Effects of exercise and amenorrhea on bone mineral density in teenage runners

Position Statement: Exercise Guidelines to Increase Peak Bone Mass in Adolescents

Background

An increase in bone mineral density during adolescence increases resistance to fractures in older age. The Korean Society for Bone and Mineral Research and the Korean Society of Exercise Physiology developed exercise guidelines to increase the peak bone mass (PBM) in adolescents based on evidence through a systematic review of previous research.

Methods

Articles were selected using the systematic method, and the exercise guidelines were established by selecting key questions (KQs) and defining the effects of exercises based on evidence through a literature review for selecting the final exercise method. There were 9 KQs. An online search was conducted on articles published since 2000, and 93 articles were identified.

Results

An increase in PBM in adolescence was effective for preventing osteoporosis and fractures in older age. Exercise programs as part of vigorous physical activity (VPA) including resistance and impact exercise at least 5 to 6 months were effective for improving PBM in adolescents. It is recommended that resistance exercise is performed 10 to 12 rep·set⁻¹ 1-2 set·region⁻¹ and 3 days·week⁻¹ using the large muscles. For impact exercises such as jumping, it is recommended that the exercise is performed at least 50 jumps·min⁻¹, 10 min·day⁻¹ and 2 days·week⁻¹.

Conclusions

Exercise guidelines were successfully developed, and they recommend at least 5 to 6 months of VPA, which includes both resistance and impact exercises. With the development of exercise guidelines, the incidence of osteoporosis and fractures in the aging society can be reduced in the future, thus contributing to improved public health.

Obstacles in the optimization of bone health outcomes in the female athlete triad

Maintaining low body weight for the sake of performance and aesthetic purposes is a common feature among young girls and women who exercise on a regular basis, including elite, college and high-school athletes, members of fitness centres, and recreational exercisers. High energy expenditure without adequate compensation in energy intake leads to an energy deficiency, which may ultimately affect reproductive function and bone health. The combination of low energy availability, menstrual disturbances and low bone mineral density is referred to as the 'female athlete triad'. Not all athletes seek medical assistance in response to the absence of menstruation for 3 or more months as some believe that long-term amenorrhoea is not harmful. Indeed, many women may not seek medical attention until they sustain a stress fracture. This review investigates current issues, controversies and strategies in the clinical management of bone health concerns related to the female athlete triad. Current recommendations focus on either increasing energy intake or decreasing energy expenditure, as this approach remains the most efficient strategy to prevent further bone health complications. However, convincing the athlete to increase energy availability can be extremely challenging. Oral contraceptive therapy seems to be a common strategy chosen by many physicians to address bone health issues in young women with amenorrhoea, although there is little evidence that this strategy improves bone mineral density in this population. Assessment of bone health itself is difficult due to the limitations of dual-energy X-ray absorptiometry (DXA) to estimate bone strength. Understanding how bone strength is affected by low energy availability, weight gain and resumption of menses requires further investigations using 3-dimensional bone imaging techniques in order to improve the clinical management of the female athlete triad.

The presence of both an energy deficiency and estrogen deficiency exacerbate alterations of bone metabolism in exercising women

BACKGROUND

Bone loss in amenorrheic athletes has been attributed to energy deficiency-related suppression of bone formation, but not increased resorption despite hypoestrogenism.

OBJECTIVE

To assess the independent and combined effects of energy deficiency and estrogen deficiency on bone turnover markers in exercising women.

DESIGN

PINP, osteocalcin, U-CTX-I, TT3, leptin, and ghrelin were measured repeatedly, and bone mineral density (BMD) was measured once in 44 exercising women. Resting energy expenditure (REE) was used to determine energy status (deficient or replete) and was corroborated with measures of metabolic hormones. Daily levels of urinary estrone and pregnanediol glucuronides (E1G, PdG), were assessed to determine menstrual and estrogen status. Volunteers were then retrospectively categorized into 4 groups: 1) Energy Replete+Estrogen Replete (EnR+E2R), (n=22), 2) Energy Replete+Estrogen Deficient (EnR+E2D), (n=7), 3) Energy Deficient+Estrogen Replete (EnD+E2R), (n=7), and 4) Energy Deficient+Estrogen Deficient (EnD+E2D), (n=8).

RESULTS

The groups were similar (p>0.05) with respect to age (24.05+/-1.75 yrs), weight (57.7+/-2.2 kg), and BMI (21.05+/-0.7 kg/m2). By design, REE/FFM (p=0.028) and REE:pREE (p<0.001) were lower in the EnD vs. EnR group, and the E2D group had a lower REE:pREE (p=0.005) compared to the E2R group. The EnD+E2D group had suppressed PINP (p=0.034), and elevated U-CTX-I (p=0.052) and ghrelin (p=0.028) levels compared to the other groups. These same women also had convincing evidence of energy conservation, including TT3 levels that were 29% lower (p=0.057) and ghrelin levels that were 44% higher (p=0.028) than that observed in the other groups. Energy deficiency was associated with suppressed osteocalcin, and TT3 (p<0.05), whereas estrogen deficiency was associated with decreased E1G (p<0.02), and lower L2-L4 BMD (p=0.033). Leptin was significant in predicting markers of bone formation, but not markers of bone resorption.

CONCLUSIONS

When the energy status of exercising women was adequate (replete), there were no apparent perturbations of bone formation or resorption, regardless of estrogen status. Estrogen deficiency in exercising women, in the presence of an energy deficiency, was associated with bone loss and involved suppressed bone formation and increased bone resorption. These findings underscore the importance of avoiding energy deficiency, which is associated with hypoestrogenism, to avoid bone health problems.

Menstrual disorders in athletes

The various menstrual disorders in athletes may reflect different degrees of exposure to a disrupting factor or differences in the susceptibility of various women to disruption. The incidences of these disorders are not well documented, but they appear to be highest in aesthetic, endurance and weight-class sports, and at younger ages, higher training volumes and lower bodyweights. The morbid effects of these disorders include infertility, low bone mass, impaired endothelium-dependent vasodilation, and impaired skeletal muscle oxidative metabolism. The high incidences of menstrual disorders in athletes may derive in part from the self-selection of extraneously affected women into athletics, but many women acquire their menstrual disorders in athletics by failing to adequately increase dietary energy intake in compensation for exercise energy expenditure. Applied research is needed to develop effective dietary interventions that are acceptable to athletes.

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.

Dose-response relationships between energy availability and bone turnover in young exercising women

To help refine nutritional guidelines for military servicewomen, we assessed bone turnover after manipulating the energy availability of 29 young women. Bone formation was impaired by less severe restrictions than that which increased bone resorption. Military servicewomen and others may need to improve their nutrition to avoid these effects.

INTRODUCTION

We determined the dose-response relationship between energy availability (defined as dietary energy intake minus exercise energy expenditure) and selected markers of bone turnover in 29 regularly menstruating, habitually sedentary, young women of normal body composition.

MATERIALS AND METHODS

For 5 days in the early follicular phase of two menstrual cycles separated by at least 2 months, subjects expended 15 kcal/kgLBM/day in supervised exercise at 70% of aerobic capacity and consumed controlled amounts of a clinical dietary product in balanced (45 kcal/kgLBM/day) and one of three restricted (either 10, 20, or 30 kcal/kgLBM/day) energy availability treatments in random order. Blood was sampled at 10-minute intervals, and urine was collected for 24 h. Samples were assayed for plasma osteocalcin (OC), serum type I procollagen carboxy-terminal propeptide (PICP), and urinary N-telopeptide (NTX).

RESULTS

NTX concentrations (p < 0.01) and indices of bone resorption/formation uncoupling (Z(NTX-OC) and Z(NTX-PICP); both p < 10(-4)) were increased by the 10 kcal/kgLBM/day treatment. OC and PICP concentrations were suppressed by all restricted energy availability treatments (all p < 0.05). PICP declined linearly (p < 10(-6)) with energy availability, whereas most of the suppression of OC occurred abruptly between 20 and 30 kcal/kgLBM/day (p < 0.05).

CONCLUSIONS

These dose-response relationships closely resembled those of particular reproductive and metabolic hormones found in the same experiment and reported previously: similar relationships were observed for NTX and estradiol; for PICP and insulin; and for OC, triiodothyronine (T3), and insulin-like growth factor (IGF)-I. The uncoupling of bone resorption and formation by severely restricted energy availability, if left to continue, may lead to irreversible reductions in BMD, and the suppression of bone formation by less severe restrictions may prevent young women from achieving their genetic potential for peak bone mass. More prolonged experiments are needed to determine the dose-response relationships between chronic restrictions of energy availability and bone turnover.

Effects of aging and postmenopausal hypoestrogenism on skin elasticity and bone mineral density in Japanese women

Skin collagen content and bone mass decrease with aging. Loss of collagen from the skin might decrease its elasticity. We investigated associations between skin elasticity, bone mineral density (BMD), age, and menopausal hypoestrogenism. Thirty-eight healthy Japanese postmenopausal women were studied (mean age, 55.7 +/- 5.9 yr; range, 48 to 71). Skin elasticity was measured using a suction device applied to the dorsal right forearm. BMD values of L2 to 4 vertebral bodies were measured by dual-energy X-ray absorptiometry. Age showed significant negative correlations with both skin elasticity and BMD (r = -0.57, p<0.001 and r = -0.40, p<0.05, respectively). Years since menopause also showed significant negative correlations with both skin elasticity and BMD (r = -0.51, p<0.01 and r = -0.41, p<0.05, respectively). We also found a positive correlation between skin elasticity and BMD in these postmenopausal women (r = 0.44, p<0.01). In conclusion, we demonstrated declining skin elasticity and bone mass in postmenopausal women to possibly be age- and estrogen-related. Additionally, decreased skin elasticity might serve as a predictor of bone loss in postmenopausal women.

The assessment of bone metabolism in female elite endurance athletes by biochemical bone markers

Purpose: Premature osteoporosis is a frequent problem in female athletes. Current concepts suggest that a disruption of the hypothalamic-pituitary axis leads to hypoestrogenism, which then causes amenorrhea and osteoporosis. However, the underlying mechanisms have been insufficiently investigated. Osteoprotegerin (OPG) and soluble TNF-α receptor antagonist ligand (sRANKL) regulate the balance of osteoblasts and osteoclasts. Their role in the pathogenesis of osteoporosis in female athletes has not been studied yet.

Methods: We measured OPG and sRANKL in relation to biochemical bone markers [osteocalcin (OC), bone alkaline phosphatase (BAP), serum β-crosslaps (CTx)] and female sex hormones [estradiol (E2) and luteinizing hormone (LH)] in fastening blood samples from 25 female elite endurance athletes and 25 matched controls.

Results: Athletes exhibited significantly higher levels of the bone resorption marker CTx than controls (0.61±0.26 vs. 0.44±0.15ng/ml). OPG and sRANKL were not changed. Subgroup analysis revealed that athletes using oral contraceptives [A-OCC(−)] had significantly higher levels of CTx (0.82±0.20 vs. 0.50±0.14ng/ml), BAP [37.3 (23.2–54.4) U/l vs. 25.2 (20.3–35.6) U/l] and OPG (3.4±0.8 vs. 2.7±0.8ng/ml) than controls who did not use oral contraceptives [C-OCC(−)]. While the difference for CTx exceeded the least significant change in this marker by approximately 30%, the differences for the bone formation markers OC and BAP were close to the least significant change. In athletes using oral contraceptives [A-OCC(+)] we found no differences compared to controls.

Conclusions: A-OCC(−) athletes have increased bone turnover with a particular stimulation of bone resorption. The increased bone resorption is not accompanied by a shift of the OPG/sRANKL relationship towards an osteoclastogenic constellation. Since increased bone resorption was not detectable in A-OCC(+) athletes, it can be suggested that OCC use might protect bone health in female athletes.

Persistent osteopenia in ballet dancers with amenorrhea and delayed menarche despite hormone therapy: a longitudinal study

OBJECTIVE

To investigate the role of estrogen deprivation and replacement in amenorrheic and nonamenorrheic dancers on hormone therapy and calcium.

DESIGN

Clinical, placebo-controlled, randomized trial study.Healthy volunteers in an academic research environment.

PATIENT(S)

Fifty-five dancers (mean age: 22.0 +/- 4.6, age at menarche: 14.7 +/- 2.3 years), including 24 amenorrheics.

INTERVENTION(S)

Amenorrheics were randomized in a controlled trial to receive placebo or Premarin, 0.625 mg for 25 days monthly, with Provera, 10 mg, for 10 of these 25 days (hormone therapy) for 2 years. These women were compared to normally menstruating controls. The study participants also received 1250 mg of calcium per day.

MAIN OUTCOME MEASURE(S)

Bone mineral density (BMD) measured at the foot, wrist, and lumbar spine. Our overall results showed no difference in BMD between the treated or placebo groups, indicating that hormone therapy did not change or normalize BMD when compared to normals. Five patients (all on placebo) who resumed menses during the study showed an increase in BMD without normalization.

CONCLUSION(S)

These findings suggest that mechanisms other than hypoestrogenism may be involved with the osteopenia associated with exercise-induced amenorrhea.

Physiological factors associated with low bone mineral density in female endurance runners

OBJECTIVE

To explore potential factors that could be associated with low bone mineral density (BMD) in female endurance runners.

METHODS

Fifty two female endurance runners (1,500 m to marathon), aged 18-44 years, took part. Body fat percentage, lumbar spine BMD, and femoral neck BMD were measured using the Hologic QDR 4,500w bone densitometer. Data on training, menstrual cycle status, osteoporosis, and health related factors were obtained by questionnaire. Dietary variables were assessed from a prospective seven day dietary record of macronutrients and micronutrients.

RESULTS

The mean (SD) lumbar spine and femoral neck BMD were 1.11 (0.11) and 0.89 (0.12) g/cm(2) respectively. A backward elimination regression analysis showed that age, body mass, body fat, distance run, magnesium, and zinc intake were the variables significantly associated with BMD. Lumbar spine BMD (g/cm(2)) = -1.90 + (0.0486 x age (years)) + (0.342 x log mass (kg)) - (0.000861 x age(2) (years)) - (0.00128 x distance (km/week)), with an R(2) = 30.1% (SEE = 0.089 (95% confidence interval (CI) 0.05 to 0.23); p<0.001). Femoral neck BMD (g/cm(2)) = -2.51 - (0.00989 x age (years)) + (0.720 x log mass (kg)) + (0.000951 x magnesium (mg/day)) -(0.0289 x zinc (mg/day)) - (0.00821 x body fat (%)) - (0.00226 x distance (km/week)), with an R(2) = 50.2% (SEE = 0.100 (95% CI 0.06 to 0.22); p<0.001). The negative association between skeletal BMD and distance run suggested that participants who ran longer distances had a lower BMD of the lumbar spine and femoral neck. Further, the results indicated a positive association between body mass and BMD, and a negative association between body fat and BMD.

CONCLUSIONS

The results suggest a negative association between endurance running distance and lumbar spine and femoral neck BMD, with a positive association between body mass and femoral neck and lumbar spine BMD. However, longitudinal studies are required to assess directly the effect of endurance running and body mass on BMD, and to see if the addition of alternative exercise that would increase lean body mass would have a positive effect on BMD and therefore help to prevent osteoporosis.

Evaluating and treating exercise-related menstrual irregularities

Menstrual abnormalities, from a few skipped periods to a complete absence of menses, are extremely common in both athletic and nonathletic adolescents and women in their early 20s. Exercise-related menstrual abnormality is linked with hypothalamic pituitary axis dysfunction and is a diagnosis of exclusion. In athletes, treatment of secondary menstrual abnormalities and associated health concerns, such as bone density, may include medication and restriction from activity.

Estrogen replacement therapy and female athletes: current issues

Physicians commonly recommend estrogen replacement as treatment for exercise-associated amenorrhoea. While the evidence shows that the basis of the amenorrhoea is estrogen deficiency, it is not clear that it is the only factor in the development of lowered bone density found in oligo-amenorrhoeic female athletes. Nutritional factors, significant in the development of the reproductive dysfunction, could also contribute to bone loss. No randomised, controlled studies of estrogen replacement in athletes have been published. However, one nonrandomised study of a small group of athletes does suggest that there are significant gains in bone density to be made by the initiation of estrogen therapy. More research is clearly needed.

The physiology of the highly trained female endurance runner

Continuing improvements in the performance of female endurance runners and increasing levels of participation have generated the need to know more about the physiology of this group. Specific research is needed in this area, as data referring to male endurance runners cannot legitimately be applied to the female endurance runner because of their markedly different physiological and hormonal profiles. Recent developments in our understanding of an athlete's physiology (mainly in relation to the male endurance runner) have revealed new areas of interest that need to be assessed with specific reference to the female athlete. Relatively little attention has been directed towards identifying the major physiological characteristics of the highly trained/elite female endurance runner in general, and that which has been published on such factors and the effects of the menstrual cycle have produced equivocal results. Moreover, the impact of such training upon the menstrual cycle and endurance running performance is a controversial area, especially when assessing its subsequent impact on health-related issues. Reports of the condition referred to as the 'female athlete triad' have increased in recent years, with a decrease in bone mineral density predisposing the female athlete to increased risks of stress fractures. The aetiology of this triad is multifactorial, with such risk factors including nutrition, menstrual status, training intensity and frequency, body size and composition and psychology/physical stress. However, research limitations and flaws have lead to controversy in the literature regarding the immediate and long term effects of the triad on the female athlete. Likewise, the effects of the oral contraceptive pill on health and endurance performance also remain elusive, with a dearth of research pertaining to how oral contraceptive agents can aid athletic performance and the long term health of the female athlete. The purpose of this paper is to critically appraise the existing literature to provide a current review of the physiological scientific knowledge base in relation to the female athlete, health, training and performance, with suggestions for future areas of research. It is well known that certain menstrual and health-related performance factors of the female athlete, that is, physiological predictors of performance and body fat, have been extensively investigated over the last 30 years. However, a variety of methodological flaws and inconsistencies are present within the research and thus only the most prominent and well controlled studies within this area over the past 30 years will be referred to.

Bone turnover in amenorrhoeic and eumenorrhoeic women distance runners

Bone remodelling has not been assessed in women distance runners with chronic amenorrhoea. The purpose of this study was to compare indices of bone turnover and energy balance in runners with chronic amenorrhoea, runners with a history of regular menstrual cycles and sedentary controls. Subjects comprised 3 groups of 9 women, matched for age [mean+/-SEM: 27.2+/-1.8 yrs] and categorised as amenorrhoeic runners (AmR), eumenorrhoeic runners (EuR) and eumenorrhoeic sedentary controls (SC). Serum concentrations of bone formation markers [osteocalcin (OC), carboxy-terminal propeptide of type 1 collagen (P1CP), bone alkaline phosphatase (BAP)], E2, total T3 and IGF-1 were measured from a fasting morning blood sample. Urine levels of bone resorption markers [pyridinoline (Pyr) and deoxypyridinoline (Dpyr)] were measured and corrected for creatinine excretion. Mean daily energy balance (EB) was calculated by subtracting dietary energy intake (EI) from energy expenditure (EE) estimated from reported activity patterns over 7 days. The results showed that all bone turnover markers were lower in AmR than in EuR or SC (P<0.001: OC, BAP and P1CP; P<0.05: Pyr and Dpyr). Furthermore, when z-scores for each bone marker in runners were calculated against mean values for SC (by subtracting each measure of bone turnover from the mean value for SC and expressing the difference as a fraction of the SD of this mean value), bone resorption appeared to outweigh formation in AmR, but not in EuR. Serum concentrations of E2, T3 and IGF-1 were also lower in AmR than in EuR or SC (P<0.001: all hormones), as was EB (P<0.001). These findings suggested that in AmR there was some factor which was reducing bone turnover and in particular, bone formation. This factor might have been linked to an energy deficit and the effects of this deficit on body mass, body composition and metabolism.