Bone mineral density and hormone levels in menopausal Australian women

Independent Skeletal Actions of Pituitary Hormones

Over the past years, pituitary hormones and their receptors have been shown to have non-traditional actions that allow them to bypass the hypothalamus-pituitary-effector glands axis. Bone cells-osteoblasts and osteoclasts-express receptors for growth hormone, follicle stimulating hormone (FSH), thyroid stimulating hormone (TSH), adrenocorticotrophic hormone (ACTH), prolactin, oxytocin, and vasopressin. Independent skeletal actions of pituitary hormones on bone have been studied using genetically modified mice with haploinsufficiency and by activating or inactivating the receptors pharmacologically, without altering systemic effector hormone levels. On another front, the discovery of a TSH variant (TSH-βv) in immune cells in the bone marrow and skeletal action of FSHβ through tumor necrosis factor α provides new insights underscoring the integrated physiology of bone-immune-endocrine axis. Here we discuss the interaction of each pituitary hormone with bone and the potential it holds in understanding bone physiology and as a therapeutic target.

Cohort profile: Women's Healthy Ageing Project (WHAP) - a longitudinal prospective study of Australian women since 1990

Background

The cohort was commenced to examine women’s health from midlife (45–55 years) before the menopausal transition and into ageing.

Methods

Randomised selection and assessment of 2,001 women living in the Melbourne metropolitan area was conducted by the Roy Morgan Centre in 1990/91. Of the 779 women who met the entry criteria for the longitudinal follow-up (aged 45–55 years, menstruating, having a uterus and at least one ovary and not taking hormone therapy) 438 agreed to be seen annually across the menopausal transition from 1992 to 1999. Longitudinal prospective follow-up since 2000 has continued intermittently (2002/03, 2004/05, 2012/13, 2014/15). Data collection has included fasting biomarkers in each year since 1992, clinical assessment, lifestyle and quality of life data, physical measures and validated questionnaire data. Participants have consented to data linkage and, to date, mammogram and BioGrid data have been accessed. Biobank storage including serum, deoxyribonucleic acid (DNA) storage and PAXgene tubes are maintained.

Discussion

The WHAP has contributed to over 200 published research findings, several books, and book chapters in a variety of areas, including: health and wellbeing; mental and cognitive health; bone health; lifestyle, vascular risk and prevention; women’s health and hormonal transition; and cross-cultural research.

With all participants now aged over 70 years, the cohort is ideally placed to answer key questions of healthy ageing in women. With more than 25 years of longitudinal prospective follow-up this Australian dataset is unique in its duration, breadth and detail of measures including clinical review and specialized disease-specific testing and biomarkers. Ongoing follow-up into older ages for this long-running cohort will enable the association between mid to late-life factors and healthy ageing to be determined. This is particularly valuable for the examination of chronic diseases which have a 20–30 year prodrome and to provide knowledge on multiple morbidities. The dataset has a unique opportunity to improve our understanding of temporal relationships and the interactions between risk factors and comorbidities.

Electronic supplementary material

The online version of this article (doi:10.1186/s40695-016-0018-y) contains supplementary material, which is available to authorized users.

Inhibin A enhances bone formation during distraction osteogenesis

Given the aging population and the increased incidence of fracture in the elderly population, the need exists for agents that can enhance bone healing, particularly in situations of delayed fracture healing and/or non-union. Our previous studies demonstrated that overexpression of the gonadal peptide, human inhibin A (hInhA), in transgenic mice enhances bone formation and strength via increased osteoblast activity. We tested the hypothesis that hInhA can also exert anabolic effects in a murine model of distraction osteogenesis (DO), using both transgenic hInhA overexpression and administration of normal physiological levels of hInhA in adult male Swiss-Webster mice. Tibial osteotomies and external ring fixation were performed, followed by a 3-day latency period, 14-day distraction, and sacrifice on day 18. Supraphysiological levels of hInhA in transgenic mice, but not normal physiological levels of hInhA, significantly increased endosteal bone formation and mineralized bone area in the distraction gap, as determined by radiographic and µCT analysis. Significantly, increased PCNA and osteocalcin expression in the primary matrix front suggested that hInhA increased osteoblast proliferation. This mechanism is consistent with the effects of other agents and pathologies that modulate bone formation during DO, and demonstrates the potential of hInhA to enhance bone repair and regeneration.

The menopausal transition: a 9-year prospective population-based study. The Melbourne Women's Midlife Health Project

OBJECTIVES

To describe the natural history of the menopause in Australian-born women. To determine the hormonal changes relating to the menopausal transition (MT) and how these affect quality of life, bone mineral density, body composition, cardiovascular disease (CVD) risk and memory.

DESIGN

A 9-year prospective, observational study of a population-based sample of 438 Australian-born women aged 45-55 years at baseline. By the 9th year, the retention rate was 88%. Interviews, blood sampling, menstrual calendars, quality of life and physical measures were taken annually, and bone mineral density was measured bi-annually.

RESULTS

The late MT coincides with changes in estradiol, follicle stimulating hormone, and free testosterone index, decreases in bone density and mastalgia, and increases in central adiposity, vasomotor symptoms, insomnia and vaginal dryness. Levels of total testosterone and dehydroepiandrosterone sulfate are unchanged by the MT. An increase in CVD risk was associated with increases in weight and free testosterone index and a decrease in estradiol. Depressed mood is increased by symptoms and by stressors occurring in the MT. Sexual functioning significantly deteriorates with the MT and aging, but relational factors have major effects. Menstrual cycles became more variable and longer closer to the final menstrual period.

CONCLUSIONS

As hormonal changes during the MT directly or indirectly adversely affect quality of life, body composition and CVD risk, maintenance of health parameters in the premenopausal years is crucial for a healthy postmenopause.

Inhibin A is an endocrine stimulator of bone mass and strength

Gonadal function plays a major role in bone homeostasis. It is widely held that the skeletal consequences of hypogonadism are solely due to a loss of sex steroids; however, increases in bone turnover begin during perimenopause before decreases in serum estradiol levels. These data and our demonstration that inhibins acutely regulate bone cell differentiation in vitro led us to test whether inhibin A (InhA) regulates bone mass in vivo. Using a transgenic model of inducible human InhA expression, InhA increased total body bone mineral density, increased bone volume, and improved biomechanical properties at the proximal tibia in intact mice and also prevented the loss of BMD and bone volume and strength associated with gonadectomy at both the spine and proximal tibia. In addition, InhA increased mineral apposition rate, double-labeled surface, and serum osteocalcin levels in vivo and osteoblastogenesis ex vivo without affecting osteoclast number or activity. Together these results demonstrate novel stimulatory effects of InhA on the skeleton in vivo. These studies provide in vivo evidence demonstrating that gonadal factors other than sex steroids play an important role in regulating bone mass and strength and, combined with our previous clinical data, suggest that gonadal InhA may be a component of the normal endocrine repertoire that regulates bone quality in both the axial and appendicular skeleton.

Physical activity: measurement in mid-life women

OBJECTIVES

To review methods of assessing physical activity, and to compare two different questionnaires that were administered in the Melbourne Women's Midlife Health Project (MWMHP).

METHODS

Cross-sectional and subsequent longitudinal population-based study of Australian-born women who were aged 45-55 at baseline. Self-administered modified form of the Minnesota Leisure-Time Physical Activity questionnaire and interviewer-administered short physical activity question.

RESULTS

Two hundred and ninety-two women completed the Minnesota Leisure-Time Physical Activity questionnaire at both cross-sectional and 3rd year of follow-up (L3) and there was no difference in the total mean time spent exercising at both phases [5.9 (SD, 5.7) and 5.8 (SD, 5.0) hours per week, respectively]. The responses to the two questionnaires were significantly associated (beta = -0.89, SE 0.17, p < 0.0005). Using the Minnesota Leisure-Time Physical Activity questionnaire between the cross-sectional and L3 phases, 10% of the women increased the time they spent exercising by 5 h per week and 10% decreased it by the same amount. Using the short exercise question, 12% of women decreased their participation by two or more sessions per week and 14% increased their participation by this amount between the cross-sectional and L3 phases.

CONCLUSION

In this cohort of mid-life women the short exercise question was comparable in terms of measuring participation and change in physical activity with the more complex Minnesota Leisure-Time Physical Activity questionnaire.

A meta-analysis of the effects of cigarette smoking on bone mineral density

To determine the magnitude and mediators of the association between cigarette smoking and bone mass in the epidemiologic literature we reviewed articles, published abstracts, and conference proceedings, identified through MEDLINE, psychological abstracts, conference proceedings, and article bibliographies. We studied cross-sectional and prospective human studies that provided a quantitative measure of bone mass (X-ray, absorptiometry, or computed tomography) as a function of cigarette smoking exposure. Effects were expressed as pooled standardized mean differences for categorical comparisons (e.g., bone mass in current versus nonsmokers), and as pooled correlation coefficients for continuous comparisons (e.g., correlation of bone mass and pack-years of smoking). Effects were derived for combined bone sites (all bone sites pooled within each study) and four specific sites (hip, lumbar spine, forearm, and os calcis), and were examined overall and as a function of subject and methodologic characteristics (gender, age, body weight, menopausal status, health status). Data were pooled across 86 studies, enrolling 40,753 subjects. Smokers had significantly reduced bone mass compared with nonsmokers (never and former smokers) at all bone sites, averaging a one-tenth standard deviation (SD) deficit for combined sites. Deficits were especially pronounced at the hip, where the bone mass of current smokers was one-third of a SD less than that of never smokers. Overall, effects were greatest in men and in the elderly, and were dose-dependent. In prospective studies, smokers had greater rates of bone loss over time compared with nonsmokers. Bone mass differences remained significant after controlling for age and body weight differences between the two groups. Absolute effect sizes at most bone sites were greatest for current smokers compared with never smokers, intermediate for current smokers compared with former smokers, and lowest for former smokers compared with never smokers, suggesting that smoking cessation may have a positive influence on bone mass. Based on these data, it is estimated that smoking increases the lifetime risk of developing a vertebral fracture by 13% in women and 32% in men. At the hip, smoking is estimated to increase lifetime fracture risk by 31% in women and 40% in men. It appears that smoking has an independent, dose-dependent effect on bone loss, which increases fracture risk, and may be partially reversed by smoking cessation. Given the public health implications of smoking on bone health, it is important that this information be incorporated into smoking prevention and cessation efforts.