Factors that influence peak bone mass formation: a study of calcium balance and the inheritance of bone mass in adolescent females

Weight-bearing exercise and markers of bone turnover in female athletes

Weight-bearing activity provides an osteogenic stimulus, while effects of swimming on bone are unclear. We evaluated bone mineral density (BMD) and markers of bone turnover in female athletes (n = 41, age 20.7 yr) comparing three impact groups, high impact (High, basketball and volleyball, n = 14), medium impact (Med, soccer and track, n = 13), and nonimpact (Non, swimming, n = 7), with sedentary age-matched controls (Con, n = 7). BMD was assessed by dual-energy X-ray absorptiometry at the lumbar spine, femoral neck (FN), Ward's triangle, and trochanter (TR); bone resorption estimated from urinary cross-linked N-telopeptides (NTx); and bone formation determined from serum osteocalcin. Adjusted BMD (g/cm; covariates: body mass index, weight, and calcium and calorie intake) was greater at the FN and TR in the High group (1.27 +/- 0.03 and 1.05 +/- 0.03) than in the Non (1.05 +/- 0.04 and 0.86 +/- 0.04) and Con (1.03 +/- 0.05 and 0.85 +/- 0.05) groups and greater at the TR in the Med group (1.01 +/- 0.03) than in the Non (0.86 +/- 0.04) and Con (0.85 +/- 0.05) groups. Total body BMD was higher in the High group (4.9 +/- 0.12) than in the Med (4.5 +/- 0.12), Non (4.2 +/- 0.14), and Con (4.1 +/- 0.17) groups and greater in the Med group than in the Non and Con groups. Bone formation was lower in the Non group (19.8 +/- 2.6) than in the High (30.6 +/- 3.0) and Med (32.9 +/- 1.9, P < or = 0.05) groups. No differences in a marker of bone resorption (NTx) were noted. This indicates that women who participate in impact sports such as volleyball and basketball had higher BMDs and bone formation values than female swimmers.

Marginal vitamin and mineral intake of Costa Rican adolescents

BACKGROUND

Although a great deal of attention is given to macronutrient and energy intake in the diet, elements essential to dietary metabolic balance include important micronutrients. Very little information exists on vitamin and mineral intake during adolescence, especially in developing countries.

METHODS

The micronutrient intake of urban and rural adolescents aged 12-19 years from the Costa Rican capital city, San José, was evaluated. Prospective 3-day diet records including 2 weekdays and 1 weekend day were used for dietary data. We evaluated the micronutrient intake to determine the nutrient adequacy ratio.

RESULTS

Approximately 30% of adolescents did not meet the 70% level of the daily recommended intake (DRI) for vitamin Bl2. Additionally, 40% of the Costa Rican youngsters presented a vitamin A, E, and iron intake of between 30 and 69% of the DRI or recommended daily dose (RDA) for these nutrients. Likewise, approximately 15% of adolescents did not meet 30% of the DRI or RDA indicators for these nutrients. The micronutrients most at risk for inadequate intake were zinc, calcium, magnesium, and folate: more than 25% of the adolescents did not meet 50% of DRI or RDA indications for these micronutrients. Contrariwise, vitamin C, vitamin B6, thiamin, riboflavin, and niacin were the nutrients less at risk for inadequate intake. Fast foods prepared in school cafeterias provided approximately 15-30% of the DRI for vitamins B1, B2, B6, Bl2, and niacin, approximately 18% of the RDA for iron, and over 40% of the RDA for vitamin E.

CONCLUSIONS

Nutritional interventions and educational strategies are needed to promote the adoption of healthful eating habits among adolescents.

Bone loss in adolescents using Depo-Provera

ISSUES AND PURPOSE

Contraceptive methods that decrease bone density in a population already deficient in calcium are a rising concern in women's health.

CONCLUSIONS

Use of Depo-Provera (DMPA) significantly decreases bone mass density (BMD) in normal adolescents up to the age of 21. DMPA is often used in adolescents with disabilities who may already be at high risk for osteoporosis. The effects are likely to be similar to that in able-bodied adolescents, but research is limited.

PRACTICE IMPLICATIONS

Through early identification of risk factors in able-bodied and disabled adolescents, primary care providers considering the use of DMPA in adolescents can optimize BMD by providing adequate nutritional assessment, counseling on nutritional sources of calcium, calcium supplementation, guidance on exercise, and alcohol and smoking prevention or cessation.

Increasing weight-bearing physical activity and calcium intake for bone mass growth in children and adolescents: a review of intervention trials

OBJECTIVE

The purpose of this review is to evaluate the current state-of-the-science for interventions to increase bone mass gains in children and adolescents using weight-bearing physical activity or calcium supplementation.

METHODS

Studies were located using computerized and manual searches of the empirical literature. Inclusion criteria were: (a) intervention study targeting weight-bearing physical activity or calcium intake; (b) inclusion of a control group; (c) subject age range under 18 years; and (d) outcome measured bone mineral density or bone mineral content.

RESULTS

Weight-bearing physical activity and calcium supplement intervention studies both consistently show positive effects on bone mass gains in children and adolescents. The most consistent findings for both weight-bearing physical activity and calcium were for lumbar spine and total body bone sites. Only weight-bearing physical activity interventions had significant effects on the femoral neck sites. Low power may have contributed to the lack of statistically significant findings in several studies and also prevented proper evaluation of potential interactions between pubertal status and interventions on bone mass gains.

CONCLUSIONS

Increases in weight-bearing physical activity or calcium intake have positive effects on bone mass gains in children and adolescents. Further research is needed to evaluate: (a) the long-term durability of these effects; (b) specific dose-response associations; (c) interactions between weight-bearing physical activity and calcium intake; and (d) interactions between pubertal development and weight-bearing physical activity or calcium intake on bone mass outcomes.

Associations between maternal peak bone mass and bone mass in prepubertal male and female children

The aim of this study was to estimate heritability of bone density in premenopausal women, prepubertal male, and prepubertal female child pairs. We studied 291 pairs (mothers, mean age, 33 years, range 22-45 years; children, mean age, 7.92 years, range 7.32-8.92 years). Bone density and body composition were assessed by dual-energy X-ray absorptiometry. Height and weight were measured in both mother and child. Body size-adjusted heritability estimates for areal bone density (g/cm2) were all statistically significant (femoral neck, 59%; lumbar spine, 38%; total body, 41%) and were consistently and significantly higher in mother-daughter pairs (n = 105) as compared with mother-son pairs (n = 186). Heritability estimates for bone mineral apparent density (BMAD; g/cm3) were marginally lower but remained statistically significant at all sites (femoral neck, 51%; lumbar spine, 32%; total body, 38%). Maternal osteopenia was associated with significant reductions in bone mass at all sites in the children (femoral neck, 0.75 SD and p < 0.0001; lumbar spine, 0.61 SD and p < 0.0001; total body, 0.43 SD and p = 0.012). Mother-child bone areal bone density correlation coefficients and prediction of low bone mass in the child were greater (but this did not reach statistical significance) if the corresponding anatomical site in the mother was used for prediction with the exception of the total body. These data confirm that heritability of bone mass extends to prepubertal children and is gender- and possibly site-specific as well as under separate genetic control to growth. Furthermore, the strength of the mother-child association is such that bone density screening of mothers would make it possible to identify most prepubertal children at higher risk of osteoporosis in later life.

Changes in the regulation of calcium metabolism and bone calcium content during growth in the absence of endogenous prolactin and during hyperprolactinemia: A longitudinal study in male and female Wistar rats

Since endogenous prolactin has been shown to enhance food consumption, calcium absorption, and bone calcium turnover in the pregnant rat, the role of endogenous prolactin in the regulation of calcium metabolism was investigated in 3-day balance studies of female Wistar rats from the age of 3 to 11 weeks. The study was divided into two parts. In part I, calcium metabolism in males and females was compared. In part II, 3-week old female rats were divided into 5 groups: (i) control animals receiving 0.9% NaCl; (ii) animals receiving 6 mg bromocriptine/kg/day (- PRLendo group); (iii) animals receiving 2.5 mg ovine prolactin/kg/day (+PRLexo); (iv) sham-operated animals receiving 0.9% NaCl, and (v) animals with two extra pituitaries implanted under the renal capsule, receiving 0.9% NaCl (AP group). Results showed that rapid growth occurred between 3 and 6 weeks with maximum fractional calcium absorption and calcium retention at 5 weeks of age in both sexes. The data also showed a physiological significance of endogenous prolactin in enhancing calcium absorption and retention in 5 week old rats. In an absence of prolactin, peak calcium absorption was delayed in 7-week old animals, and vertebral calcium content of 11-week old animals was reduced by 18%. Hyperprolactinemia in the AP group was found to enhance fractional calcium absorption and calcium retention at 7, 9, and 11 weeks and increased the femoral calcium content by 16%. It could be concluded that a physiological role of prolactin is the stimulation of calcium absorption and maintainance of bone calcium content during growth and development.Key words: bone calcium content, calcium absorption, calcium balance, hyperprolactinemia, prolactin.

Adolescents: at increased risk for osteoporosis?

Perhaps the most important factor in the primary prevention of osteoporosis is the attainment of an optimal peak bone during adolescence. In addition to endogenous factors, such as genetic and ethnic background, environmental factors such as dietary habits, physical activity, and sex hormone therapy, influence the accretion of bone mass during this critical period of skeletal growth. First, calcium dietary intake in adolescents is generally well less than the current recommended RDA of 1200 mg/day. Multiple studies of children and adolescents have demonstrated increases in bone mass with dietary calcium supplementation. Second, regarding physical activity, the overall impression is that a moderate amount of particularly weight-bearing exercise has a positive impact on bone. There appears, however, to be a threshold of intensity of physical activity over which a negative impact on bone occurs, particularly when the exercise is of an anaerobic nature or occurring in very thin, amenorrheic participants. Third, previous research suggests that the various forms of hormonal contraception exert differing effects on bone mass in adolescents, with levonorgestrel implants and combined oral contraceptives may be associated with a more positive effect on bone mass compared with that observed with depot medroxyprogesterone acetate. From a clinical perspective, approaches to optimizing peak bone mass in adolescents would include increasing calcium intake, whether in the form of dairy products, fortified foods, or supplements as well as encouraging participation at a moderate level, in weight-bearing exercise. Last, in adolescents with extensive risk factors and predicted long duration of use, subdermal implants or combined oral contraceptives may be the optimal hormonal methods of birth control.

Determination of bone mineral density of the hip and spine in human pedigrees by genetic and life-style factors

In 40 human pedigrees with 563 subjects, we evaluated the contribution of genetic and life-style factors (exercise, smoking, and alcohol consumption) and the interactions between non-genetic factors in determining bone mineral density (BMD) of the hip and spine. In our analysis, we adjusted for age, weight, height, menopausal status in females, life-style factors, and the significant interactions among these factors. For the spine and hip BMD, heritabilities (h(2)) (+/- SE) were, respectively, 0.68 (0.21) and 0.86 (0.28) in males and 0.64 (0.13) and 0.67 (0.14) in females. Exercise had significant beneficial effects for male spine BMD and female hip BMD. Alcohol consumption experienced in our sample had significant beneficial effects on hip BMD in both sexes. Although the main effect of smoking was not significant, there were significant interaction effects between smoking and other important factors (e.g., exercise, weight, alcohol consumption). For example, for female spine BMD, exercise had significant beneficial effects in smokers; however, its effect in non-smokers was non-significant. This result indicates that exercise may reduce deleterious effects of smoking (if any) on BMD, but may have minor effects in increasing BMD in non-smokers. The various interaction effects among risk factors explicitly revealed here for the first time indicate that the detailed effects and direction of individual risk factors may depend on the presence and magnitude of other factors. Weight invariably affected BMD of the hip and spine in both sexes. Age effects were significant for hip BMD, but not for male spine BMD.

Role of calcium in bone health during childhood

A discussion of observational and longitudinal studies examining the effect of early-life calcium intake on bone health is provided. A critical analysis of pediatric calcium supplementation trials is conducted by determining annualized percent changes in bone mineral density (BMD). The focus of the analysis is to identify consistent findings at specific bone sites, determine whether effects differed by the age of children studied, and establish the relationship between bone changes and baseline calcium intake. We found that increases in BMD owing to higher calcium intake among children appear to occur primarily in cortical bone sites, are most apparent among populations with low baseline calcium intakes, and do not seem to persist beyond the calcium supplementation period. Older (e.g., pubertal) children appear to have greater annual increases in lumbar BMD than younger (e.g., prepubertal) children. The annual percent increase in midradius BMD appears to be greater at higher intakes among the older children, but such a relationship is less apparent among the younger children.

Effect of deconditioning on cortical and cancellous bone growth in the exercise trained young rats

Exercise enhances bone growth and increases peak bone mass. The aim of this study was to determine whether or not 4 weeks of deconditioning after 8 weeks of exercise in growing rats would result in a decrease in bone gain or reverse the benefits of exercise. Fifty 4-week-old female Sprague-Dawley rats were randomized by a stratified weight method into 5 groups with 10 rats in each group: 8 weeks exercise (8EX), 8 weeks sedentary control (8S), 12 weeks exercise (12EX), 8 weeks exercise followed by 4 weeks sedentary (8EX4S), and 12 weeks sedentary control (12S). The exercise consisted of running on a treadmill with a 5 degrees slope at 24 m/minute for 1 h/day and 5 days/week. After each period of exercise, cancellous and cortical bone histomorphometry were performed on double fluorescent labeled 5-microm-thick sections of the proximal tibia and 40-microm-thick sections of the tibial shaft, respectively. Eight and 12 weeks of exercise resulted in a significant increase in the body weight and gastrocnemius muscle weight by two-way analysis of variance (ANOVA). The femoral wet weight (mg; mean +/- SD; 8EX, 781 +/- 45.1 vs. 8S, 713 +/- 40.5; p < 0.05; 12EX, 892 +/- 41.6 vs. 12S, 807 +/- 19.8; p < 0.05) was significantly higher in the exercise group than that in the respective control groups. The femoral wet weight and bone volume (BV) of the 8EX4S group (818 +/- 46.2 mg and 531 +/- 31.2 microl, respectively) were significantly lower than those of the 12EX group (p < 0.05) and did not differ significantly from those of the 12S groups. The cancellous BV was significantly higher in the 8EX and 12EX groups than that in the respective sedentary groups (p < 0.05). The cortical bone area of the tibial shaft was also significantly higher in the 12EX than that in the 12S group (p < 0.05). The increase in the cancellous BV or cortical bone area was caused by an increase in the mineral apposition rate (MAR), without a significant effect in the labeled perimeter. The bone formation rate (BFR; microm3/microm2 per day) in the cancellous bone (12EX, 27.9 +/- 7.74 vs. 12S, 15.4 +/- 4.56; p < 0.05) or periosteal surface (12EX, 127.6 +/- 27.7 vs. 12S, 79.5 +/- 18.6; p < 0.05) was significantly higher in the exercised groups than that in the respective control group (p < 0.05). Again, deconditioning resulted in a decrease in the cancellous BFR, BV, periosteal BFR, and cortical bone area to levels not significantly different from the 12S group. In conclusion, our findings showed that exercised growing rats, when deconditioned, lost the benefits gained through exercise and their bone parameters were reduced to levels not different from the sedentary control. Thus, continued exercise is required to maintain high bone mass.

Estrogen replacement therapy in the management of osteopenia related to eating disorders

The effect of hormone replacement therapy on the bone mineral content of hypoestrogenic subjects depends on the pathogenesis of the disease as well as on the dosage and route of administration. This is particularly true in hypoestrogenism related to eating disorders. We present a longitudinal study of 26 young women with diet-induced amenorrhea compared with a group of subjects with POF. The study protocol included the quantification of weight loss, the endocrine profile (follicle-stimulating hormone, luteinizing hormone, prolactin, E2, FT3, FT4, thyroid-stimulating hormone, and cortisol), the evaluation of markers of bone turnover (GLA, OSTK-PR, ALP, OHP, and DPYR), and spinal bone density by DEXA at observation and after weight recovery. No hormone replacement therapy was administered. Mean BMD and Z scores before and after recovery do not differ significantly; OHP and DPYR appear significantly higher during basal evaluation, whereas GLA and ALP do not. Data on the impact of oral contraceptive use on bone mineral density are controversial. We particularly discuss the question of long-term treatment with 20 micrograms ethinyl estradiol pills on peak bone mass acquisition during adolescence.

The bioavailability of dietary calcium

This update focuses on the bioavailability of dietary calcium for humans. Fundamentals of calcium metabolism, intestinal absorption, urinary excretion and balance are recalled. Dietary factors, especially lactose and other milk components, influencing calcium bioavailability at intestinal and renal levels are reviewed. A critical examination of all the methods used for evaluating calcium bioavailability is made. This includes in vitro assays, classical and isotopic balances, urinary excretion, isotope labeling in the urine, plasma and bones, long term evaluation of bone mineralization and the use of biological bone markers. Importance and advantages of animal models are discussed. The state of the art in the comparative bioavailability of calcium in foods is detailed including a comparison of sources of calcium (dairy products and calcium salts) in human studies and in some animal studies, casein phosphopeptides, proteins, lactose and lactase and their relation with calcium bioavailability (in humans and rats). An update on the consumption of dairy products and bone mass is presented. Emphasis on peculiarities and advantages of calcium in milk and dairy products is given.

Calcium, dairy products and osteoporosis

Osteoporosis is a multifactorial disorder in which nutrition plays a role but does not account for the totality of the problem. 139 papers published since 1975 and describing studies of the relationship of calcium intake and bone health are briefly analyzed. Of 52 investigator-controlled calcium intervention studies, all but two showed better bone balance at high intakes, or greater bone gain during growth, or reduced bone loss in the elderly, or reduced fracture risk. This evidence firmly establishes that high calcium intakes promote bone health. Additionally, three-fourths of 86 observational studies were also positive, indicating that the causal link established in investigator-controlled trials can be found in free-living subjects as well. The principal reason for failure to find an association in observational studies is the weakness of the methods available for estimating long-term calcium intake. While most of the investigator-controlled studies used calcium supplements, six used dairy sources of calcium; all were positive. Most of the observational studies were based on dairy calcium also, since at the time the studies were done, higher calcium intakes meant higher dairy intakes. All studies evaluating the issue reported substantial augmentation of the osteoprotective effect of estrogen by high calcium intakes. Discussion is provided in regard to the multifactorial complexity of osteoporotic response to interventions and to the perturbing effect in controlled trials of the bone remodeling transient, as well as about how inferences can validly be drawn from the various study types represented in this compilation.

Bone health and osteoporosis

Good bone health is important to everyone, regardless of age. Osteoporosis is a preventable disease, and steps for increasing bone mass should begin at an early age. To increase bone mass, much of the recent evidence suggests that the best time for intervention with calcium or exercise may be during the prepubertal years. In the older female athlete, BMD is typically well above normal, but even young amenorrheic athletes can have bone density values equal to that of an elderly osteoporotic woman. Myriad treatment options are available for the person with low bone mass, but prevention is a much more preferable alternative.

Prolactinomas in adolescents: persistent bone loss after 2 years of prolactin normalization

OBJECTIVE

To evaluate the effect of hyperprolactinaemia and its treatment with dopamine-agonists on bone mass and turnover in adolescent patients compared to adults.

PATIENTS

Forty patients with hyperprolactinaemia (20 with disease onset during adolescence and 20 during adulthood) and 40 healthy control subjects.

DESIGN

Open transverse (in patients and controls) and open longitudinal (in the patients).

MEASUREMENTS

Bone mineral density (BMD) at lumbar spine and femoral neck, serum osteocalcin (OC) and urinary cross-linked N-telopeptides of type-1 collagen (Ntx) levels were evaluated in patients and controls. In the 40 patients, bone mass and turnover were re-evaluated after 12 and 24 months of treatment with bromocriptine (BRC, dose 2.5-10 mg daily), quinagolide (CV, dose 0.075-0.3 mg daily) or cabergoline (CAB, dose 0.5-1.5 mg weekly).

RESULTS

Transverse study: BMD values were significantly lower in hyperprolactinaemic patients than in controls, both at lumbar spine (0.81 +/- 0.01 vs. 1.010 +/- 0.01 g/cm2; P < 0.001) and femoral neck (0.71 +/- 0.01 vs. 0.873 +/- 0.03 g/cm2; P < 0.001). Thirty-two patients (80%) had osteoporosis and/or osteopenia at one or both skeletal sites. A significant inverse correlation was found between T score values measured at lumbar spine and femoral neck and the estimated disease duration. BMD was significantly lower in young than adult patients both at lumbar spine (T score, -2.4 +/- 0.1 vs. -1.4 +/- 0.3, P < 0.01) and at femoral neck (T score, -2.1 +/- 0.05 vs. -1.5 +/- 0.2, P < 0.05). Similarly, serum OC levels were significantly lower (2.0 +/- 0.11 vs. 9.1 +/- 2.4 micrograms/l, P < 0. 01) while Ntx levels were significantly higher in patients than in controls (129.2 +/- 1.7 vs. 80.7 +/- 2.9 nmol Bone collagen equivalent (BCE)/mmol creatinine; P < 0.001). A significant inverse correlation was found between prolactin (PRL) levels and OC levels, lumbar and femoral T score values, as well as between disease duration and OC levels, lumbar and femoral T score values. A significant direct correlation was also found between Ntx levels and PRL levels and disease duration. Longitudinal study: Normalization of serum PRL levels was obtained in all patients after 6-12 months of treatment. A significant increase of serum OC levels together with a significant decrease of Ntx levels was observed after 12 and 24 months of treatment (P < 0.01). Urinary and serum calcium, phosphorus, creatinine, and serum alkaline phosphatase and parathyroid hormone levels did not change during the study period in all patients. After 12 months of therapy OC and Ntx concentrations were restored to normal. A slight but not significant increase of BMD values was recorded after 12 and 24 months of treatment. After 12 months of treatment the percent increment of BMD values in the whole group of patients was 1.13 +/- 0.6% at lumbar spine and 1.2 +/- 0.4% at femoral neck level, whereas after 24 months, it was 2.8 +/- 0.7% at lumbar spine and 3.5 +/- 0.7% at femoral neck level. After 12 months of treatment, the percent increment of BMD values was 0.7 +/- 0.2% and 1.6 +/- 1.1% at lumbar spine and 0.9 +/- 0.5% and 1.6 +/- 0.5% at femoral neck level in the young and adult patients, respectively, whereas after 24 months, it was 2.1 +/- 0.8% and 3.4 +/- 1.3% at lumbar spine and 2.6 +/- 0.8% and 4.4 +/- 1.0% at femoral neck level in the young and adult patients, respectively.

CONCLUSIONS

Adolescents with prolactinoma have osteopenia or osteoporosis, a finding that strengthens the need for a prompt diagnosis. Since normalization of PRL concentrations by dopamine agonist therapy is unable to restore the bone mass, other therapeutic approaches should be considered in order to prevent further long-term problems.

Women and the orthopaedic surgeon. Changing the relationship

Women are disproportionately disabled by musculoskeletal conditions. For biologic and lifestyle reasons, musculoskeletal health is one of the areas of medicine in which the differences between men and women are most marked. Thus, an approach tailored to women, not just an approach based on what has worked for men, often is needed. How orthopaedists treat women will become an even more pressing issue in the years ahead. Demographic trends predict that the majority of senior citizens will be women in whom chronic conditions frequently involve a musculoskeletal problem. Even at earlier ages, women will present more frequently with musculoskeletal conditions because they participate in a broader range of sports and careers. The current study presents a lengthy list of action items that the orthopaedic surgeon should consider as he or she approaches the treatment of women. Many of these items involve anticipating musculoskeletal problems, and convincing patients to take appropriate preventive steps. Because so many patients are treated by physicians who are not orthopaedists for their musculoskeletal problems, a successful preventive approach presents orthopaedists with the opportunity to win the confidence and respect of a new generation of patients.

A noninvasive measure of physical maturity as a predictor of bone mass in children

OBJECTIVE

The purpose of this study was to describe the accumulation of whole body bone mass in a longitudinal study of prepubertal boys and girls using Roche's physical maturity index as a measure of developmental age.

METHODS

We measured 561 children (39% white, 61% African-American) from a suburban school district, representing an ethnically mixed, middle-class community adjacent to Detroit. Anthropometric measures taken for the present study included recumbent length (cm), stature (cm), weight (kg), whole body bone mineral content (WBBMC in g) and a noninvasive measure of physical maturity (PM%). PM% was calculated from published formulae derived from data from the Fels Longitudinal Study, using recumbent length, weight, midparental stature, age, and age- and gender-specific regression coefficients.

RESULTS

At average age 9.9 (+/-0.6) years, there were no significant gender differences in stature, recumbent length, weight, or WBBMC in either ethnic group. Average PM for girls was significantly greater than that for boys within each ethnic group. There were no significant ethnic differences in PM in either gender. Stature and WBBMC were significantly different in the two ethnic groups for both boys and girls. Regressions of WBBMC on PM and chronological age indicated that PM explained more of the variance in WBBMC than did age (r2 ranging from 0.28 to 0.75 for PM versus 0.01 to 0.06 for age). In the case of African-American boys, r2 was similar (0.09 for PM and 0.06 for age).

CONCLUSIONS

PM is a useful, noninvasive measure of developmental age that is significantly correlated with bone mass in children. Our study also indicates that PM is a better predictor of WBBMC than chronological age. Because PM can be calculated without using invasive and potentially expensive methods, PM may be useful in some clinical as well as research settings.

A prospective study of quantitative ultrasound in children and adolescents

The accrual of optimal bone mass during childhood and adolescence is essential for the formation of a skeleton that will meet structural needs throughout life. Assessing bone health of children is becoming increasingly important in order to identify those who require interventions, and quantitative ultrasound (QUS) has appeal for these assessments. The purpose of this prospective study was to characterize changes in QUS values in 328 healthy children and adolescents over a 3-yr period. Measurements of QUS, height, weight, nutrient intake, fracture history, and Tanner stage were made at baseline and 3 yr later. Both females and males experienced significant increases in QUS values during the study. The rate of change of QUS peaked at an earlier age in females than in males, and maximum accumulation rates in both genders occurred at ages at which highest accumulation rates are seen with densitometry. Females exhibited higher QUS values than males during puberty, also similar to results for dual X-ray absorptiometry (DXA). This is the first report of prospective data of QUS in children and adolescents. Our findings that QUS values change during childhood and adolescence in a manner similar to DXA values, the "gold standard," provide support for the validity of using QUS to assess bone health in children and adolescents.

Using stable isotopes to assess mineral absorption and utilization by children

Adequate mineral intake is a crucial part of a healthy diet for children-it supports appropriate growth and development and provides protection against childhood conditions like anemia and helps to prevent future adult diseases such as osteoporosis. Challenges in performing and interpreting studies in infants and children have hampered the accurate assessment of their mineral utilization. Many of the most powerful techniques used in adults, such as radioisotope testing, are not appropriate for use in children. In recent years, advanced mineral stable-isotope techniques have been developed to fill this gap. Pediatric applications include studies of calcium absorption and kinetics during puberty and evaluation of the calcium-iron interaction in infants and toddlers. The effects of genetics in determining calcium absorption and bone turnover may become an important research area. The goals and methods of ongoing mineral stable-isotope research in infants and children are examined in this report. In the past, the cost and difficulties in obtaining isotopes have limited such research. This situation has improved considerably, although relatively few nutrition research laboratories are prepared to perform sample analyses.

Bone mineral density testing and osteoporosis education improve lifestyle behaviors in premenopausal women: a prospective study

One way to decrease the risk of osteoporosis is to maximize peak bone mass. Peak bone mass may be moderately influenced by lifestyle behaviors: increasing calcium and exercise, decreasing alcohol intake and smoking may increase peak bone mass. We examined the effects of osteoporosis education and bone mineral density (BMD) testing on self-reported lifestyle behaviors in 669 premenopausal women enrolled in a prospective study to assess determinants of peak bone mass. Study participants completed a questionnaire that assessed lifestyle behaviors, received pamphlets about osteoporosis, and had BMD testing. One year later, the women completed a similar questionnaire. After education about osteoporosis and BMD testing, women reported that they were less likely to smoke (odds ratio [OR] = 0.55; 95% confidence interval [95% CI]: 0.28-1.0), consume alcohol (OR = 0.13; 95% CI: 0.04-0.34), and caffeinated beverages (OR = 0. 43; 95% CI: 0.27-0.68). Women were more likely to use calcium supplements (OR = 4.3; 95% CI: 3.04-6.2), vitamin D supplements (OR = 12.6; 95% CI: 7.4-22.9), and drink at least one glass of milk a day (OR = 13.3; 95% CI: 7.8-23.9). Further, women with low bone mass were more likely to use calcium supplements (OR = 1.7; 95% CI: 1.2-2.3) and vitamin D supplements (OR = 1.6; 95% CI:1.1-2.2) compared with women who had normal bone mass. Thus, our intervention improved self-reported lifestyle behaviors in premenopausal women. Such behaviors may ultimately increase peak bone mass and decrease the risk of developing osteoporosis.

Previous milk consumption is associated with greater bone density in young women

BACKGROUND

Dietary calcium and milk intakes at specific ages may influence bone mineral measures at specific sites during development of peak bone mass.

OBJECTIVE

Relations of previous milk intake and current calcium intake to current bone mineral measures were investigated in young women.

DESIGN

A food-frequency interview and recall of previous milk intake from early childhood to 12 y of age and during adolescence (13-19 y) were completed in a cross-sectional analysis in young women (age 18-31 y; n = 224). Three levels of previous milk intake were defined: 1) infrequently or never, 2) sometimes, and 3) at every or almost every meal. Total body (TB), femoral neck, radius (R), and spine (S) bone mineral density (BMD) and bone mineral content (BMC) were determined by using dual-energy X-ray absorptiometry.

RESULTS

Childhood and adolescent milk intakes were positively correlated (r = 0.66). Childhood and adolescent milk intakes correlated with current calcium intakes (r = 0.26 and 0.33, respectively). Adolescent milk intake correlated with RBMD (r = 0.16). When weight was controlled for, adolescent milk intake correlated with TBBMD (r = 0.16), TBBMC (r = 0.21), SBMC (r = 0.16), RBMD (r = 0.18), and RBMC (r = 0.15). Current calcium intakes correlated with SBMC (r = 0.17). Regression analyses supported these results.

CONCLUSIONS

Results were consistent with the hypothesis that higher milk intake during adolescence is associated with greater total body, spine, and radial bone mineral measures during development of peak bone mass, whereas current calcium intakes may influence SBMC. In addition, milk intake at a younger age may contribute to similar habits of milk intake later in life.

Differential effect of treadmill exercise on three cancellous bone sites in the young growing rat

The aim of the present study was to examine cancellous bone changes induced by exercise on three different skeletal sites, the lumbar vertebra, the proximal, and the distal tibia, in the young growing rat. Forty 4-week-old female Sprague-Dawley rats were randomized into 4 groups of 10 animals each; 8 weeks exercise (8EX), 8 weeks sedentary control (8CON), 12 weeks exercise (12EX), and 12 weeks sedentary control (12CON). The exercise regimen consisted of treadmill running at 24 m/min 1 hr per day 5 days a week. After each period of exercise, the proximal and distal tibial metaphyses (PTM and DTM, respectively) and the fifth lumbar (L5) vertebral body were processed for histomorphometry of the cancellous bone (secondary spongiosa) and cortical periosteum. Eight and twelve weeks of exercise significantly increased the mineral apposition rate and bone formation rate in the PTM and DTM, and 12 weeks of exercise significantly increased the labeled perimeter in the DTM, compared with the age-matched controls. Eight and twelve weeks of exercise significantly increased cancellous bone volume in the PTM (mean +/- standard deviation, 8EX; 19.1 +/- 2.9% vs 8CON; 14.3 +/- 3.1%, P < 0.05 and 12EX; 18.8 +/- 3.5% vs 12CON; 15.2 +/- 3.3%, P < 0.05), and 12 weeks exercise significantly increased cancellous bone volume in the DTM, compared with age-matched control (12EX; 32.5 +/- 7.7%, 12CON; 22.2 +/- 4.8%, P < 0.05). The increase in cancellous bone volume by 12 weeks exercise was higher in the DTM than that in the PTM (43.4% and 24.0%, respectively). On the other hand, the exercise did not significantly affect cancellous bone volume and bone formation in the L5 vertebral body, although the cortical periosteal bone formation rate and the L5 vertebral bone mass were increased. These findings suggest that cancellous bone adaptation to treadmill exercise is site specific, and the effect may be influenced by factors such as mechanical loading and metaphyseal bone architecture in the young growing rat.

Familial resemblance of bone mineral density (BMD) and calcaneal ultrasound attenuation: the BMD in mothers and daughters study

The familial resemblance in bone mineral density (BMD) and calcaneal broadband ultrasound attenuation (BUA) was examined in 207 mother-daughter pairs. Mothers were participants in the Study of Osteoporotic Fractures. Three groups of daughters were recruited based on their maternal history of "fracture," "low BMD" without fracture (< 0.58 g/cm2, t-score < -2.5), and "normal BMD" without fracture (> 0.67 g/cm2, t-score > -1.6). Data on other potentially heritable factors known to influence BMD and BUA were also collected. BMD was measured at the hip, spine, whole body, and calcaneus. Calcaneal BUA was assessed using the Walker-Sonix UBA 575. Total hip and femoral neck BMD were significantly lower (5.0-8.0%, p < 0.017) among daughters, in particular premenopausal daughters, of mothers with established osteoporosis ("fracture" or "low BMD") compared with daughters of mothers at lower risk of osteoporosis ("normal BMD"). BUA did not differ across daughter groups. Lifestyle characteristics (dietary calcium, smoking, physical activity) were not highly correlated in mothers and daughters. Height, weight, and body composition were significantly correlated within mother-daughter pairs and could be a potential mechanism by which BMD is inherited. Among pre- and postmenopausal daughters, heritability estimates ranged from 50-63% and 34-48%, respectively. Heritability for calcaneal BUA (53%) was evident among postmenopausal daughters only. In conclusion, familial association in BMD was strongest among premenopausal daughters. Estimates of heritability suggest that maternal BMD and BUA are important independent predictors of BMD and BUA among daughters, reinforcing the importance of prevention and early intervention among women with a positive family history of osteoporosis.

Nutrient intake and food group consumption of 10-year-olds by sugar intake level: the Bogalusa Heart Study

OBJECTIVE

The effect of total sugar intake on nutrient intake and food group consumption was examined in children.

METHODS

Twenty-four hour dietary recalls were collected on a sample of 568 ten-year-olds from two cross-sectional surveys. The population was stratified according to total sugar intake quartiles: < or = 25th (46 g/1000 kcal), 25-50th (67 g/1000 kcal), 50-75th (81 g/1000 kcal) and > or = 75th (106 g/1000 kcal).

RESULTS

No significant difference was shown in energy intakes across the quartiles and no significant race or gender differences were observed in mean total sugar intakes. However, with increasing total sugar intake, there was a significant linear decrease in mean intakes of protein, fat, saturated fat, starch, cholesterol, sodium, vitamins B6 and E, thiamin, niacin, iron, and zinc; and a significant linear increase in mean intakes of carbohydrate, fructose, lactose, sucrose, vitamin D, and calcium. Eating patterns reflected the differing nutrient intakes, with high sugar consumers having significantly higher intakes of total g of candy, beverages and milk and lower intakes of total g of meats, and cheese than lower sugar consumers. The nutritional quality of children's diets high in total sugar appear to be adequate regarding vitamin and mineral intakes and are closer to meeting current dietary fat recommendations.

Lessons learned about adolescent nutrition from the Minnesota Adolescent Health Survey

In 1986-1987, more than 30,000 adolescents completed the Minnesota Adolescent Health Survey, a comprehensive assessment of adolescent health status, health behaviors, and psychosocial factors. Although the survey included relatively few items on nutrition-related issues, a wealth of knowledge about adolescent nutrition was gained. Lessons learned from a decade of subsequent analyses of data collected in the survey and implications for working with youth are summarized in this article. Major concerns identified included high prevalence rates of inadequate intake of fruits, vegetables, and dairy products; unhealthful weight-control practices; and overweight status. For example, inadequate fruit intake was reported by 28% of the adolescents and inadequate vegetable intake was reported by 36%. Among female adolescents, 12% reported chronic dieting, 30% reported binge eating, 12% reported self-induced vomiting, and 2% reported using diuretics or laxatives. Some of the risk factors for inadequate food intake patterns or unhealthful weight-control practices included low socioeconomic status, minority status, chronic illness, poor school achievement, low family connectedness, weight dissatisfaction, overweight, homosexual orientation among male adolescents, and use of health-compromising behaviors. To improve adolescent eating behaviors, the results suggest a need for innovative outreach strategies that include educational and environmental approaches. Dietitians play a key role in developing interventions and promoting research in the field of adolescent nutrition.

Osteoporotic fracture among older U.S. women: risk factors quantified

The purpose of this study was to develop a predictive model for osteoporotic fracture among a national sample of 2,325 women ages 50 years and older. Predictors for examination included age, race, heredity, body mass index (BMI), physical activity, smoking status, alcohol use, and dairy product use. Analyses were conducted using Standard Analysis System (SAS) procedures. Strong risk factors predicting osteoporotic fracture included age, race, low BMI, and inactivity. Recommendations emphasize screening of high-risk women, achieving and maintaining health body weights for underweight women, and obtaining moderate physical activity. Promotion of healthy body weights for women of all ages is emphasized. Recommendations also include encouraging widespread physician, patient, and public education regarding osteoporotic fracture.

Effect of central precocious puberty and gonadotropin-releasing hormone analogue treatment on peak bone mass and final height in females

To evaluate the effect of central precocious puberty (CPP) and its treatment with gonadotropin-releasing hormone (GnRH) analogues on final height and peak bone mass (PBM), we measured lumbar bone mineral density (BMD) in 23 girls at final height. Patients were distributed in two groups. Group 1: 14 patients with progressive CPP were treated with GnRH analogues; seven patients received buserelin (1600 microg/daily), subsequently switched to depot triptorelin (60 microg/kg/26-28 days); seven patients were treated with depot triptorelin (60 microg/kg/26-28 days); mean age of treatment was 6.2 years (range 2.7-7.8 years); the treatment was discontinued at the mean age of 10.1 years (range 8.7-11.3 years); final height was reached at the mean age 13.4 years (range 12.0-14.9 years). Group 2: 9 patients (mean age 6.5 years, range 4.8-7.7 years) with a slowly progressing variant of CPP were followed without treatment; final height was reached at the mean age 13.6 years (range 12.5-14.8 years). Lumbar BMD (L2-L4 by dual energy X-ray absorptiometry) was measured in all patients at final height. In group 1, final height (158.9+/-5.4 cm) was significantly greater than the pre-treatment predicted height (153.5+/-7.2 cm, P < 0.001), but significantly lower than mid-parental height (163.2+/-6.2 cm, P < 0.005). Subdividing the girls of group 1 according to the bone age at discontinuation of therapy (i.e. < or =11.5 years, n=5, or > or =12.0 years, n=9), the former patients had a final height significantly higher than the latter (163.7+/-3.9 cm vs 156.5+/-4.6 cm, P < 0.02). In group 2, final height (161.8+/-4.6 cm) was similar to the pre-treatment predicted height (163.1+/-6.2 cm, P=NS) and was not significantly different from mid-parental height (161.0+/-5.9 cm). BMD values (group 1: 1.11+/-0.14 g/cm2, group 2: 1.22+/-0.08 g/cm2) were not significantly different from those of a control group (1.18+/-0.10 g/cm; n=20, age 16.3-20.5 years) and the patients' mothers (group 1: 1.16+/-0.07 g/cm2, n=11, age 32.9-45.1 years; group 2: 1.20+/-0.08 g/cm2, n=7, age 33.5-46.5 years). In group 1, the girls who stopped therapy at a bone age < or =11.5 years had significantly higher BMD (1.22+/-0.10 g/cm2) compared to those who discontinued therapy at a bone age > or =12.0 years (1.04+/-0.12 g/ cm2, P < 0.05).

CONCLUSION

In girls with progressive CPP, long-term treatment with GnRH analogues improves final height. A subset of patients with CPP does not require treatment because good statural outcome (slowly progressing variant). In CPP, the abnormal onset of puberty and the long-term GnRH analogue treatment do not impair the achievement of PBM. In GnRH treated patients, the discontinuation of therapy at an appropriate bone age for pubertal onset may improve both final height and PBM.

Morphometric skeletal traits, femoral measurements, and bone mineral deposition in mice with agonistic selection for body conformation

Morphometric skeletal traits, femoral histomorphometry, and bone mineral deposition were investigated in two lines of mice (CBi+ and CBi-) divergently selected for body conformation (CBi+: high body weight, long tail; CBi-: low body weight, short tail) and in the unselected control line CBi. Linear morphometric measurements, absolute and relative skeletal weights, absolute and relative femoral weights, and total biomass sustained per unit of total or tail-less skeletal weight were increased in CBi+ mice in comparison with controls. This greater biomass implies a greater mechanical demand that is satisfied by a heavier skeleton. Looking specifically to the femur, CBi+ mice had heavier bones, both absolute and relative, with a greater diameter and a greater cortical thickness, resulting in a greater cortex/diameter ratio than controls. Although morphometric measurement and absolute skeletal weight were lower in CBi- than in CBi mice, the relative skeleton weight and the biomass sustained per unit of skeletal weight were not modified in the downward selection line when compared with controls. Therefore, CBi- mice did not exhibit a greater mechanical demand as CBi+ mice did. These results led us to consider at least three main aspects: bone length growth; cortical thickness/bone diameter ratio; and bone calcification. The long bones appeared to have a genetically determined predisposition to achieve a given length, which, however, could be modified by artificial selection. Cortical thickness would be directly related to the biomass sustained. This variable increased in CBi+ mice, a genotype that supports a greater biomass than controls, and did not change in CBi- mice, which sustained the same biomass as CBi. The pattern of mineral deposition did not accompany the functional demand because it was higher in CBi- than in CBi+; however, as artificial selection separately affected bone material quality and bone architectural design, these genotypes could express architectural modifications that override any change in bone material quality.

Is there a relationship between physical activity and dietary calcium intake? A survey in 10,373 young French subjects

PURPOSE

The purpose of this study was to discuss, in the light of the results of a survey, the calcium ration of a sample of French youth and to determine whether various sports activities can be related to dietary calcium intake.

METHODS

Physical activity was evaluated using Baecke's questionnaire. Calcium intake was evaluated using a food frequency oriented questionnaire. The survey was performed on a population of 10,373 subjects (6,966 males and 3,407 females) including three different groups of subjects: school children and college students, military personnel, and athletes registered in sports federations. The mean age of this population was 19 +/- 9 yr, ages ranging between 7 and 50 yr.

RESULTS

The mean amount of declared calcium intake (DCI) for the total population was 1242 +/- 843 mg per 24 hr (mg x d(-1)). Fifty percent of this population consumed less than 1000 mg x d(-1) and 13% less than 500 mg x d(-1). There was no significant relationship between the index of activity and declared calcium intake. Calcium intake decreased with age and was lower in females compared to males.

CONCLUSIONS

The subjects trained in individual endurance sports such as triathlon, biking, and road running have a lower DCI than subjects trained in team sports such as volley ball, handball, or basketball. This survey, performed on a large population, does indicate that for half of them daily calcium intake is below the threshold of 1,000 mg x d(-1) considered the daily requirement covering the needs of a population without age or gender distinction and that calcium intake is not related to the level of physical activity.

Bone mineral density in prepubertal children with beta-thalassemia: correlation with growth and hormonal data

Patients with beta-thalassemia major (beta-thalassemia) frequently have bone disorders of multifactorial etiology. We attempted to analyze the relationship between the bone mineral density ([BMD] measured by dual-photon absorptiometry) and auxanologic parameters, degree of siderosis, function of the growth hormone (GH)/insulin-like growth factor-I (IGF-I)/IGF-binding protein-3 (IGFBP3) axis, calcium-phosphate balance, parathyroid hormone (PTH), and cytokines (interleukin-1beta [IL-1] and tumor necrosis factor-alpha [TNF-alpha]) in 30 prepubertal children with beta-thalassemia major and 15 age-matched children with constitutional short stature (CSS), who have normal glucose tolerance and thyroid function. Children with beta-thalassemia had a significantly decreased BMD and mean BMD% for age and sex (0.75+/-0.24 g/cm2 and 71%+/-10%, respectively) versus children with CSS (1.06+/-0.3 g/cm2 and 92%+/-7%, respectively). Thalassemic patients had significantly lower circulating concentrations of IGF-I and IGFBP3 (49+/-21 ng/mL and 1.2+/-0.25 mg/L, respectively) compared with control children (153+/-42 ng/mL and 2.1+/-0.37 mg/L, respectively). The GH response to provocation by clonidine and glucagon was defective (peak GH < 7 microg/L) in 12 of the 30 thalassemic children. Serum concentrations of IL-1beta and TNF-alpha did not differ among the two study groups. Hypocalcemia was detected in five of the 30 thalassemic patients: hypoparathyroidism was diagnosed in two of the five and rickets in the other three. BMD was highly correlated with the circulating concentrations of IGF-I and IGFBP3, as well as with the auxanologic parameters (age, weight, height, height standard deviation score [HSDS], and body mass index [BMI]). It is suggested that increasing the circulating IGF-I concentration through aggressive nutritional therapy and/or GH/IGF-I therapy with supplementation with vitamin D and/or calcium might improve bone growth and mineralization and prevent the development of osteoporosis and consequent fractures in these patients. Such therapy requires blinded controlled trials.

Relation of nutrition, body composition and physical activity to skeletal development: a cross-sectional study in preadolescent females

OBJECTIVE

To examine the relation of anthropometric and growth parameters (weight, stature, body composition, age, and skeletal age), nutritional factors, and physical activity to the total body and radius bone mineral density and content and radiogrammetry parameters of the second metacarpal.

STUDY DESIGN

The study was a cross-sectional evaluation of 456 healthy, Caucasian girls, ages 8 to 13 years. Multiple regression models were created based on Cp statistics to determine the association between bone parameters and various independent variables.

RESULTS

Mean calcium intake was 956+/-381 mg/day, about 20% below the RDA of 1200 mg/day and about 36% below the threshold intake of approximately 1500 mg/day. The most significant predictors for total body and radius bone mineral density were corresponding bone areas, lean body mass, body fat, skeletal age, dietary calcium, and stature (only for total body) with corresponding R2(adjusted) of 48% and 36%. The total body and radius bone mineral content was positively associated with corresponding bone areas, lean body mass, body fat, calcium intake, and skeletal age with corresponding R2(adjusted) of 86% and 72%. Energy expenditure (corrected for BMI) was stratified into quartiles and bone mass parameters were distributed accordingly. A statistically significant difference in total body and radius bone mineral density and content was noted between the fourth and lower quartiles (ANOVA, p<0.05 to p<0.0001).

CONCLUSION

The most significant predictors of bone mass in preadolescent females evaluated in this study are bone area, lean body mass, body fat, skeletal age and dietary calcium.

Dietary restriction of energy and calcium alters bone turnover and density in younger and older female rats

To determine the influence of weight loss with or without adequate calcium intake on bone turnover and density, we examined the influence of dietary restriction of calcium or energy on body weight (BW), bone mineral density (BMD) and bone turnover in both younger (3 mo) and older (10 mo) female rats (n = 66). Diets were designed to allow feeding at two levels of calcium intake (normal = 78 mg/d and low = 15 mg/d) and two levels of energy intake (normal and 40% restriction) while keeping the intake of protein, fat, fiber, vitamins and other minerals equal between groups. Thus rats received either a control diet (CNTL), a diet restricted in calcium, energy or both for 9 wk. Energy restriction reduced BW 5-21% (P < 0.01) and elevated bone formation 10-20% (P < 0.05) in both age groups. Bone resorption was 20-40% above CNTL values (P < 0.05), in rats fed all three restricted diets. In younger rats, BMD increased over time in all groups (P < 0.05), but final BMD was lower in calcium restricted groups compared with CNTL (P < 0.01). In older rats, CNTL had a significantly greater final BMD (P < 0.05) than diet-restricted groups. These data indicate that, in both younger and older rats, dietary restriction of calcium or energy results in an elevated rate of bone turnover. BMD is compromised by calcium restriction in both younger and older rats, whereas only older rats were negatively influenced by dietary energy restriction. Thus the present study indicates a detrimental effect of low-energy diets, as well as inadequate calcium intake, on bone density in mature rats.

Do dietary calcium and age explain the controversy surrounding the relationship between bone mineral density and vitamin D receptor gene polymorphisms?

Whether vitamin D receptor (VDR) gene polymorphisms are associated with osteoporosis is highly controversial. The relationship between VDR gene polymorphisms and bone mineral density (BMD) might, however, be modified by age-related and/or environmental factors. We studied the potential association between BMD and VDR genotypes in females from prepuberty to premenopause and prospectively investigated the interaction of VDR genotypes with dietary calcium and BMD changes during childhood. Bsm I VDR gene polymorphisms and BMD at the lumbar spine (LS) and femur (neck [FN] and midshaft [FS]) were assessed in 369 healthy Caucasian females, aged 7-56 years (143 prepubertal girls, 54 peri- and postpubertal adolescents, and 172 premenopausal adults). Femoral trochanter (FT) and distal radius BMD (metaphysis and diaphysis) were also measured in 101 of the prepubertal girls who participated in a 1-year, double-blind, randomized study of calcium supplementation (850 mg/day) versus placebo on bone mineral mass accrual. Among all females, 150 (40.7%) had bb, 167 (45.3%) Bb, and 52 (14%) BB VDR genotypes. In prepubertal and adolescent girls altogether, LS BMD (Z scores) was associated with VDR genotypes and was significantly lower in BB than in Bb or bb subjects. Trends for a similar difference were also detected at the FN level as well as on the mean BMD (Z scores) of the three sites measured (LS, FN, and FS). By contrast, no BMD differences were detectable among VDR genotypes in the adults. In 101 prospectively studied prepubertal girls, calcium supplementation significantly increased BMD at most skeletal sites, except LS. After segregation for VDR genotypes (40 bb, 47 Bb, and 14 BB), a significant calcium effect was present in Bb but not bb girls, whereas in BB girls there was a positive but nonsignificant trend for a calcium effect. Moreover, dietary calcium intake was significantly correlated with BMD changes at various independent bone sites in Bb girls but not in bb girls. In contrast, BMD gain in bb girls appeared to be higher than among the other genotypes when the dietary calcium intake was low, i.e., in the absence of calcium supplements. BMD was significantly associated with VDR gene polymorphisms only before puberty, BB girls having significantly lower BMD (Z scores) than the other genotypes. By increasing dietary calcium intake, BMD accrual was increased in Bb and possibly BB prepubertal girls, whereas bb subjects had the highest spontaneous BMD accrual and remained unaffected by calcium supplements. Taking into account complex interactions between VDR gene polymorphisms and environmental factors, including calcium intake, may thus help to understand the discordant relationships between BMD and VDR gene polymorphisms.

Bone turnover response to changes in calcium intake is altered in girls and adult women in families with histories of osteoporosis

Heredity and environmental factors contribute to the development of osteoporosis. Because calcium is the major mineral in bone and adolescence is a key period in bone acquisition, we hypothesized that bone turnover would be less responsive to alterations in dietary calcium intake in both girls and adult women from families with histories of osteoporosis. To address this issue, we studied calcium kinetics in the maternal grandmother (age range 56-81 years), mother (age range 32-47 years), and granddaughter (age range 8-15 years) in 10 multigenerational families. In five families, the mother and/or grandmother had osteoporosis (bone mineral density > or = 2 SD below the age-specific mean). To examine both active and passive calcium absorption, families consumed low- (279 +/- 64 mg/day) and high- (1580 +/- 385) calcium diets for 10 days prior to administration of oral (46Ca) and intravenous (42Ca) stable isotopes. Using repeated measures analysis of variance, fractional calcium absorption, true calcium absorption, bone calcium deposition, and the balance in bone calcium turnover were all significantly affected by diet (p < 0.01). Females from nonosteoporotic families had decreased bone calcium resorption with little change in bone calcium deposition during the high-calcium study. In contrast, girls and adult women from osteoporotic families had increased both bone calcium deposition and resorption during the high-calcium period, leading to a less positive balance in bone calcium turnover. A significant interaction between bone status and diet was found for bone calcium resorption (p < 0.05) and approached significance for bone calcium deposition (p < 0.07), effects which were independent of generation. We conclude that girls and women from osteoporotic families have a significantly altered bone turnover response to acute changes in calcium intake.

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 background, 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 osteoporosis. 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 appropriate management strategies.

Abnormalities in skeletal growth in children with juvenile rheumatoid arthritis

A review of the acquisition of peak skeletal mass in normal children and studies that have been reported for children with JRA lead to the following tentative conclusions: (1) The appendicular skeleton is predominantly the overall status of skeletal mineralization; (2) a failure to develop adequate bone mineralization is virtually universal in children with JRA and is characterized by a failure of bone formation. A failure to undergo the normal increase in bone mass during puberty is common in children with JRA and markedly decreases their potential to achieve an adequate peak skeletal mass; (3) the onset of accelerated skeletal maturation with puberty is a critical period of potential intervention in JRA. Conversely, therapeutic interventions later during adolescence offer less promise of reversal of inadequate bone mineralization; and (4) the most important therapeutic maneuver is likely to be control of the inflammation process, although there is hope, at present unsubstantiated, that supplemental dietary calcium and vitamin D, and normalization of physical activity, many lead to some "catch-up" mineralization.

Can we prevent fractures?

The primary aim of any intervention in osteoporosis is the prevention of fractures in individuals who have not yet fractured or the prevention of the progression of the disease in individuals with fragility fractures. There is currently insufficient evidence to recommend either a population-based prevention strategy or a strategy based on general screening with treatment of those individuals identified at high risk. Identification of subjects with strong clinical risk factors for osteoporotic fractures with subsequent measurement or not of bone mineral density as well as those with fragility fractures constitute at present the most rational approach to fracture prevention. Current measures to prevent osteoporotic fractures aim mainly at influencing bone mass and bone turnover and reducing the risk and impact of falls. Interventions that can reduce effectively the frequency of osteoporotic fractures in subjects at risk are available and new or alternative interventions are being developed. Issues related to the impact of these interventions on public health and health economics need to be addressed and methods to calculate the clinical outcomes in a way allowing comparison with outcomes of interventions in other common diseases should be developed.

Calcium and osteoporosis

Calcium is an essential nutrient that is involved in most metabolic processes and the phosphate salts of which provide mechanical rigidity to the bones and teeth, where 99% of the body's calcium resides. The calcium in the skeleton has the additional role of acting as a reserve supply of calcium to meet the body's metabolic needs in states of calcium deficiency. Calcium deficiency is easily induced because of the obligatory losses of calcium via the bowel, kidneys, and skin. In growing animals, it may impair growth, delay consolidation of the skeleton, and in certain circumstances give rise to rickets but the latter is more often due to deficiency of vitamin D. In adult animals, calcium deficiency causes mobilization of bone and leads sooner or later to osteoporosis, i.e., a reduction in the "amount of bone in the bone" or apparent bone density. The effects of calcium deficiency and oophorectomy (ovariectomy) are additive. In humans, osteoporosis is a common feature of aging. Loss of bone starts in women at the time of the menopause and in men at about age 55 and leads to an increase in fracture rates in both sexes. Individual fracture risk is inversely related to bone density, which in turn is determined by the density achieved at maturity (peak bone density) and the subsequent rate of bone loss. At issue is whether either or both of these variables is related to calcium intake. The calcium requirement of adults may be defined as the mean calcium intake needed to preserve calcium balance, i.e., to meet the significant obligatory losses of calcium through the gastrointestinal tract, kidneys, and skin. The calcium allowance is the higher intake recommended for a population to allow for individual variation in the requirement. The mean requirement defined in this way, calculated from balance studies, is about 20 mmol (800 mg) a day on Western diets, implying an allowance of 25 mmol (1000 mg) or more. Corresponding requirements and allowances have been calculated for pregnancy and lactation and for children and adolescents, taking into account the additional needs of the fetus, of milk production, and of growth. There is a rise in obligatory calcium excretion at menopause, which increases the theoretical calcium requirement in postmenopausal women to about 25 mmol (1000 mg) and implies an allowance of perhaps 30 mmol (1200 mg) or even more if calcium absorption declines at the same time. At issue here, however, is whether menopausal changes in calcium metabolism are the cause or the result of postmenopausal bone loss. The first interpretation relies on evidence of a positive action of estrogen on the gastrointestinal absorption and renal tubular reabsorption of calcium; the latter interpretation relies on evidence of a direct inhibitory effect of estrogen on bone resorption. The calcium model for postmenopausal bone loss tends to be supported by the effect of calcium therapy. An analysis of the 20 major calcium trials in postmenopausal women reported in the last 20 years yielded a mean rate of bone loss of 1.00% per annum (p.a.) in the controls and 0.014% p.a. (NS) in the treated subjects (P < 0.001). However, trials in which calcium and estrogen have been directly compared have shown that the latter is generally more effective than calcium in that it produces a small, but often significant bone gain. This superiority of estrogen over calcium could be due to the former's dual action on calcium absorption and excretion or to a direct action of estrogen on bone itself. In older women, the importance of calcium intake is overshadowed by the strong association between vitamin D insufficiency and hip fracture. Whether this insufficiency arises primarily from lack of exposure to sunlight or to a progressive failure to activate the vitamin D precursor in the skin or both is uncertain but it is compounded by a general decline in dietary vitamin D intake with age. The biological effect is probably an impairment of calcium absorption and c

The role of dairy products and non alcoholic beverages in bone fractures among schoolage children

In order to assess consumption of the calcium rich dairy products, intake of non alcoholic beverages and physical activity as risk factors for bone fractures among schoolage children, a case control study was undertaken in Athens, Greece. During 1995 one hundred children 7 to 14 years old (74 boys and 26 girls) with single uncomplicated fractures of the upper and lower extremities and no evidence of coexisting metabolic condition affecting bone fragility were compared with 100 age- and gender-matched controls. The analysis was undertaken by modeling the data through conditional logistic regression. Several indicators point to an increased risk of fractures among physically active children, although none of the individual variables was statistically significant. Somatometric factors were not related to fractures, although children with more advanced stage of development at Tanner's scale were apparently at increased risk. Intake of dairy products and of carbonated non cola beverages was not related to the occurrence of fractures. By contrast, intake of non carbonated beverages, mainly fruit juices, and of cola beverages were significantly associated with elevated risks of fractures [for an increase of one-half can per day, the odds ratios and associated 95% confidence intervals were 1.6 (1.2 to 2.3) and 1.7 (1.2 to 2.6) respectively]. In the absence of other common elements between cola and non carbonated beverages the positive associations of these beverages, with bone fractures probably reflect the increased rehydration needs of active children who are also at high risk for injuries.

Bone mineral density, muscle strength and physical activity. A population-based study of 332 subjects aged 15-42 years

The aim of this population-based study was to find out whether differences in levels of physical activity have an influence on bone mass quantity and whether quadriceps muscle strength is a reliable determinant of bone mass. Included were 175 men and 157 women, aged 15-42 years. Bone mineral density (BMD) was measured at various sites by dual X-ray absorptiometry (DXA) and single photon absorptiometry (SPA). Muscle strength was assessed using an isokinetic muscle force meter. A questionnaire was used to estimate the level of physical activity. We found a positive correlation between physical activity and BMD for boys at the distal forearm and for girls at the trochanter (age group 15-16 years). Active men (age group 21-42 years) had up to 9% higher BMD levels at the hip than those who were less active. Quadriceps muscle torque was not an independent predictor of BMD. Our data suggest that a higher level of physical activity-within the limits of a "normal life style"-may have a positive effect on BMD in the proximal femur of young adults, which in turn may lessen the subsequent risk of fracture.

Calcium-enriched foods and bone mass growth in prepubertal girls: a randomized, double-blind, placebo-controlled trial

High calcium intake during childhood has been suggested to increase bone mass accrual, potentially resulting in a greater peak bone mass. Whether the effects of calcium supplementation on bone mass accrual vary from one skeletal region to another, and to what extent the level of spontaneous calcium intake may affect the magnitude of the response has, however, not yet been clearly established. In a double-blind, placebo-controlled study, 149 healthy prepubertal girls aged 7.9+/-0.1 yr (mean+/-SEM) were either allocated two food products containing 850 mg of calcium (Ca-suppl.) or not (placebo) on a daily basis for 1 yr. Areal bone mineral density (BMD), bone mineral content (BMC), and bone size were determined at six sites by dual-energy x-ray absorptiometry. The difference in BMD gain between calcium-supplemented (Ca-suppl.) and placebo was greater at radial (metaphysis and diaphysis) and femoral (neck, trochanter, and diaphyses) sites (7-12 mg/cm2 per yr) than in the lumbar spine (2 mg/cm2 per yr). The difference in BMD gains between Ca-suppl. and placebo was greatest in girls with a spontaneous calcium intake below the median of 880 mg/d. The increase in mean BMD of the 6 sites in the low-calcium consumers was accompanied by increased gains in mean BMC, bone size, and statural height. These results suggest a possible positive effect of calcium supplementation on skeletal growth at that age. In conclusion, calcium-enriched foods significantly increased bone mass accrual in prepubertal girls, with a preferential effect in the appendicular skeleton, and greater benefit at lower spontaneous calcium intake.

The influence of family history of hip fracture on the risk of vertebral deformity in men and women: the European Vertebral Osteoporosis Study

There are few data exploring clustering of osteoporotic fractures within families. The aim of this study was to determine the influence of maternal and paternal history of hip fracture on the risk of vertebral deformity. 12,816 men and women aged 50 to 75 years were recruited from population based sampling frames across Europe. Subjects were invited to attend by letter of invitation for an interviewer administered questionnaire and lateral spinal radiographs. Vertebral deformity was defined morphometrically using the McCloskey-Kanis method. 6.4% of men and 7.1% of women reported that their mother had suffered a hip fracture, while 1.7% of both men and women reported that their father had suffered a hip fracture. A maternal history of hip fracture was associated with a modest increased risk of vertebral deformity in men [odds ratio (OR) 1.3, 95% confidence interval (CI) 1.0-1.8], the risk being greater among those aged 65 years and over (OR = 1.5; 95% CI 1.0-2.4) and in those from low prevalence areas. There was no increased risk in women. Paternal history of hip fracture was not associated with vertebral deformity in either sex. In conclusion, maternal history of hip fracture appears to be a risk factor for vertebral deformity, particularly in men.