancy on the risk of miscarriage, birth weight and length, Apgar score and head circumference. Moreover, we studied whether pregnancy and breastfeeding patterns affect maternal P-25OHD concentrations.

SUBJECTS/METHODS

A total of 153 healthy Caucasian women with pregnancy plans were followed with measurements performed before pregnancy, at pregnancy weeks 11±2, 22±1 and 35±2 as well as 15±7, 129±12 and 280±15 days postpartum. Furthermore, 75 non-pregnant, age-matched women were followed in parallel as controls.

RESULTS

The 203 women were aged 29 (25-35) years. At baseline, median P-25OHD was 59 nmol/l. Of these women, 31% had P-25OHD <50 nmol/l, whereas 12% had levels above 80 nmol/l. Within ∼6 months after inclusion, 63% conceived. P-25OHD was not associated with chances of conceiving or overall risk of miscarriage. However, women with a miscarriage in their second trimester (n=3) had lower P-25OHD concentrations at measurements performed in the first trimester compared with women without a miscarriage (P=0.03). P-25OHD before or during pregnancy was not associated with gestational length or infant parameters. Adjustments for possible confounders did not change the result. During pregnancy, P-25OHD changed significant over time, but similar changes occurred within the control group, indicating no effect of pregnancy per se (P=0.59). Overall, P-25OHD did not differ according to length of breastfeeding at 2 weeks, and 4 and 9 months postpartum, although women breastfeeding for >9 months had lower P-25OHD levels at the last visit compared with the controls.

CONCLUSION

P-25OHD concentrations did not affect fertility or pregnancy outcomes, although low P-25OHD may be associated with an increased risk of late miscarriage.

Skeletal indicators of pregnancy and parturition: a historical review

Over a century of scientific literature has documented the research and analysis relating to the possible skeletal evidence of pregnancy, parturition, and childcare, yet today, there still exists variation in methodology and interpretation. Historical perspective facilitates understanding of the growth and development of the theories and research currently available to the forensic science community. Review of the relevant literature clearly indicates that specific skeletal alterations are not exclusively connected to obstetrical events. Although parturition and related events have been shown to leave various alterations on bone, the research record also demonstrates that other factors can contribute to the same or similar changes. Additionally, such alterations can often be found in nulliparous women and men and are frequently absent in parous and multiparous women. This literature review calls for the continued exploration of skeletal alterations for determining parity status in human skeletal remains.

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.

Primary hyperparathyroidism in pregnancy-a rare cause of life-threatening hypercalcemia: case report and literature review

Objective. To report a case of primary hyperparathyroidism in a pregnant patient, report the obstetric and neonatal outcomes, and review the relevant literature. Results. A 29-year-old primigravida was successfully treated for PHP with minimally invasive resection of a parathyroid adenoma in the second trimester of pregnancy. A healthy baby girl was delivered at 37-week gestation with an unremarkable neonatal course. To the best of our knowledge, this is the second case report in the literature utilizing intraoperative PTH during a parathyroidectomy in a pregnant woman. Conclusions. Primary hyperparathyroidism is a rare life-threatening condition that can present during pregnancy. The diagnosis can be difficult to establish during pregnancy, given the nonspecific symptoms related to hypercalcemia. However, a better understanding of the condition, improved diagnostic studies, and well-organized multidisciplinary management decisions can significantly reduce the morbidity and mortality associated with the disease during pregnancy. This case report is presented to highlight the value of early diagnosis and appropriate management of PHP during pregnancy.

Effect of number of pregnancies on bone mineral density

This study investigated the effect of the number of pregnancies on bone mineral density (BMD) in 320 post-menopausal women aged between 49 and 64 years. Cases were selected from people with similar lifestyles and stratified into five groups according to the number of pregnancies. Each group was divided into two subgroups according to the duration of the menopause (3-5 years versus 6-10 years). Lumbar (L2-L4) and femoral neck BMD were measured by dual-energy X-ray absorptiometry and T-score values were used in the statistical evaluation. No significant difference was found between the number of pregnancies and BMD within each group based on the same menopause duration, but a significant correlation was found in most groups based on menopause duration: T-scores decreased as menopause duration increased. Changes in BMD are likely to be related to menopause duration, rather than the number of pregnancies.

Health effects of breast feeding for mothers: a critical review

Lactation results in a number of physiological adaptations which exert direct effects on maternal health, some of which may confer both short and long term advantages for breast feeding mothers. Breast feeding in the early postpartum period promotes a more rapid return of the uterus to its prepregnant state through the actions of oxytocin. Breast feeding may also lead to a more rapid return to prepregnancy weight. Among studies that had good data on duration and intensity of lactation, the majority show a significant association between lactation and weight loss. However, there is no evidence that lactation prevents obesity. Lactation also affects glucose and lipid metabolism. The long term effects of these adaptations are unknown but may have implications for preventing subsequent development of diabetes and heart disease. Lactation delays the return of ovulation and significantly reduces fertility during the period of lactational amenorrhoea. This process is linked with feeding patterns and may therefore be affected by practices such as scheduled feedings and the timing of introduction of complementary foods. While the evidence from epidemiologic studies is mixed, several large studies have shown that extended lactation is associated with reduced risk of premenopausal breast, ovarian and endometrial cancers. Although bone mineralization declines during lactation, repletion takes place after weaning. As a result, breast feeding does not appear to cause long term depletion of bone nor does it increase risk of osteoporosis. Many of the physiological effects of lactation are dependent on the stimulation of the hypothalamic-pituitary axis and milk removal and thus may vary with infant feeding practices. Well controlled studies are needed that include detailed information regarding infant feeding practices in addition to the total duration of any breast feeding. Future feeding recommendations should reflect careful consideration of how such practices affect both infant and maternal health.

Quantitative ultrasonometry of the phalanges during pregnancy: a longitudinal study

OBJECTIVE

The aim of this study was to determine prospectively the change in results of bone ultrasonometry measurement during pregnancy in healthy German women. Study design Quantitative ultrasonometry (QUS) of the phalanges was performed in 60 healthy, pregnant women. Measurements of amplitude-dependent bone propagation velocity (speed of sound; AdSOS) and the bone transmission time (BTT) were performed during the three trimesters of pregnancy in 60 patients.

RESULTS

During pregnancy, a significant increase in body weight and body mass index (p < or = 0.001) were observed. In accordance with bone ultrasonometry, a significant reduction in AdSOS was found in each trimester; AdSOS was significantly lower in the second and third trimesters compared with the first (p < or = 0.001). The BTT values also decreased significantly in the second and third trimesters compared with the first (p < or = 0.001). No significant influence was found of possible risk factors such as family risk of osteoporosis, previous pregnancies, age at menarche and prior use of oral contraceptives on QUS measurement results.

CONCLUSIONS

During normal pregnancy, we found a significant reduction of quantitative ultrasonometry variables AdSOS and BTT in healthy pregnant women. This decrease had a large influence on the t score and Z score of QUS in our study and demonstrates therefore a possible clinical relevance. The decrease was independent of osteoporosis-related risk factors and the increase in body weight. More large-scale, prospective studies are needed to increase our knowledge about the mechanism of bone turnover during pregnancy and lactation.

Calcium metabolism in pregnancy and lactation

Homeostatic adaptation to maternal calcium metabolism is a prerequisite for optimal delivery of sufficient calcium to the fetus and neonate during pregnancy and lactation, respectively. This article outlines the major adaptations known to occur and the physiological regulators likely to be principally involved. Importantly, different adaptive responses are used in pregnancy and lactation. The rarity of calcium disorders in pregnancy underscores the successful implementation of these adaptations in most women. For those few women with either pre-existing or pregnancy-acquired disorders of calcium metabolism, a knowledge of normal physiology is essential to understand the implications for managing these disorders in pregnant women.

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.

Bone growth and turnover in progesterone receptor knockout mice

The role of progesterone receptor (PR) signaling in skeletal metabolism is controversial. To address whether signaling through the PR is necessary for normal bone growth and turnover, we performed histomorphometric and microcomputed tomography analyses of bone from homozygous female PR knockout (PRKO) mice at 6, 12, and 26 wk of age. These mice possess a null mutation of the PR locus, which blocks the gene expression of A and B isoforms of PR. Body weight gain, uterine weight gain, and tibia longitudinal bone growth were normal in PRKO mice. In contrast, total, cancellous, and cortical bone mass were increased in the humerus of 12-wk-old PRKO mice, whereas cortical and cancellous bone mass in the tibia was normal. At 26 wk of age, cancellous bone area in the proximal tibia metaphysis of PRKO mice was 153% greater than age matched wild-type mice. The improved cancellous bone balance in 6-month-old PRKO mice was associated with elevated bone formation and a tendency toward reduced osteoclast perimeter. Taken together, these findings suggest that PR signaling in mice is not essential for bone growth and turnover. However, at some skeletal sites, PR signaling attenuates the accumulation of cortical and cancellous bone mass during adolescence.

Rapid inactivation and apoptosis of osteoclasts in the maternal skeleton during the bone remodeling reversal at the end of lactation

There is a rapid reversal in maternal skeletal metabolism and bone remodeling from accelerated bone resorption during lactation to skeletal rebuilding after lactation. The purpose was to determine the changes that occur in maternal osteoclasts during the transition from lactation to postlactation. Skeletal samples were taken from female rats on days 10 and 19 of lactation and 1 and 7 days after lactation. The pups were weaned on day 20. There was a rapid change in the osteoclast population after weaning, resulting in less resorption surface. Osteoclasts detached from bone surfaces, lost their ruffled borders, and became fragmented with immunocytochemical evidence of apoptosis within 24 hr after lactation. Concomitant with the rapid regression in the osteoclast population was an over fivefold increase in maternal calcitonin (CT) levels at 24 hr after weaning. Serum calcium and estrogen (E2) increased, but prolactin (PRL) and PTH decreased after weaning. The hormone changes, particularly that of CT, are consistent with the rapid regression of the osteoclast population at the end of lactation. These changes are similar to a reversal phase of a bone remodeling cycle where bone formation commences when resorption ceases on bone surfaces and suggests that the fate of osteoclasts during bone remodeling is programmed cell death. These results also suggest that bone remodeling is well synchronized prior to, during, and after lactation to accommodate the mineral requirements of the offspring as well as the mother.

Sacral insufficiency fractures: current concepts of management

BACKGROUND

Sacral insufficiency fractures (SIFs) are often overlooked in elderly patients presenting with low back and pelvic pain following no or minimal trauma.

OBJECTIVE

The aim of this review is to raise awareness and outline the clinical presentation, methods of diagnosis and treatment of SIFs.

DISCUSSION

Insufficiency fractures represent a special category of stress fractures that occur in bones with reduced mineral content and elastic resistance. SIFs, a well-defined subgroup of the latter group, are not uncommon, but lack of clinical suspicion results in many being undiagnosed. SIFs are set to become an important clinical entity of both social and economic significance as the Western population ages. Subtle clinical presentations and signs coupled with radiographic findings that can mimic other unrelated or overlapping conditions, such as sacroiliac joint infection, spinal stenosis and metastatic bone disease, often make SIF diagnosis a challenge. The aim of this review is to increase awareness among clinicians, highlighting SIFs as an important differential diagnosis to be considered when patients present with low back and pelvic pain and subsequently allow prompt management. The paper provides an overview of epidemiology, anatomical considerations, relevant pathophysiology and risk factors, presenting symptoms and signs, investigations and imaging techniques, differential diagnoses and current treatment methods available for the management of SIFs.

Bone status during adolescence, pregnancy and lactation

PURPOSE OF REVIEW

At birth, the fetus will contain 30 g of calcium; during the third trimester the calcium accrual can be up to 340 mg/day. Therefore, extremely high demands for calcium provision are placed upon the mother. This review aims to describe the adaptive mechanisms of the female skeleton to pregnancy and lactation, which ensure optimal fetal skeletal mineralization without compromise to maternal bone strength.

RECENT FINDINGS

Descriptions of changes in bone status during pregnancy and lactation have been published. One of the only studies to measure pre-conception to post-weaning shows complete recovery of maternal spinal bone mineral density (BMD) and near recovery at the hip. Most studies describe trabecular bone loss, but there is evidence for endosteal resorption of the metacarpals. In a retrospective study of former teenage mothers those who breastfed had similar hip BMD to nulliparous age-matched women; those who did not breastfeed had lower hip BMD. Maternal response to low calcium intake differs from that of normal calcium intake.

SUMMARY

Pregnancy and lactation do not have an overall negative effect upon the maternal skeleton. Retrospective evidence suggests no harmful effect of teenage pregnancy if the teenager breastfed, but this requires further investigation. The effects of other situations, for example low vitamin D status or low calcium intake, require further research to inform future clinical practice.

Sacral stress fractures

Sacral stress fractures are a relatively common occurrence and can be a debilitating source of low back pain. They generally occur in two distinctly different patient populations, and are of two different etiologies. Sacral insufficiency-type fractures are seen in elderly osteoporotic persons, and fatigue fractures are seen young active individuals. Although the clinical presentation of these fractures is similar, medical rehabilitation and interventional spine management strategies differ according to etiology. Although conservative management strategies have resulted in good outcomes, other treatment options have recently developed. This article provides an overview of the clinical presentation, pathology, and treatment options for sacral stress fractures and discusses some of the recent literature surrounding this interesting topic.