Physical activity in the prevention and amelioration of osteoporosis in women : interaction of mechanical, hormonal and dietary factors

Osteoporosis is a serious health problem that diminishes quality of life and levies a financial burden on those who fear and experience bone fractures. Physical activity as a way to prevent osteoporosis is based on evidence that it can regulate bone maintenance and stimulate bone formation including the accumulation of mineral, in addition to strengthening muscles, improving balance, and thus reducing the overall risk of falls and fractures. Currently, our understanding of how to use exercise effectively in the prevention of osteoporosis is incomplete. It is uncertain whether exercise will help accumulate more overall peak bone mass during childhood, adolescence and young adulthood. Also, the consistent effectiveness of exercise to increase bone mass, or at least arrest the loss of bone mass after menopause, is also in question. Within this framework, section 1 introduces mechanical characteristics of bones to assist the reader in understanding their responses to physical activity. Section 2 reviews hormonal, nutritional and mechanical factors necessary for the growth of bones in length, width and mineral content that produce peak bone mass in the course of childhood and adolescence using a large sample of healthy Caucasian girls and female adolescents for reference. Effectiveness of exercise is evaluated throughout using absolute changes in bone with the underlying assumption that useful exercise should produce changes that approximate or exceed the absolute magnitude of bone parameters in a healthy reference population. Physical activity increases growth in width and mineral content of bones in girls and adolescent females, particularly when it is initiated before puberty, carried out in volumes and at intensities seen in athletes, and accompanied by adequate caloric and calcium intakes. Similar increases are seen in young women following the termination of statural growth in response to athletic training, but not to more limited levels of physical activity characteristic of longitudinal training studies. After 9-12 months of regular exercise, young adult women often show very small benefits to bone health, possibly because of large subject attrition rates, inadequate exercise intensity, duration or frequency, or because at this stage of life accumulation of bone mass may be at its natural peak. The important influence of hormones as well as dietary and specific nutrient abundance on bone growth and health are emphasised, and premature bone loss associated with dietary restriction and estradiol withdrawal in exercise-induced amenorrhoea is described. In section 3, the same assessment is applied to the effects of physical activity in postmenopausal women. Studies of postmenopausal women are presented from the perspective of limitations of the capacity of the skeleton to adapt to mechanical stress of exercise due to altered hormonal status and inadequate intake of specific nutrients. After menopause, effectiveness of exercise to increase bone mineral depends heavily on adequate availability of dietary calcium. Relatively infrequent evidence that physical activity prevents bone loss or increases bone mineral after menopause may be a consequence of inadequate calcium availability or low intensity of exercise in training studies. Several studies with postmenopausal women show modest increases in bone mineral toward the norm seen in a healthy population in response to high-intensity training. Physical activities continue to stimulate increases in bone diameter throughout the lifespan. These exercise-stimulated increases in bone diameter diminish the risk of fractures by mechanically counteracting the thinning of bones and increases in bone porosity. Seven principles of bone adaptation to mechanical stress are reviewed in section 4 to suggest how exercise by human subjects could be made more effective. They posit that exercise should: (i) be dynamic, not static; (ii) exceed a threshold intensity; (iii) exceed a threshold strain frequency; (iv) be relatively brief but intermittent; (v) impose an unusual loading pattern on the bones; (vi) be supported by unlimited nutrient energy; and (vii) include adequate calcium and cholecalciferol (vitamin D3) availability.     

Effect of exercise on bone: permissive influence of estrogen and calcium

Estrogen deficiency in postmenopausal women is associated with low lumbar bone mineral density and an increased incidence of fractures of the vertebrae and proximal femur. Estrogen deficiency in premenopausal women with secondary amenorrhea related to athletic training or anorexia nervosa is also associated with decreased lumbar bone mineral density. The purpose of this review is to present four concepts related to the adaptations of bone to physical exercise, as a basis to explain the loss of bone mass in women with athletic amenorrhea. These concepts are based on Lanyon's theory of a Minimum Effective Strain-Related Stimulus. The bone remodeling response to estrogen deficiency is an increase in the rate of bone remodeling activity and in the rate of bone resorption relative to formation, resulting in a net loss of bone mass. In the presence of estrogen deficiency, the stimulus of physical activity is thought first to decrease the rate of turnover and secondly to increase bone formation. Endurance exercise training appears to be an insufficient stimulus to accomplish both tasks, which may explain why these athletes often have low lumbar bone mineral density.     

Estrogen and Osteoporosis

In brief: Many aspects of the pathophysiology, prevention, and treatment of osteoporosis are still unclear. However, two facts have emerged over the past ten or so years that now appear incontrovertible: Estrogen deficiency in women results in bone loss, and estrogen treatment in estrogen-deficient women mitigates osteoporosis. This article reviews the use of estrogen in the prevention and treatment of osteoporosis, and only addresses the issue of estrogen deficiency where it is required for clarity.     

Osteoporosis: The state of the art in 1987: A review

Osteoporosis affects approximately 15 to 20 million people in the United States and is the underlying cause of 1.3 million new fractures per year in people over age 45. The more common risk factors recognized in this disorder are older age, female sex, white race, physical inactivity, and early menopause. We now have available equipment which can measure bone density at various sites. These include single- and dual-photon densitometry, and single and dual quantitative computed tomography. These procedures are a quantum improvement over plain x-ray in the assessment of the severity of osteoporosis, but measurement at one site may not reflect the density at other sites. The value of these techniques in screening the general population for osteoporosis remains to be demonstrated. They are valuable when used to monitor patients longitudinally to assess the progression of disease and the effects of specific therapeutic regimens. There is no established effective therapy for osteoporosis so prevention is the goal. The effectiveness of different programs of physical activity in preventing bone loss and fractures is unknown but isotonic exercises three times a week for thirty minutes is recommended. There is general agreement that adequate calcium intake is important for maintenance of skeletal integrity, but there is no proof that a high dietary calcium alone will prevent osteoporosis. Estrogen therapy clearly prevents the accelerated bone loss which occurs in all white women at the time of menopause, but the question still remains who should be started on estrogens, and within what period of time after menopause are estrogens still useful in preventing postmenopausal bone loss, and for how long do we continue hormone therapy. Many questions are left to be answered but at least now osteoporosis is recognized as a major medical problem and much research is being done to answer the above questions.     

Postmenopausal osteoporosis. Early diagnosis as an indication for preventive hormone therapy

Idiopathic osteoporosis mainly affects postmenopausal women. The normal trabecular volume of the lumbar vertebrae in a sample of healthy perimenopausal women was established by monoenergetic computed tomography. Early diagnosis of diminished bone mass is crucial for the identification of women at risk for involuntary osteoporosis following climacteric estrogen depletion. Body weight, endogenous levels of sex steroids, renal calcium and hydroxyproline excretions are not related to individual bone mass in the lumbar spine.     

激素替代治疗与绝经后骨质疏松症

绝经后骨质疏松症主要是由于卵巢功能的减退或衰竭、雌激素水平下降而导致破骨细胞的骨吸收大于成骨细胞的骨形成,以进行性骨丢失、骨小梁退行性病变、骨质疏松、骨脆性增加和骨折风险增加为临床特征的全身性疾病,具有发病率随绝经年限延长而增高的特点。临床中相当数量的绝经后女性并不重视骨质疏松的严重性,从而延误了预防和治疗的最佳时机,增加了骨质疏松症治疗的复杂性。激素替代治疗是预防和治疗绝经后女性骨质疏松的有效方法之一,尤其是对于预防过早绝经妇女的骨质丢失已成为一线的治疗手段,且具有成本低、安全性高的优点。激素替代治疗不仅可增加患者的骨密度、减缓骨丢失,而且还可使血清降钙素、碱性磷酸酶骨质破坏的标志物较基础水平明显下降,起到预防和治疗绝经后妇女骨质疏松和骨折的作用。本文就绝经后妇女骨质的改变进行综述。     

Trabecular bone density and menstrual function in women runners

Osteoporosis results in decreased bone mineral mass and reduced trabecular bone density. Although its etiology remains unknown, studies have revealed differential changes in the bone mineral densities of postmenopausal women, anorexic women, and amenorrheic female athletes. Correlations have also been made between estrogen deficiency and osteoporosis in both premenopausal and postmenopausal women. In order to examine the possibility of osteopenia, a group of 36 female runners between the ages of 15 and 44 years were evaluated for bone mineral density, menstrual function, and dietary habits. Serum calcium, phosphorus, and parathyroid hormone (PTH) levels were also determined for each participant, as were complete blood counts. Using dual photon absorptiometry, all participants underwent a 20 minute scan of the lumbar spine with specificity to the L1-14 vertebrae. The 36 subjects included 19 oligomenorrheic and 17 eumenorrheic women. Results of bone density analyses revealed that the oligomenorrheic runners had significantly lower calibrated bone mineral density (CBMD) than their eumenorrheic counterparts (P less than or equal to 0.01). Likewise, the PTH levels of the oligomenorrheic runners were also significantly lower (P less than or equal to 0.01). Analysis of dietary logs revealed no significant differences between the dietary habits, the calcium intake, or the caloric intake of the two groups. The data from this study indicate that there is a relationship between reduced serum PTH levels and the oligomenorrheic state. The loss of the protective effect of estrogen in the oligomenorrheic runners possibly contributed to their reduced bone mineral densities and could be a contributing factor in osteopenia.     

Osteoporosis: What Is the Role of Exercise?

Research has not yet identified the best combination of estrogen replacement, calcium, and exercise for fighting osteoporosis. But clinical experience shows that all three are needed to prevent the rapid bone loss that can occur in postmenopausal women.     

Beyond hypoestrogenism in amenorrheic athletes: Energy deficiency as a contributing factor for bone loss

The etiology of amenorrhea in exercising women is linked to a mismatch between caloric intake and high levels of exercise energy expenditure that results in a chronic energy deficit. This in turn stimulates compensatory mechanisms such as weight loss, metabolic hormone alterations, or energy conservation that subsequently causes a central suppression of reproductive function and concomitant hypoestrogenism. This suppression of reproductive function is associated with stress fractures, loss of bone mineral density, the failure to achieve peak bone mass, osteopenia, and osteoporosis. It has generally been accepted that the chronic hypoestrogenism is the major cause of bone loss in exercising women. However, the effects of food restriction and energy deficiency on bone mineral density likely represents an estrogen-independent mechanism for bone loss that involves some of the metabolic-related hormones altered with exercise-associated amenorrhea. These hormones (IGF-1 and leptin) play an important role in modulating bone turnover and bone mineral density in these women.     

Age-, sex-, and menopause-related changes of vertebral and peripheral bone: population study using dual and single photon absorptiometry and radiogrammetry

Vertebral and peripheral bone mass have been measured with single and dual photon absorptiometry and radiogrammetry in 146 male and 220 female volunteers ranging in age from 20 to 85 yr. One hundred four subjects with interfering diseases, treatment, or x-ray manifestations of lumbar osteoarthritis were excluded for purposes of this study. Patterns of age-related bone gain and diminution differed between sexes and measuring sites. The effect of menopause on the peripheral and vertebral skeleton also differed. Men, at all measured sites, have more bone than women. In the fifth decade, however, women's lumbar bone mineral content was almost equal to the value found in men. Bone loss associated with aging was more marked in women than in men and started, for the lumbar spine, at about the age of 25 yr in both women and men and, for the peripheral bones, at the age of 55 in women and 65 in men. Bone loss in the spine in women was not linear. Women in the fifth and sixth decade, who still had menstruation, differed significantly from those who had not menstruated for at least the last 6 mo. Bone diminution at menopause was twice as great in the lumbar spine than elsewhere in the peripheral skeleton, 15% versus 7%. Of the 25% total bone loss of the spine during adult life in women, 60% was lost within 10 yr after menopause. Estrogen deficiency, not aging, is the predominant cause of bone loss in the spine. For the peripheral skeleton, there is a two-component decrease, a rapid loss induced by the menopause superimposed on a slower age-related loss. Although there was a significant correlation between peripheral and vertebral bone mass indices, it was clear that observations made at one site will not necessarily reflect changes observed at another site.     

Bone densitometry as a screening tool for osteoporosis in postmenopausal women

This report provides general information about osteoporosis and describes the use of bone densitometry as a tool to screen for, diagnose and manage osteoporosis in white postmenopausal women. Discussion is limited to white women because of lack of research on osteoporosis in men, and in women of different racial and ethnic groups. The report does not evaluate the safety and efficacy of all bone densitometry devices, but focuses on the two diffusing most rapidly in Minnesota--dual x-ray absorptiometry (DXA or DEXA) and quantitative computed tomography (QCT). Osteoporosis is a degenerative bone disease that affects approximately 24 million Americans. Of that number 33 percent are post-menopausal women who have decreased bone density due to lowered estrogen levels. Because the estimated cost of osteoporosis-related fractures in the United States is between $8 and $10 billion each year, there is great interest in the diagnosis, prevention and treatment of the disease. Of all related fractures, hip fractures pose the most serious health problem. The incidence of this fracture appears to be increasing, with 250,000 to 300,000 occurring each year Treatment options are limited, if a person's bone mass or density has deteriorated to the point where fractures may occur. Preventive measures should therefore be undertaken by all women early in life to decrease their risk of osteoporosis. Based on available evidence, the HTAC concludes that state-of-the-art bone densitometry is safe and indicated as a diagnostic and treatment aid for postmenopausal women at risk for the disease. However, bone densitometry is not indicated as a broad screening tool for all postmenopausal women, regardless of whether they are at risk for the disease.     

Integrated imaging approach to osteoporosis: state-of-the-art review and update

Osteoporosis is the most common of all metabolic bone disorders. It is characterized by low bone mass and microarchitectural deterioration of bone tissue, with a consequent increase in bone fragility and susceptibility to fractures. Because of the increasing aging of the world population, the number of persons affected by osteoporosis is also increasing. Complications related to osteoporosis can create social and economic burdens. For these reasons, the early diagnosis of osteoporosis is crucial. Conventional radiography allows qualitative and semiquantitative evaluation of osteoporosis, whereas other imaging techniques allow quantification of bone loss (eg, dual-energy x-ray absorptiometry and quantitative computed tomography [CT]), assessment for the presence of fractures (morphometry), and the study of bone properties (ultrasonography). In recent years, new imaging modalities such as micro-CT and high-resolution magnetic resonance imaging have been developed in an attempt to help diagnose osteoporosis in its early stages, thereby reducing social and economic costs and preventing patient suffering. The correct diagnosis of osteoporosis results in better management in terms of prevention and adequate pharmacologic or surgical treatment.     

Bone mineral content in early-postmenopausal and postmenopausal osteoporotic women: comparison of measurement methods

To investigate associations among methods for noninvasive measurement of skeletal bone mass, we studied 40 healthy early postmenopausal women and 68 older postmenopausal women with osteoporosis. Methods included single- and dual-energy quantitative computed tomography (QCT) and dual-photon absorptiometry (DPA) of the lumbar spine, single-photon absorptiometry (SPA) of the distal third of the radius, and combined cortical thickness (CCT) of the second metacarpal shaft. Lateral thoracolumbar radiography was performed, and a spinal fracture index was calculated. There was good correlation between QCT and DPA methods in early postmenopausal women and modest correlation in postmenopausal osteoporotic women. Correlations between spinal measurements (QCT or DPA) and appendicular cortical measurements (SPA or CCT) were modest in healthy women and poor in osteoporotic women. Measurements resulting from one method are not predictive of those by another method for the individual patient. The strongest correlation with severity of vertebral fracture is provided by QCT; the weakest, by SPA. There was a high correlation between single- and dual-energy QCT results, indicating that errors due to vertebral fat are not substantial in these postmenopausal women. Single-energy QCT may be adequate and perhaps preferable for assessing postmenopausal women. The measurement of spinal trabecular bone density by QCT discriminates between osteoporotic women and younger healthy women with more sensitivity than measurements of spinal integral bone by DPA or of appendicular cortical bone by SPA or CCT.     

肾移植术后患者骨密度水平的调查研究

 目的 探讨肾移植术后患者与正常体检人群骨密度(bone mineral density, BMD)水平,以及骨量丢失(骨量减少和骨质疏松)发病率的差异。方法 选择在武警总医院随访的肾移植患者177例(男104例,女73例),根据女性是否绝经和男性年龄将入选者分为＜50岁男性、≥50岁男性、绝经前女性和绝经后女性移植组。选择同期在我院体检的正常人群250例(男131例、女119例)作为对照组。采用双能X线骨密度仪测定所有人的腰椎、右股骨颈和右全髋BMD,比较各移植组与对照组BMD以及骨量丢失发病率的差异。结果 各肾移植组患者股骨颈和全髋骨密度均低于对照组(P<0.01);＜50岁男性肾移植患者腰椎骨密度低于对照组(P<0.01)。男性和绝经后女性移植患者骨量丢失(包括骨量减少和骨质疏松)发病率显著高于对照组(P<0.01)。结论 肾移植患者骨密度水平明显低于正常体检人群,且骨量丢失的发病率高于正常人群。建议肾移植患者术后在维生素D和钙剂的基础上,选用双膦酸盐防治骨质疏松和骨折。     

Rate of spinal trabecular bone loss in normal perimenopausal women: CT measurement

Age-related bone loss in women may begin at any time following attainment of peak skeletal maturity bone mass. The rate of bone loss may accelerate near the time of menopause and continue for several years thereafter. Women with low baseline bone mass and women who are fast bone losers are potentially at risk for early spinal osteoporosis. In a prospective longitudinal study, spinal trabecular bone mineral content (BMC) of 83 healthy women, 47-53 years old, was measured with use of computed tomography (CT) at 0, 12, 24, and 36 months. Fifty-four of these same women had a fifth measurement at 48 months. In 51 women the rate of bone loss was less than or equal to 2% per year (average 1.96%; normal bone losers); in 32, it was more than 2% per year (average 5.61%; fast bone losers). CT studies can identify women with low spinal trabecular BMC and/or fast bone loss--women likely to be at increased risk for early spinal osteoporosis. This information may be useful in selection of candidates for vigorous preventive measures, including estrogen replacement.     

Cyclic oral phosphate and etidronate increase femoral and lumbar bone mineral density and reduce lumbar spine fracture rate over three years.

We have performed a study of the safety and efficacy of cyclic sequential oral phosphate, diphosphonate and calcium carbonate. Forty-two postmenopausal women with osteoporosis diagnosed by dual-photon absorptiometry were treated with a sequential cyclic regimen of oral phosphate for 3 days, etidronate for 2 wk, and then a calcium salt for 12 wk. This was repeated cyclically for 3 yr. They were rescanned after every two 101-day cycles. A control group of 20 patient receiving only the calcium salt was matched for age, time since menopause, race and sex. The group treated with cyclic phosphate, etidronate, and calcium regimen had 80% fewer fractures than the control group over 3 yr of follow-up. Significant response in halting bone mineral loss and increasing bone mineral density was seen in none of the controls but in 90% of treated patients' lumbar spine and 70%-80% of the three regions of the femoral neck examined.     

绝经期女性胸腰椎后凸与椎体压缩骨折相关性分析

目的探讨绝经期女性骨质疏松骨折的临床特点,以及胸腰段脊柱力线对骨折发生的风险分析。方法本研究为病例对照研究,收集自2013年1月至2015年6月因骨质疏松性压缩骨折在北京积水潭医院住院,并行椎体成形术的绝经期女性患者396例(研究组),平均年龄64岁(55~72岁);对照组选取因下腰椎退行性疾病住院手术的患者271例,平均年龄62岁(55~84岁)。记录所有患者入院时的年龄、体质量指数(BMI)、骨密度定量CT(QCT)、骨折椎体。利用站立位X线影像测量胸腰段(T11~L2)矢状位和冠状位的Cobb角。利用患者胸腰段椎体的平均Cobb角,修订并推算骨折前患者T11~L2的矢状位和冠状位Cobb角。分析胸腰段骨质疏松性骨折的临床点和危险因素。结果研究组患者中,T11椎体骨折患者69例(19.6%),T12椎体骨折153例(43.5%),L1椎体骨折174例(49.4%),L2椎体骨折70例(19.9%)。研究组和对照组患者的年龄和BMI差异无统计学意义(P>0.05)。研究组患者修订后的胸腰段矢状位Cobb角为(13.6°±7.6°),对照组为(5.9°±6.0°),两组间差异有统计学意义(P<0.01)。研究组患者修订后胸腰段冠状位Cobb角为(0.4°±4.0°),对照组为(0.1°±4.1°),两组间差异无统计学意义(P>0.05)。使用ROC曲线和尤登指数计算胸腰段矢状位Cobb角,对于胸腰椎骨质疏松性骨折的最佳分界值为7.5°,OR值为7.6(95%可信区间为2.5~22.8)。结论胸腰段矢状位后凸会增加骨质疏松性骨折的风险,后凸Cobb角度>7.5°时,骨折风险增加7倍,但冠状位的侧弯不增加骨折的风险。     

Validation of dental panoramic radiography measures for identifying postmenopausal women with spinal osteoporosis

OBJECTIVE: Measurements of mandibular inferior cortical shape and width detected on dental panoramic radiographs may be a useful screening tool for spinal osteoporosis in postmenopausal women. The purposes of this study were to clarify whether these measures are validated compared with simple screening tools based on questionnaires, such as the osteoporosis self-assessment tool (OST) and whether these measures can be used in postmenopausal women with histories of hysterectomy, oophorectomy, or estrogen use. SUBJECTS AND METHODS: We calculated the diagnostic performances of panoramic measurements and the OST for identifying women with spinal osteoporosis in both 159 healthy postmenopausal and 157 postmenopausal women with histories of hysterectomy, oophorectomy, or estrogen use. Spinal osteoporosis was defined as a bone mineral density T score of -2.5 or less at the lumbar spine. Cortical shape and width were evaluated on dental panoramic radiographs. Receiver operating characteristic curve analyses were used to determine the optimal cutoff thresholds for cortical width and the OST in healthy postmenopausal women. RESULTS: The sensitivity and specificity, respectively, for identifying women with spinal osteoporosis were 89.5% and 33.9% for cortical width, 86.8% and 57.8% for the OST, and 86.8% and 63.6% for cortical shape in healthy postmenopausal women. Sensitivity and specificity, respectively, were 92.5% and 35.0% for cortical width, 72.5% and 58.1% for the OST, and 80.0% and 64.1% for cortical shape in postmenopausal women with histories of hysterectomy, oophorectomy, or estrogen use. CONCLUSION: Dentists may be able to refer postmenopausal women with suspected spinal osteoporosis for bone densitometry on the basis of dental panoramic radiographs with diagnostic performance similar to that of osteoporosis screening tools based on questionnaires.     

Bone health across the lifespan--exercising our options

Exercise is frequently extolled as an osteoporosis treatment. In reality, the use of exercise as an osteoporosis intervention lies more in its ability to: 1) maximize peak bone mass attained in youth; 2) maintain bone mass or reduce age-related bone loss; and 3) preserve muscle strength and postural stability to reduce the risk of falling and fracturing in the later years.     

Skeletal effects of menstrual disturbances in athletes

This article reviews the skeletal effects and clinical implications of menstrual disturbances in active women. At the lumbar spine, menstrual disturbances are associated with premature bone loss or failure to reach peak bone mass, while appendicular sites are less affected. This suggests that trabecular bone is more sensitive to hormonal stimuli and less responsive to mechanical loading than cortical bone. Although the mechanisms responsible for the detrimental effects of menstrual disturbances are likely to be multifactorial, low circulating levels of oestrogen are thought to be the main cause. The clinical significance of menstrual disturbances depends upon a number of factors, including type of sport, genetic back-ground, body composition and calcium intake. Not all athletes who present with menstrual disturbances will develop osteopenia. Nevertheless, the risk of stress fracture does seem to be increased in athletes with menstrual disturbances and with lower bone density. Whether athletes with menstrual disturbances are at a greater risk for osteoporosis in later life is not yet known. Bone loss can be at least partially reversed, especially with the spontaneous resumption of menses. This may serve to offset any previous increased risk of osteoporsis. Furthermore, other factors, apart from low bone mass, act to determine the likelihood of osteoporotic fractures. Therefore, the clinical significance of menstrual disturbances associated with exercise participation needs to be established for each individual athlete. Bone densitometry may guide the clinician in this respect and assist in the formulation of appropriat management strategies.