Risk factors for low bone mineral density among females: the effect of lean body mass

Response of parathyroid hormone to exercise and bone mineral density in adolescent female athletes

BACKGROUND

This study investigates 1) the effects of amount of exercise on levels of serum parathyroid hormone (PTH) and calcium, and 2) the relationship between PTH response and bone mineral density in adolescent female athletes.

SUBJECTS

Twenty-one female athletes on a top-ranked high school basketball team in Japan participated in a one-month intensive basketball program. Subjects were divided into moderate-exercise and strenuous-exercise groups.

METHODS

The amount of exercise was quantified using estimated metabolic equivalent (METs) and exercise hours. Levels of serum intact-PTH and calcium were examined five times: twice before training to establish a baseline (T(-1) and T(0)), once 3rd week of the training period (T(1), once immediately at the end of the program (T(2)), and again one week later(3)). Bone mineral density of forearm (distal-BMD) was measured one week after the end of the program. PTH levels at T(1), T(2) and(3) were regressed on PTH at baseline (T(0)) for both groups and examined for statistical significance. Multiple regression analyses of the changes of PTH and distal-BMD were conducted.

RESULTS

1) Strenuous-exercise subjects showed both increased and decreased PTH levels, while moderate-exercise subjects showed a uniform decrease in PTH throughout the exercise period. 2) Increased PTH was an independent negative predictor of distal-BMD, while high lean body mass, increased serum Ca, and exercise volume were positive predictors.

CONCLUSION

The amount of exercise affects PTH response: moderate exercise suppresses PTH secretion, while strenuous exercise is apt to induce continuous secretion, which has a negative effect on BMD.

Risk factors for low bone mass in healthy 40-60 year old women: a systematic review of the literature

Based on a systematic review of the literature, only low body weight and menopausal status can be considered with confidence, as important risk factors for low BMD in healthy 40-60 year old women. The use of body weight to identify high risk women may reduce unnecessary BMD testing in this age group.

INTRODUCTION

BMD testing of perimenopausal women is increasing but may be unnecessary as fracture risk is low. Appropriate assessment among younger women requires identification of risk factors for low BMD specific to this population.

METHODS

We conducted a systematic literature review of risk factors for low BMD in healthy women aged 40-60 years. Articles were retrieved from six databases and reviewed for eligibility and methodological quality. A grade for overall strength of evidence for each risk factor was assigned.

RESULTS

There was good evidence that low body weight and post-menopausal status are risk factors for low BMD. There was good or fair evidence that alcohol and caffeine intake, and reproductive history are not risk factors. There was inconsistent or insufficient evidence for the effect of calcium intake, physical activity, smoking, age at menarche, history of amenorrhea, family history of OP, race and current age on BMD.

CONCLUSIONS

Based on current evidence in Caucasians, we suggest that, in healthy women aged 40-60 years, only those with a low body weight (< 70 kg) be selected for BMD testing. Further research is necessary to determine optimal race-specific discriminatory weight cut-offs and to evaluate the risk factors for which there was inconclusive evidence.

Correlation between bone mineral density and body composition in Japanese females aged 18-40 years with low forearm bone mineral density

OBJECTIVES

To clarify the relationship between bone mineral density (BMD) and body composition in Japanese women aged 18-40 years with low forearm BMD.

METHODS

The subjects were Japanese 199 women who had been selected for inclusion in the study based on a low forearm BMD determined at the Annual Women's Health Examination. The subjects' mean (+/- standard deviation) age, body height, body weight, and body mass index (BMI) were 33.5 (+/-4.3) years, 158.1 (+/-5.1) cm, 49.6 (+/-5.7) kg, and 19.8 (+/-2.1), respectively. The BMD of the lumbar spine, total body, and left arm were measured using dual-energy X-ray absorptiometry (DXA). Fat mass (FM), bone-free lean tissue mass (LTM), and body fat percentage (BF%) were measured simultaneously with DXA.

RESULTS

In the structural equation model, the standardized regression weights for the path from BMI to BMD of all sites were 0.273-0.434. Conversely, the BF% to BMD of the total body and left arm were -0.192 and -0.296, respectively. In multiple regression analysis, the FM index (FMI) was significantly associated with the BMD of the lumbar spine as a weight-bearing site. The LTM index (LTMI) was significantly associated with the BMD of the total body and left arm as a non-weight-bearing site.

CONCLUSIONS

Young females with low forearm BMD had low body weight and BMI. Thinness was shown to be a risk factor for low BMD, in accordance with results reported elsewhere. A gain in body weight may have the effect of increasing BMD, but our results suggest that to increase BMD, the gain in body weight must include increases in LTM, and not FM alone.

Bone mineral density among female sports participants

Training for and participation in impact-loading sports are associated with alterations in bone strength which are specific to anatomical site and type of strain. The effect of exercise on bone mineral density (BMD) depends on the type of activity engaged in. Sports with high impact loading seem to have a positive effect in promoting bone mineralisation, whereas those with low impacts may have negative or no effects. The aims of the present study were to compare BMD and body composition measures among female participants in three distinctly different sports and investigate differences from sedentary control subjects. Participants were club and university level Rugby Union football players (n = 30, age: 21.4 +/- 1.9 years, height: 1.67 +/- 0.05 m, mass: 73.3 +/- 10.7 kg), netball players (n = 20, 20.7 +/- 1.3 years, 1.68 +/- 0.07 m, 64.3 +/- 7.2 kg), distance runners (n = 11, 21.5 +/- 2.6 years, 1.68 +/- 0.04 m, 57.1 +/- 6.1 kg), and sedentary controls (n = 25, 21.4 +/- 1.1 years; 1.64 +/- 0.07 m, 56.8 +/- 6.8 kg). With the exception of three distance runners, all participants were eumenorrhoeic. Bone mineral density scans were performed for whole-body, left proximal femur, and lumbar spine (L1-4) using dual-energy X-ray absorptiometry. Fat mass, percent body fat, and fat-free soft tissue mass were assessed from whole-body scans. Regional and segmental analysis was also carried out on whole-body BMD data using standard procedures. The runners had a lower fat mass and percent body fat compared to the other sports participants and the controls. All sports groups had higher BMD values than had the controls. Density of bone in the upper body was most pronounced in the rugby football players and least pronounced in the runners. Positive effects were evident at all sites for the rugby players. There were significant correlations between BMD and fat-free soft tissue mass, BMD and body mass, and BMD and training volume. It is concluded that sports participation has positive effects on BMD. The effects are site-specific and depend on the loading characteristics of the sport.

Determining the prevalence of osteoporosis and related factors using quantitative ultrasound in Vietnamese adult women

In 2003, the authors conducted a population-based, cross-sectional survey to determine the prevalence of osteoporosis and related factors in Vietnamese adult women by using quantitative ultrasound at the heel bone (calcaneus). A total of 2,232 adult women aged > or =20 years, living in Hanoi City, and free of illnesses affecting bone metabolism were randomly selected to participate in the study. Subjects' bone mass was assessed by speed of sound at the calcaneus, referred to as quantitative ultrasound measurement. The T-score threshold, defined as < or =-1.8, was used to identify subjects with osteoporosis. The crude prevalence of osteoporosis in Hanoi City was 15.4%; after adjustment for age, it was 9.0%. Among premenopausal women, the crude prevalence of osteoporosis was higher in the urban areas compared with the rural areas. By contrast, postmenopausal women in the rural areas had a higher prevalence of osteoporosis. Multiple logistic regression analysis revealed that factors associated with low speed of sound were age, menopause, educational level, lifelong occupation, recreational weight-bearing exercise, number of births, and height. Results suggest that osteoporosis is a noteworthy problem in Vietnam, and intervention strategies should be considered to control it, especially in high-risk populations.

Body composition changes with age have gender-specific impacts on bone mineral density

Body weight, smoking, alcohol, physical activity, and diet have been proven to affect bone mineral density (BMD) directly or indirectly. Of these, body weight is perhaps best known to affect BMD. However, there is some debate as to whether lean body mass (LBM) or fat mass (FM), the two components of body weight, most determines BMD. Recently, newer peripheral densitometry devices have been developed, which have the advantages of low cost and portability, and this has made field epidemiologic study of osteoporosis possible. As the number of studies that have focused on the contribution made by body composition to BMD is limited, we investigated the relative contribution of LBM and FM to BMD in healthy Korean subjects. 402 age- and weight-matched subjects over 45 years old were selected from a population-based cohort. The mean ages of men and women were 64.1 +/- 8.7 (mean +/- SD) and 64.2 +/- 12.7 years, and mean weights were 63.0 +/- 8.2 and 63.1 +/- 8.2 kg, respectively. BMD was measured by peripheral dual-energy X-ray absorptiometry (DEXA) and body composition by bioelectrical impedance. Sociodemographic characteristics and physical activities were investigated using a standard questionnaire delivered by face-to-face interview. BMDs were 0.48 +/- 0.01 and 0.37 +/- 0.11 g/cm2 in men and women, respectively. In men, age, weight, body mass index (BMI), LBM, FM, physical activity, smoking, alcohol, and education were significantly correlated with BMD. In women, age, weight, BMI, LBM, FM, education, years since menopause, number of deliveries, and number of children breast-fed were significantly correlated with BMD. By multiple regression, LBM, education, smoking, and alcohol in men, and age, LBM, FM, smoking, and number of delivery in women were independent determinants of BMD. LBM was an important contributor for BMD in men, but both LBM and FM were equally important contributors in female to BMD. This stems from the fact that body composition changes with age differ in men and women. Thus, the augmentation of muscle mass in men and the maintenance of an optimal weight in women act to prevent osteoporosis.

Bone and nutrition in elderly women: protein, energy, and calcium as main determinants of bone mineral density

OBJECTIVE

Nutrition is an important factor in the prevention and treatment of osteoporosis. Our goal was to examine the relationship between various nutrients and bone mass of several skeletal sites in elderly women, taking into account possible confounding variables.

DESIGN/METHODS

A cross-sectional study in 136 healthy Caucasian, postmenopausal women, free of medications known to affect bone was carried out. Bone mineral density (BMD) and body composition (lean and fat tissue) were measured by dual X-ray absorptiometry using specialized software for different skeletal sites. Parathyroid hormone (PTH) and vitamin D, 25(OH)D, as possible confounders, were determined in serum samples. Dietary intake, including all supplements, was assessed by 3-day dietary record and analyzed using Food Processor. Past physical activity and present walking were examined as well and accounted for as potential confounders. Simple and multiple regression models were created to assess the relationships between nutrients and BMD. To examine the co-linear variables and their possible independent association with bone, subgroup analyses were performed.

RESULTS

: Showed independent influence of calcium, energy, and protein, examined separately and in multiple regression models on BMD of several skeletal sites. Magnesium, zinc and vitamin C were significantly related to BMD of several skeletal sites in multiple regression models (controlled for age, fat and lean tissue, physical activity and energy intake), each contributing more than 1% of variance. Serum PTH and 25(OH)D did not show significant association with bone mass.

CONCLUSIONS

Despite the cross-sectional nature of our study we were able to show a significant relationship between BMD and several critical nutrients: energy, protein, calcium, magnesium, zinc and vitamin C. The exact involvement of these nutrients and their clinical significance in bone health need to be further elucidated in humans and conclusions about the effects of a single nutrient on bone mass must be given cautiously, taking into account its interaction and co-linearity with others. Understanding relationships among nutrients, not just limited to calcium and vitamin D, but others that have not been investigated to such extent, is an important step toward identifying preventive measures for bone loss and prevention of osteoporosis.

A nonhuman primate model of age-related bone loss: a longitudinal study in male and premenopausal female rhesus monkeys

Aging is associated with gradual bone loss in men and premenopausal women, with an accelerated rate of loss after menopause in women. Although many studies have investigated bone loss due to surgically induced estrogen depletion, little is known regarding normal age-related changes in bone mass in animal models. We used dual-energy X-ray absorptiometry (DXA) to measure bone mineral density (BMD), bone mineral content (BMC), and projected area (PA) at four skeletal sites over 4 years in 20 premenopausal female (8-23 years) and 29 male (8-27 years) rhesus monkeys (Macaca mulatta). Forearm BMD declined with age in both male and female monkeys. Lean mass was positively associated with BMD at all sites in males and with the distal radius in females. Serum osteocalcin declined and urinary cross-links increased with age in males but not females. Serum 25-hydroxyvitamin D concentrations decreased with age in females, and a similar trend was observed in males. In conclusion, an age-related decline in forearm BMD was observed in male and female rhesus monkeys. Total body BMC declined over time in older females, with a similar trend in males. Changes in markers of bone turnover with age were also observed in male monkeys. The results of this longitudinal study suggest that the rhesus monkey is a potential model for age-related changes in the human skeleton.

Energy restriction does not alter bone mineral metabolism or reproductive cycling and hormones in female rhesus monkeys

Energy restriction (ER) extends the life span and slows aging and age-related diseases in short-lived mammalian species. Although a wide variety of physiological systems have been studied using this paradigm, little is known regarding the effects of ER on skeletal health and reproductive aging. Studies in rhesus monkeys have reported that ER delays sexual and skeletal maturation in young male monkeys and reduces bone mass in adult males. No studies have examined the chronic effects on bone health and reproductive aging in female rhesus monkeys. The present cross-sectional study examined the effects of chronic (6 y) ER on skeletal and reproductive indices in 40 premenopausal and perimenopausal (7-27 y old) female rhesus macaques (Macaca mulatta). Although ER monkeys weighed less and had lower fat mass, ER did not alter bone mineral density, bone mineral content, osteocalcin, 25-hydroxyvitamin D, 1,25-hydroxyvitamin D or parathyroid hormone concentrations, menstrual cycling or reproductive hormone concentrations. Body weight and lean mass were significantly related to bone mineral density and bone mineral content at all skeletal sites (total body, lumbar spine, mid and distal radius; P: < or = 0.04). The number of total menstrual cycles over 2 y, as well as the percentage of normal-length cycles (24-31 d), was lower in older than in younger monkeys (P: < or = 0.05). Older monkeys also had lower estradiol (P: = 0.02) and higher follicle-stimulating hormone (P: = 0.02) concentrations than did younger monkeys. We conclude that ER does not negatively affect these indices of skeletal or reproductive health and does not alter age-associated changes in the same variables.

Association of fractures with caffeine and alcohol in postmenopausal women: the Iowa Women's Health Study

OBJECTIVE

To assess whether alcoholic and caffeinated beverages are associated with risk of fractures in women.

SETTING

Population-based sample surveyed by post.

SUBJECTS

A total of 34 703 postmenopausal Iowan women aged 55-69 years were surveyed.

DESIGN

A cohort of women reported alcoholic and caffeinated beverage intake and were followed for 6.5 years for fracture occurrence. Relative risks (RR) and 95% confidence intervals (CI) were computed using Cox proportional hazards regression. Covariates included age, tobacco use, physical activity, body mass index (BMI), waist to hip ratio (WHR), oestrogen use and calcium intake.

RESULTS

At least one fracture was reported by 4378 women (389 upper arm, 288 forearm, 1128 wrist, 275 hip, 416 vertebral and 2920 other fractures). The adjusted RR for highest versus lowest caffeine intake quintiles was 1.09 (95% CI 0.99-1.21) for combined fracture sites. Wrist fractures were associated positively (RR for extreme quintiles 1.37, 95% CI 1.11-1.69) and upper arm fractures were negatively associated (RR 0.67, 95% CI 0.48-0.94) with caffeine intake. The age-adjusted RR of total fractures for highest versus lowest frequency of beer usage was 1.55 (95% CI 1.25-1.92) and for liquor was 1.25 (95% CI 1.03-1.54). No other association was found between any specific fracture site and alcohol intake.

CONCLUSIONS

We found a modest increase in fracture risk associated with highest caffeine intake, varying by site. Alcohol intake was low, but it also showed a weak positive association with fracture risk.

Response of parathyroid hormone to anaerobic exercise in adolescent female athletes

It has been shown that moderate exercise suppresses parathyroid hormone (PTH) secretion, while strenuous exercise is apt to induce continuous secretion, which has a negative effect on bone mineral densities (BMD). The present study investigated a typical response of PTH to brief exercise. The study group comprised six adolescent female basketball players whose BMD were within normal limits. Maximal anaerobic power by three-step cycling was loaded on each subject. The first blood sample was drawn 30 min prior to testing test, the second was immediately following, the third was 15 min after, and the fourth was 30 min after. The proportional change in plasma volume was -11.5% immediately following (P < 0.05), +2.1% 15 min after, and +5.5% at 30 min after exercise (P < 0.05). The expected value was calculated on the assumption of no effect, except changes in plasma volume, by exercise. The measured values of PTH and calcium (Ca) immediately after exercise were lower than each of the expected values (P < 0.05 for both). At 15 min after, there was no significant difference between expected and measured values of PTH, Ca and magnesium (Mg), respectively. At 30 min after, the measured value of Ca and Mg was higher than each expected value (P < 0.05 for both). It was concluded that PTH secretion is suppressed transiently immediately after maximal anaerobic exercise and is then stimulated during the recovery time in normal BMD subjects.