Catch up in bone acquisition in young adult men with late normal puberty

Normalization of puberty and adult height in girls with Turner syndrome: results of the Swedish Growth Hormone trials initiating transition into adulthood

Objective

To study the impact of GH dose and age at GH start in girls with Turner syndrome (TS), aiming for normal height and age at pubertal onset (PO) and at adult height (AH). However, age at diagnosis will limit treatment possibilities.

Methods

National multicenter investigator-initiated studies (TNR 87-052-01 and TNR 88-072) in girls with TS, age 3-16 years at GH start during year 1987-1998, with AH in 2003-2011. Of the 144 prepubertal girls with TS, 132 girls were followed to AH (intention to treat), while 43 girls reduced dose or stopped treatment prematurely, making n=89 for Per Protocol population. Age at GH start was 3-9 years (young; n=79) or 9-16 years (old; n=53). Treatment given were recombinant human (rh)GH (Genotropin^® Kabi Peptide Hormones, Sweden) 33 or 67 µg/kg/day, oral ethinyl-estradiol (2/3) or transdermal 17β-estradiol (1/3), and, after age 11 years, mostly oxandrolone. Gain in height_SDS, AH_SDS, and age at PO and at AH were evaluated.

Results

At GH start, height_SDS was -2.8 (versus non-TS girls) for all subgroups and mean age for young was 5.7 years and that of old was 11.6 years. There was a clear dose-response in both young and old TS girls; the mean difference was (95%CI) 0.66 (-0.91 to -0.26) and 0.57 (-1.0 to -0.13), respectively. The prepubertal gain_SDS (1.3-2.1) was partly lost during puberty (-0.4 to -2.1). Age/height_SDS at PO ranged from 13 years/-0.42 for GH_67young to 15.2 years/-1.47 for GH_33old. At AH, GH_67old group became tallest (17.2 years; 159.9 cm; -1.27 SDS; total gain_SDS, 1.55) compared to GH_67young group being least delayed (16.1 years; 157.1 cm; -1.73 SDS; total, 1.08). The shortest was the GH_33young group (17.3 years; 153.7 cm: -2.28 SDS; total gain_SDS, 0.53), and the most delayed was the GH_33old group, (18.5 years; 156.5 cm; -1.82 SDS; total gain_SDS, 0.98).

Conclusion

For both young and old TS girls, there was a GH-dose growth response, and for the young, there was less delayed age at PO and at AH. All four groups reached an AH within normal range, despite partly losing the prepubertal gain during puberty. Depending on age at diagnosis, low age at start with higher GH dose resulted in greater prepubertal height gain, permitting estrogen to start earlier at normal age and attaining normal AH at normal age, favoring physiological treatment and possibly also bone health, hearing, uterine growth and fertility, psychosocial wellbeing during adolescence, and the transition to adulthood.

Exposure to famine in every stage of life and the risk of osteoporosis and fractures later in life: A cross-sectional study

BACKGROUND AND OBJECTIVE

Data on the association between early-life famine exposure and osteoporosis and fractures remain limited and inconclusive. The aim of this study was to investigate the correlation between famine exposure and osteoporosis and fractures.

METHODS

We performed a cross-sectional analysis using the first follow-up survey data from the China Cardiometabolic Disease and Cancer Cohort Study from 2014 to 2016. We classified 4807 Lanzhou participants into seven groups based on their birthday (non-exposed or exposed in the fetal stage, early childhood, mid-childhood, late childhood, adolescence, or early adulthood). And we combined the non-exposed and early-adulthood exposed groups as a control group, which was called "age balanced group". This age-balanced group was used as the control group to further evaluate the risk of osteoporosis and fracture. We used multiple logistic regression to estimate the association between famine exposure and the risk of osteoporosis (T-score ≤ -1.8 by QUS) and self-reported fracture.

RESULTS

In women, compared to the age-balanced group, the odds ratios (95 % CI) for the risk of osteoporosis were 1.400(1.034, 1.897), 1.630(1.268, 2.095), 1.707(1.314, 2.218), 2.150(1.732.2.668) and 2.885(2.286,3.641) in the fetal stage, early childhood, mid-childhood, late childhood and adolescence famine-exposed cohorts. In men, no association between famine and osteoporosis was noted with exposed cohort compared with the age-balanced control cohort (p > 0.05). Interestingly, the association between famine exposure and fractures was slightly different from the above results: in women, the odds ratios (95 % CI) for fractures in mid-childhood famine exposure was 1.461(1.082,1.973), in late childhood famine exposure was 1.333(1.035,1.718) and in adolescence famine exposure was 1.607(1.239,2.085). However, compared to the age-balanced control cohort, men exposed to famine in early childhood (OR: 1.801, 95 % CI: 1.010,3.211) had a higher risk of fracture.

CONCLUSION

Famine exposure in different life stage has adverse effects on bone health. Famine exposure in not only the period from gestation to infancy, but also childhood and adolescence was associated with an increased risk of osteoporosis, especially in women. Exposure to famine in childhood- (mid and late) and adolescence- life period is associated with fracture in women. But, in men early-childhood famine exposure was only associated with fracture.

Impact of gender-affirming treatment on bone health in transgender and gender diverse youth

Both in the United States and Europe, the number of minors who present at transgender healthcare services before the onset of puberty is rapidly expanding. Many of those who will have persistent gender dysphoria at the onset of puberty will pursue long-term puberty suppression before reaching the appropriate age to start using gender-affirming hormones. Exposure to pubertal sex steroids is thus significantly deferred in these individuals. Puberty is a critical period for bone development: increasing concentrations of estrogens and androgens (directly or after aromatization to estrogens) promote progressive bone growth and mineralization and induce sexually dimorphic skeletal changes. As a consequence, safety concerns regarding bone development and increased future fracture risk in transgender youth have been raised. We here review published data on bone development in transgender adolescents, focusing in particular on differences in age and pubertal stage at the start of puberty suppression, chosen strategy to block puberty progression, duration of puberty suppression, and the timing of re-evaluation after estradiol or testosterone administration. Results consistently indicate a negative impact of long-term puberty suppression on bone mineral density, especially at the lumbar spine, which is only partially restored after sex steroid administration. Trans girls are more vulnerable than trans boys for compromised bone health. Behavioral health measures that can promote bone mineralization, such as weight-bearing exercise and calcium and vitamin D supplementation, are strongly recommended in transgender youth, during the phase of puberty suppression and thereafter.

Age at attainment of peak bone mineral density and its associated factors: The National Health and Nutrition Examination Survey 2005-2014

Osteoporosis is a major public health problem worldwide. Lower peak bone mineral density (BMD) in youth may be the single most important factor leading to the development of osteoporosis in the elderly. Using cross-sectional data from the National Health and Nutrition Examination Survey (NHANES) 2005-2014, we included 18,713 individuals with complete and valid data on femoral neck, total hip and lumbar spine BMD. Generalized additive models were used to estimate the age at attainment of peak BMD and 95% confidence intervals (95%Cls); model covariates were sex, race, body mass index (BMI) and we also examine factors potentially affecting age at attainment of peak BMD. This study clearly stated that age at attainment of peak femoral neck, total hip and lumbar spine BMD were 20.5 years, 21.2 years and 23.6 years in males, and 18.7 years, 19.0 years and 20.1 years in females, respectively and age at attainment of peak BMD varied by skeletal sites and sex. The study also found that females achieved peak femoral neck, total hip and lumbar spine BMD earlier than males (all P < 0.001); race and BMI were not associated with the age at attainment of peak BMD (all P > 0.05). These results suggested that improving bone health among individuals before 20 years old may be useful for reducing future risk of osteoporosis and osteoporotic fractures.

Evolutionary Perspectives on the Developing Skeleton and Implications for Lifelong Health

Osteoporosis is a significant cause of morbidity and mortality in contemporary populations. This common disease of aging results from a state of bone fragility that occurs with low bone mass and loss of bone quality. Osteoporosis is thought to have origins in childhood. During growth and development, there are rapid gains in bone dimensions, mass, and strength. Peak bone mass is attained in young adulthood, well after the cessation of linear growth, and is a major determinant of osteoporosis later in life. Here we discuss the evolutionary implications of osteoporosis as a disease with developmental origins that is shaped by the interaction among genes, behavior, health status, and the environment during the attainment of peak bone mass. Studies of contemporary populations show that growth, body composition, sexual maturation, physical activity, nutritional status, and dietary intake are determinants of childhood bone accretion, and provide context for interpreting bone strength and osteoporosis in skeletal populations. Studies of skeletal populations demonstrate the role of subsistence strategies, social context, and occupation in the development of skeletal strength. Comparisons of contemporary living populations and archeological skeletal populations suggest declines in bone density and strength that have been occurring since the Pleistocene. Aspects of western lifestyles carry implications for optimal peak bone mass attainment and lifelong skeletal health, from increased longevity to circumstances during development such as obesity and sedentism. In light of these considerations, osteoporosis is a disease of contemporary human evolution and evolutionary perspectives provide a key lens for interpreting the changing global patterns of osteoporosis in human health.

Pubertal timing and adult fracture risk in men: A population-based cohort study

BACKGROUND

Puberty is a critical period for bone mass accrual, and late puberty in boys is associated with reduced bone mass in adult men. The role of variations in pubertal timing within the normal range for adult fracture risk in men is, however, unknown. We, therefore, assessed the association between age at peak height velocity (PHV), an objective measure of pubertal timing, and fracture risk in adult men.

METHODS AND FINDINGS

In the BMI Epidemiology Study Gothenburg, 31,971 Swedish men born between January 1, 1945, and December 31, 1961, with detailed growth data (height and weight) available from centrally archived school healthcare records and the conscription register were followed until December 31, 2016. Age at PHV was calculated according to a modified infancy-childhood-puberty model, and fracture information was retrieved from the Swedish National Patient Register. The mean ± SD age at PHV was 14.1 ± 1.1 years. In total, 5,872 men (18.4%) sustained at least 1 fracture after 20 years of age and 5,731 men (17.9%) sustained a non-vertebral fracture after 20 years of age during a mean ± SD follow-up of 37.3 ± 11.7 years. Cox proportional hazards models adjusted for birth year and country of origin revealed that age at PHV was associated with the risk of any fracture and non-vertebral fracture. Participants with age at PHV in the highest tertile (after 14.5 years of age) were at greater risk of any fracture (hazard ratio [HR] 1.15, 95% confidence interval [CI] 1.08-1.22, P < 0.001) and non-vertebral fracture (HR 1.16, 95% CI 1.09-1.24, P < 0.001) compared with those with age at PHV in the lowest tertile (at 13.6 years of age or younger). Additional adjustments for birthweight, childhood BMI, adult educational level, and young adult height did not attenuate the associations between age at PHV and adult fracture risk. Limitations of this study include the inability to adjust for important risk factors for fracture, inadequate power to assess the relation between pubertal timing and specific fracture types, and the limited generalizability to other populations.

CONCLUSIONS

In this study, we observed that late pubertal timing was associated with increased adult fracture risk in men. These findings suggest that information on pubertal timing might aid in the identification of those men at greatest risk of fracture.

Effects of the Timing of Sex-Steroid Exposure in Adolescence on Adult Health Outcomes

CONTEXT

Variation in pubertal timing is associated with a wide range of adult risks and outcomes, but it is unclear whether these associations are causal, and it is largely unknown whether these associations can be modified by treatment.

EVIDENCE ACQUISITION

We conducted PubMed searches to identify Mendelian randomization (MR) studies on the influence of pubertal timing on adult health and studies on sex-steroid treatment of the following conditions associated with reduced reproductive endocrine function in adolescence: constitutional delay, Turner syndrome, and Klinefelter syndrome.

EVIDENCE SYNTHESIS

Results of MR studies suggest that earlier pubertal timing increases body mass index; increases risk for breast, ovarian, endometrial, and prostate cancers; elevates fasting glucose levels and blood pressure; impairs lung capacity and increases risk for asthma; leads to earlier sexual intercourse and first birth; decreases time spent in education; and increases depressive symptoms in adolescence. Later pubertal timing appears to lower bone mineral density (BMD). Although studies of constitutional delay have not shown that sex-steroid treatment alters adult height or BMD, studies of girls with Turner syndrome and boys with Klinefelter syndrome suggest that earlier initiation of sex-steroid treatment improves physical and neurocognitive outcomes.

CONCLUSIONS

Despite having some limitations, MR studies suggest that pubertal timing causally influences many adult conditions and disease risks. Studies of Turner syndrome and Klinefelter syndrome suggest that earlier sex-steroid exposure may have short- and long-term benefits. The mechanisms underlying these findings and the effects of trends and treatments affecting pubertal timing remain to be determined.

Association Between Age at Puberty and Bone Accrual From 10 to 25 Years of Age

Importance

Bone health in early life is thought to influence the risk of osteoporosis in later life.

Objective

To examine whether puberty timing is associated with bone mineral density accrual up to adulthood.

Design, Setting, and Participants

This cohort study used data from the Avon Longitudinal Study of Parents and Children, a prospective population-based birth cohort initiated in 1991 to 1992 in southwest England. The participants were 6389 healthy British people who underwent regular follow-up, including up to 6 repeated bone density scans from ages 10 to 25 years. Data analysis was performed from June 2018 to June 2019.

Exposures

Age at puberty from estimated age at peak height velocity (years).

Main Outcomes and Measures

Gains per year in whole-body bone mineral density (grams per square centimeter), assessed by dual-energy x-ray absorptiometry at ages 10, 12, 14, 16, 18, and 25 years and modeled using linear splines.

Results

A total of 6389 participants (3196 [50.0%] female) were included. The mean (SD) age at peak height velocity was 13.5 (0.9) years for male participants and 11.6 (0.8) years for female participants. Male participants gained bone mineral density at faster rates than did female participants, with the greatest gains in both male participants (0.139 g/cm2/y; 95% CI, 0.127-0.151 g/cm2/y) and female participants (0.106 g/cm2/y; 95% CI, 0.098-0.114 g/cm2/y) observed between the year before and 2 years after peak height velocity. When aligned by chronological age, per 1-year older age at puberty was associated with faster subsequent gains in bone mineral density; the magnitudes of faster gains were greatest between ages 14 and 16 years in both male participants (0.013 g/cm2/y; 95% CI, 0.011-0.015 g/cm2/y) and female participants (0.014 g/cm2/y; 95% CI, 0.014-0.015 g/cm2/y), were greater in male participants (0.011 g/cm2/y; 95% CI, 0.010-0.013 g/cm2/y) than in female participants (0.003 g/cm2/y; 95% CI, 0.003-0.004 g/cm2/y) between ages 16 and 18 years, and were least in both male participants (0.002 g/cm2/y; 95% CI, 0.001-0.003 g/cm2/y) and female participants (0.000 g/cm2/y; 95% CI, -0.001 to 0.000 g/cm2/y) between ages 18 and 25 years. Despite faster gains, older age at puberty was associated with persistently lower bone mineral density, changing from 0.050 g/cm2 (95% CI, -0.056 to -0.045 g/cm2) lower at age 14 years to 0.047 g/cm2 (95% CI, -0.051 to -0.043 g/cm2) lower at age 25 years in male participants and from 0.044 g/cm2 (95% CI, -0.046 to -0.041 g/cm2) to 0.034 g/cm2 (95% CI, -0.036 to -0.032 g/cm2) lower at the same ages in female participants.

Conclusions and Relevance

People with older pubertal age should be advised on how to maximize bone mineral density and minimize its decrease in later life to help prevent fracture and osteoporosis.

Endocrine parameters in association with bone mineral accrual in young female vocational ballet dancers

Less is known on bone mass gains in dancers involved in vocational dance training. The present study found that, as young vocational dancers progress on their professional training, their bone health remains consistently lower compared to non-exercising controls. Endocrine mechanisms do not seem to explain these findings.

PURPOSE

Little is known on bone mass development in dancers involved in vocational training. The aim of the present study was to model bone mineral content (BMC) accruals and to determine whether circulating levels of oestrogens, growth hormone (GH), and insulin-like growth factor I (IGF-1) explain differences in bone mass gains between vocational dance students and matched controls.

METHODS

The total of 67 vocational female dancers (VFDs) and 68 aged-matched controls (12.1 ± 1.9 years and 12.7 ± 2.0 years at baseline, respectively) were followed for two consecutive years (34 VFD and 31 controls remained in the study for the full duration). BMC was evaluated annually at impact [femoral neck (FN); lumbar spine (LS)] and non-impact sites (forearm) using DXA. Anthropometry, age at menarche (questionnaire), and hormone serum concentrations (immunoradiometric assays) were also assessed for the same period.

RESULTS

VFD demonstrated consistently reduced body weight (p < 0.001) and BMC at all three anatomical sites (p < 0.001) compared to controls throughout the study period. Menarche, body weight, GH, and IGF-1 were significantly associated with bone mass changes over time (p < 0.05) but did not explain group differences in BMC gains at impact sites (p > 0.05). However, body weight did explain the differences between groups in terms of BMC gains at the forearm (non-impact site).

CONCLUSION

Two consecutive years of vocational dance training revealed that young female dancers demonstrate consistently lower bone mass compared to controls at both impact and non-impact sites. The studied endocrine parameters do not seem to explain group differences in terms of bone mass gains at impact sites.

Genetically Determined Later Puberty Impacts Lowered Bone Mineral Density in Childhood and Adulthood

Later puberty associates with lower areal bone mineral density (aBMD), and both are risk factors for osteoporosis. However, the association between puberty timing-associated genetic variants and aBMD during development, and the causal relationship between puberty timing and aBMD, remain uncharacterized. We constructed sex-specific polygenic risk scores (GRS) consisting of 333 genetic variants associated with later puberty in European-descent children in the Bone Mineral Density in Childhood Study (BMDCS), consisting of a longitudinal cohort with up to seven assessments (n = 933) and a cross-sectional cohort (n = 486). These GRS were tested for associations with age- and sex-specific aBMD Z-scores at the lumbar spine (LS), femoral neck (FN), total hip, and distal radius, accounting for clinical covariates using sex-stratified linear mixed models. The causal relationship between puberty timing and aBMD was tested in the BMDCS and in publicly available adult data (GEFOS consortium) using two-sample Mendelian randomization (MR). The puberty-delaying GRS was associated with later puberty and lower LS-aBMD in the BMDCS in both sexes (combined beta ± SE = -0.078 ± 0.024; p = 0.0010). In the MR framework, the puberty-delaying genetic instrument also supported a causal association with lower LS-aBMD and FN-aBMD in adults of both sexes. Our results suggest that pubertal timing is causal for diminished aBMD in a skeletal site- and sex-specific manner that tracks throughout life, potentially impacting later risk for osteoporosis, which should be tested in future studies. © 2017 American Society for Bone and Mineral Research.

Modelling height in adolescence: a comparison of methods for estimating the age at peak height velocity

BACKGROUND

Controlling for maturational status and timing is crucial in lifecourse epidemiology. One popular non-invasive measure of maturity is the age at peak height velocity (PHV). There are several ways to estimate age at PHV, but it is unclear which of these to use in practice.

AIM

To find the optimal approach for estimating age at PHV.

SUBJECTS AND METHODS

Methods included the Preece & Baines non-linear growth model, multi-level models with fractional polynomials, SuperImposition by Translation And Rotation (SITAR) and functional data analysis. These were compared through a simulation study and using data from a large cohort of adolescent boys from the Christ's Hospital School.

RESULTS

The SITAR model gave close to unbiased estimates of age at PHV, but convergence issues arose when measurement error was large. Preece & Baines achieved close to unbiased estimates, but shares similarity with the data generation model for our simulation study and was also computationally inefficient, taking 24 hours to fit the data from Christ's Hospital School. Functional data analysis consistently converged, but had higher mean bias than SITAR. Almost all methods demonstrated strong correlations (r > 0.9) between true and estimated age at PHV.

CONCLUSIONS

Both SITAR or the PBGM are useful models for adolescent growth and provide unbiased estimates of age at peak height velocity. Care should be taken as substantial bias and variance can occur with large measurement error.

Endocrine Treatment of Gender-Dysphoric/Gender-Incongruent Persons: An Endocrine Society Clinical Practice Guideline

OBJECTIVE

To update the "Endocrine Treatment of Transsexual Persons: An Endocrine Society Clinical Practice Guideline," published by the Endocrine Society in 2009.

PARTICIPANTS

The participants include an Endocrine Society-appointed task force of nine experts, a methodologist, and a medical writer.

EVIDENCE

This evidence-based guideline was developed using the Grading of Recommendations, Assessment, Development, and Evaluation approach to describe the strength of recommendations and the quality of evidence. The task force commissioned two systematic reviews and used the best available evidence from other published systematic reviews and individual studies.

CONSENSUS PROCESS

Group meetings, conference calls, and e-mail communications enabled consensus. Endocrine Society committees, members and cosponsoring organizations reviewed and commented on preliminary drafts of the guidelines.

CONCLUSION

Gender affirmation is multidisciplinary treatment in which endocrinologists play an important role. Gender-dysphoric/gender-incongruent persons seek and/or are referred to endocrinologists to develop the physical characteristics of the affirmed gender. They require a safe and effective hormone regimen that will (1) suppress endogenous sex hormone secretion determined by the person's genetic/gonadal sex and (2) maintain sex hormone levels within the normal range for the person's affirmed gender. Hormone treatment is not recommended for prepubertal gender-dysphoric/gender-incongruent persons. Those clinicians who recommend gender-affirming endocrine treatments-appropriately trained diagnosing clinicians (required), a mental health provider for adolescents (required) and mental health professional for adults (recommended)-should be knowledgeable about the diagnostic criteria and criteria for gender-affirming treatment, have sufficient training and experience in assessing psychopathology, and be willing to participate in the ongoing care throughout the endocrine transition. We recommend treating gender-dysphoric/gender-incongruent adolescents who have entered puberty at Tanner Stage G2/B2 by suppression with gonadotropin-releasing hormone agonists. Clinicians may add gender-affirming hormones after a multidisciplinary team has confirmed the persistence of gender dysphoria/gender incongruence and sufficient mental capacity to give informed consent to this partially irreversible treatment. Most adolescents have this capacity by age 16 years old. We recognize that there may be compelling reasons to initiate sex hormone treatment prior to age 16 years, although there is minimal published experience treating prior to 13.5 to 14 years of age. For the care of peripubertal youths and older adolescents, we recommend that an expert multidisciplinary team comprised of medical professionals and mental health professionals manage this treatment. The treating physician must confirm the criteria for treatment used by the referring mental health practitioner and collaborate with them in decisions about gender-affirming surgery in older adolescents. For adult gender-dysphoric/gender-incongruent persons, the treating clinicians (collectively) should have expertise in transgender-specific diagnostic criteria, mental health, primary care, hormone treatment, and surgery, as needed by the patient. We suggest maintaining physiologic levels of gender-appropriate hormones and monitoring for known risks and complications. When high doses of sex steroids are required to suppress endogenous sex steroids and/or in advanced age, clinicians may consider surgically removing natal gonads along with reducing sex steroid treatment. Clinicians should monitor both transgender males (female to male) and transgender females (male to female) for reproductive organ cancer risk when surgical removal is incomplete. Additionally, clinicians should persistently monitor adverse effects of sex steroids. For gender-affirming surgeries in adults, the treating physician must collaborate with and confirm the criteria for treatment used by the referring physician. Clinicians should avoid harming individuals (via hormone treatment) who have conditions other than gender dysphoria/gender incongruence and who may not benefit from the physical changes associated with this treatment.

Bone mass of female dance students prior to professional dance training: A cross-sectional study

Background

Professional dancers are at risk of developing low bone mineral density (BMD). However, whether low BMD phenotypes already exist in pre-vocational dance students is relatively unknown.

Aim

To cross-sectionally assess bone mass parameters in female dance students selected for professional dance training (first year vocational dance students) in relation to aged- and sex-matched controls.

Methods

34 female selected for professional dance training (10.9yrs ±0.7) and 30 controls (11.1yrs ±0.5) were examined. Anthropometry, pubertal development (Tanner) and dietary data (3-day food diary) were recorded. BMD and bone mineral content (BMC) at forearm, femur neck (FN) and lumbar spine (LS) were assessed using Dual-Energy X-Ray Absorptiometry. Volumetric densities were estimated by calculating bone mineral apparent density (BMAD).

Results

Dancers were mainly at Tanner pubertal stage I (vs. stage IV in controls, p<0.001), and demonstrated significantly lower body weight (p<0.001) and height (p<0.01) than controls. Calorie intake was not different between groups, but calcium intake was significantly greater in dancers (p<0.05). Dancers revealed a significantly lower BMC and BMD values at all anatomical sites (p<0.001), and significantly lower BMAD values at the LS and FN (p<0.001). When adjusted for covariates (body weight, height, pubertal development and calcium intake), dance students continued to display a significantly lower BMD and BMAD at the FN (p<0.05; p<0.001) at the forearm (p<0.01).

Conclusion

Before undergoing professional dance training, first year vocational dance students demonstrated inferior bone mass compared to controls. Longitudinal models are required to assess how bone health-status changes with time throughout professional training.

Estrogens and Androgens in Skeletal Physiology and Pathophysiology

Estrogens and androgens influence the growth and maintenance of the mammalian skeleton and are responsible for its sexual dimorphism. Estrogen deficiency at menopause or loss of both estrogens and androgens in elderly men contribute to the development of osteoporosis, one of the most common and impactful metabolic diseases of old age. In the last 20 years, basic and clinical research advances, genetic insights from humans and rodents, and newer imaging technologies have changed considerably the landscape of our understanding of bone biology as well as the relationship between sex steroids and the physiology and pathophysiology of bone metabolism. Together with the appreciation of the side effects of estrogen-related therapies on breast cancer and cardiovascular diseases, these advances have also drastically altered the treatment of osteoporosis. In this article, we provide a comprehensive review of the molecular and cellular mechanisms of action of estrogens and androgens on bone, their influences on skeletal homeostasis during growth and adulthood, the pathogenetic mechanisms of the adverse effects of their deficiency on the female and male skeleton, as well as the role of natural and synthetic estrogenic or androgenic compounds in the pharmacotherapy of osteoporosis. We highlight latest advances on the crosstalk between hormonal and mechanical signals, the relevance of the antioxidant properties of estrogens and androgens, the difference of their cellular targets in different bone envelopes, the role of estrogen deficiency in male osteoporosis, and the contribution of estrogen or androgen deficiency to the monomorphic effects of aging on skeletal involution.

Pubertal timing and bone phenotype in early old age: findings from a British birth cohort study

Objectives: To investigate the effect of pubertal timing, assessed in adolescence, on bone size, strength and density in men and women in early old age.

Design: A British birth cohort study with prospective indicators of pubertal timing based on age at menarche, clinical assessment of pubertal stage, and growth tempo from serial height measures, and bone measures derived from peripheral quantitative computed tomography (pQCT) and dual-energy X-ray absorptiometry (DXA) at 60-64 years of age among 866 women and 792 men.

Methods: A first set of regression models investigated the relationships between pubertal timing and bone size, strength and density, adjusting for current height and weight, smoking and adult socioeconomic position. To make an equivalent comparison between men and women, the percentage difference in bone outcomes was calculated for a 5-year difference in age at menarche, and in men a comparison between those who were fully mature or pre-adolescent at 14.5 years. A second set of models investigated the percentage difference in bone outcomes for a 5-year difference in timing of peak height velocity (height tempo) derived from longitudinal growth modelling (Superimposition by Translation and Rotation model; SITAR).

Results: After adjustment for current height and weight, a 5-year increase in age at menarche was associated with an 8% [95% confidence interval (CI) -17%, 0.5%, P = 0.07) lower trabecular volumetric bone mineral density (vBMD); men who were pre-adolescent at 14.5 years had a 9%, (95% CI -14%, -4%; P = 0.001) lower trabecular vBMD compared with those who had been fully mature. Other confounders did not attenuate these estimates further. Patterns of association were similar but somewhat weaker for lumbar spine and total hip areal BMD. Age at peak height velocity was associated with even larger differences in BMD in men and women, and was negatively associated with bone size and strength.

Conclusions: The association between later puberty and lower BMD persists into early old age. The 9-10% lower trabecular vBMD in later compared with earlier maturers could be clinically important given a rate of bone loss from midlife of 1-2% a year and the negative association between BMD and fracture.

The National Osteoporosis Foundation's position statement on peak bone mass development and lifestyle factors: a systematic review and implementation recommendations

Lifestyle choices influence 20-40 % of adult peak bone mass. Therefore, optimization of lifestyle factors known to influence peak bone mass and strength is an important strategy aimed at reducing risk of osteoporosis or low bone mass later in life. The National Osteoporosis Foundation has issued this scientific statement to provide evidence-based guidance and a national implementation strategy for the purpose of helping individuals achieve maximal peak bone mass early in life. In this scientific statement, we (1) report the results of an evidence-based review of the literature since 2000 on factors that influence achieving the full genetic potential for skeletal mass; (2) recommend lifestyle choices that promote maximal bone health throughout the lifespan; (3) outline a research agenda to address current gaps; and (4) identify implementation strategies. We conducted a systematic review of the role of individual nutrients, food patterns, special issues, contraceptives, and physical activity on bone mass and strength development in youth. An evidence grading system was applied to describe the strength of available evidence on these individual modifiable lifestyle factors that may (or may not) influence the development of peak bone mass (Table 1). A summary of the grades for each of these factors is given below. We describe the underpinning biology of these relationships as well as other factors for which a systematic review approach was not possible. Articles published since 2000, all of which followed the report by Heaney et al. [1] published in that year, were considered for this scientific statement. This current review is a systematic update of the previous review conducted by the National Osteoporosis Foundation [1]. [Table: see text] Considering the evidence-based literature review, we recommend lifestyle choices that promote maximal bone health from childhood through young to late adolescence and outline a research agenda to address current gaps in knowledge. The best evidence (grade A) is available for positive effects of calcium intake and physical activity, especially during the late childhood and peripubertal years-a critical period for bone accretion. Good evidence is also available for a role of vitamin D and dairy consumption and a detriment of DMPA injections. However, more rigorous trial data on many other lifestyle choices are needed and this need is outlined in our research agenda. Implementation strategies for lifestyle modifications to promote development of peak bone mass and strength within one's genetic potential require a multisectored (i.e., family, schools, healthcare systems) approach.

The endocrine role of estrogens on human male skeleton

Before the characterization of human and animal models of estrogen deficiency, estrogen action was confined in the context of the female bone. These interesting models uncovered a wide spectrum of unexpected estrogen actions on bone in males, allowing the formulation of an estrogen-centric theory useful to explain how sex steroids act on bone in men. Most of the principal physiological events that take place in the developing and mature male bone are now considered to be under the control of estrogen. Estrogen determines the acceleration of bone elongation at puberty, epiphyseal closure, harmonic skeletal proportions, the achievement of peak bone mass, and the maintenance of bone mass. Furthermore, it seems to crosstalk with androgen even in the determination of bone size, a more androgen-dependent phenomenon. At puberty, epiphyseal closure and growth arrest occur when a critical number of estrogens is reached. The same mechanism based on a critical threshold of serum estradiol seems to operate in men during adulthood for bone mass maintenance via the modulation of bone formation and resorption in men. This threshold should be better identified in-between the ranges of 15 and 25 pg/mL. Future basic and clinical research will optimize strategies for the management of bone diseases related to estrogen deficiency in men.

Androgens and estrogens in skeletal sexual dimorphism

Bone is an endocrine tissue expressing androgen and estrogen receptors as well as steroid metabolizing enzymes. The bioactivity of circulating sex steroids is modulated by sex hormone-binding globulin and local conversion in bone tissue, for example, from testosterone (T) to estradiol (E2) by aromatase, or to dihydrotestosterone by 5α-reductase enzymes. Our understanding of the structural basis for gender differences in bone strength has advanced considerably over recent years due to increasing use of (high resolution) peripheral computed tomography. These microarchitectural insights form the basis to understand sex steroid influences on male peak bone mass and turnover in cortical vs trabecular bone. Recent studies using Cre/LoxP technology have further refined our mechanistic insights from global knockout mice into the direct contributions of sex steroids and their respective nuclear receptors in osteoblasts, osteoclasts, osteocytes, and other cells to male osteoporosis. At the same time, these studies have reinforced the notion that androgen and estrogen deficiency have both direct and pleiotropic effects via interaction with, for example, insulin-like growth factor 1, inflammation, oxidative stress, central nervous system control of bone metabolism, adaptation to mechanical loading, etc., This review will summarize recent advances on these issues in the field of sex steroid actions in male bone homeostasis.

Assessing bone health in children and adolescents

During normal childhood and adolescence, the skeleton undergoes tremendous change. Utilizing the processes of modeling and remodeling, the skeleton acquires its adult configuration and ultimately achieves peak bone mass. Optimization of peak bone mass requires the proper interaction of environmental, dietary, hormonal, and genetic influences. A variety of acute and chronic conditions, as well as genetic polymorphisms, are associated with reduced bone density, which can lead to an increased risk of fracture both in childhood and later during adulthood. Bone densitometry has an established role in the evaluation of adults with bone disorders, and the development of suitable reference ranges for children now permits the application of this technology to younger individuals. We present a brief overview of the factors that determine bone density and the emerging role of bone densitometry in the assessment of bone mass in growing children and adolescents.