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

High-impact exercise promotes bone gain in well-trained female athletes

Maximizing peak bone mass, as well as reducing its loss after menopause, is important for the prevention of osteoporosis. One mode of activity, gymnastics training, invokes high impact loading strains on the skeleton which may have powerful osteogenic effects. To examine the role of athletic activity, specifically gymnastics, on bone mineral density (BMD) accretion, we monitored longitudinal changes in regional and whole body BMD in collegiate women gymnasts and competitive athletes whose skeletons are exposed to differential loading patterns: runners and swimmers. Two cohorts were studied. Cohort I = 26 gymnasts (19.7 +/- 1.2 years), 36 runners (21.1 +/- 2.7 years) and 14 nonathletic women (19.3 +/- 1.7 years) followed over an 8-month period. Cohort II = 8 gymnasts (18.9 +/- 1.1 years), 11 swimmers (20.0 +/- 2.3 years) and 11 nonathletic women (19.0 +/- 1.2 years) followed over a 12-month period. Lumbar spine (L2-4), femoral neck, and whole body BMD (g/cm2) were assessed by dual-energy X-ray absorptiometry. For cohort I, the percent change in lumbar spine BMD after 8 months was significantly greater (p = 0.0001) in the gymnasts (2.8 +/- 2.4%) than in the runners (-0.2 +/- 2.0%) or controls (0.7 +/- 1.3%). An increase in femoral neck BMD of 1.6 +/- 3.6% in gymnasts was also greater (p < 0.05) than runners (-1.2 +/- 3.0%) and approached significance compared with controls (-0.9 +/- 2.2%, p = 0.06). For cohort II, gymnasts gained 2.3 +/- 1.6% at the lumbar spine which differed significantly (p < 0.01) from changes in swimmers (-0.3 +/- 1.5%) and controls (-0.4 +/- 1.7%). Similarly, the change at the femoral neck was greater (p < 0.001) in gymnasts (5.0 +/- 3.4%) than swimmers (-0.6 +/- 2.8%) or controls (2.0 +/- 2.3%). The percent change in BMD at any site did not differ between eumenorrheic and irregularly menstruating athletes. These results indicate that bone mineral at clinically relevant sites, the lumbar spine and femoral neck, can respond dramatically to mechanical loading characteristic of gymnastics training in college-aged women. This occurred despite high initial BMD values and was independent of reproductive hormone status. The results provide evidence to support the view that high impact loading, rather than selection bias, underlies high BMD values characteristic of women gymnasts. Because all athletes underwent resistance training throughout the year of study, muscle strengthening activity did not appear to be a significant factor in the skeletal response observed in gymnasts. We conclude that activities resulting in high skeletal impacts may be particularly osteotropic for young women.

Estimated dietary calcium intake and food sources for adolescent females: 1980-92

PURPOSE

To estimate dietary calcium intake of three groups of adolescent females ages 11-12 years, 13-14 years, and 15-18 years during four separate 2-year time periods from the years 1980-92; and to identify their food sources of calcium.

METHODS

Nutrient intake survey based on 14-day food consumption records collected from four national representative samples of 4,000 United States households.

RESULTS

Dietary calcium consumption declined significantly (p < .01) over the 10-year period for the 15-18 year olds. Calcium intake was significantly lower for 13-14 year olds compared to the youngest age group, and for 15-18 year olds when compared to the two younger age groups for all four study periods (p < .01). Over 90% of all adolescent females consumed < 100% of the RDA for calcium during all data collection periods. The percentage of adolescent females who consumed less than two-thirds of the RDA increased with age. Seventy-seven percent of 15-18 year olds consumed below this level from 1990-92. Milk and milk products were the best food sources of calcium contributing over one-half of the calcium to the diet. This percentage declined over time and with age to 44% for the 15-18 year old females in 1990. This drop can be attributed to a 7-12% decline in fluid milk consumption for the 11-12 year olds and 15-18 year olds, respectively.

CONCLUSIONS

Estimates indicate that dietary calcium intakes fall far short of both the Recommended Dietary Allowance (RDA) and National Institutes of Health (NIH) recommendations. Intakes have declined over time, with age, and appear to be related to a decline in fluid milk consumption. Efforts to increase calcium consumption among adolescent females appear critical. Clear recommendations to consume a minimum of three servings everyday of lowfat or nonfat dairy products such as milk and yogurt are needed to help this population meet daily calcium requirements.

Estrogen therapy and osteoporosis: principles & practice

Postmenopausal osteoporosis is linked clearly to estrogen deprivation. Recent research has identified estrogen receptors in bone cells and in other organ systems that help to regulate bone remodeling and calcium homeostasis. Long-term use of estrogen in appropriate doses reduces the risk of hip fractures by 50% to 60% and the risk of vertebral deformation by 90%. This protective effect is maintained as long as estrogen is taken and adequate levels of biologically active estrogen are achieved. Thus, the type, dose, and route of administration of estrogen need to be individualized and the efficacy of treatment monitored by annual bone density testing and selective ultilization of biochemical bone markers. The ability of estrogen therapy to increase bone mass is enhanced by added androgens and progestin therapy, calcium supplementation, and exercise.

Nutrition, genetics and skeletal development

From infancy through young adulthood the activity of bone formation predominates, resulting in a steady accumulation of bone mass. As the rate of growth changes with age, so skeletal modeling progresses through phases of different intensity with time. This is paralleled by concomitant changes in bone and calcium metabolism. Bone modeling and skeletal consolidation probably result from a complex sequence of hormonal changes in interaction with nutritional factors. However, current knowledge of the role, sequence, and genetic regulation of hormonal events during puberty, and of the response of bone tissue in interaction with nutrition is limited. This interaction is now beginning to be elucidated. The importance of this interaction with regard to fracture epidemiology in children and peak bone mass acquisition has been discussed.

Variables related to urinary calcium excretion in young girls

The relations among dietary and calcium kinetic factors and 24-h urinary mineral excretion were evaluated in a group of 89 healthy girls (51 white and 38 black) aged 4.9-16.7 years. Nutrient intakes were calculated for each participant using a weighed intake of all food and beverage on the day of the 24-h urine collection study and two subsequent 24-h food records. A significant relation was noted between urinary calcium and sodium excretion (r = 0.55; p < 0.0001). No significant relations were found between urinary calcium and (a) calcium intake (r = 0.08), (b) protein intake (r = 0.14), or (c) phosphorus intake (r = 0.11). Urinary calcium was not significantly related to fractional calcium absorption (r = 0.03) or net calcium absorption (r = 0.11), but was significantly associated with the bone calcium deposition rate (r = 0.24; p < 0.03). Using a multiple regression model, both urinary sodium and the bone calcium deposition rate were independent predictors of urinary calcium excretion in this population (r = 0.57; p = 0.0001). A substantial number of the children in this population had urinary calcium excretion > 4 mg/kg/day (12%). The incidence of hypercalciuria differed between the racial groups and was markedly higher in the white than in the black children (17.6 vs. 5.3%). Over a range of usual calcium intakes, during the rapid-bone-growth period in childhood and early adolescence, urinary calcium appears relatively unaffected by calcium intake and is most strongly associated with urinary sodium levels.

Bioavailability of calcium of fresh cheeses, enteral food and mineral water. A study with stable calcium isotopes in young adult women

True fractional Ca absorption from six foods was measured in twelve normal healthy women, aged 20-29 years. The tested foods were commercially available fresh cheese, fresh cheese prepared by new technology and rich in Ca, similar cheese with added Fe, enteral food, mineral water alone and combined with a spaghetti meal. The aim of the study was to investigate: (1) Ca absorption from a new Ca-rich fresh cheese and to compare it with that from the traditional commercial type of fresh cheese; (2) the effect of Fe enrichment of the new cheese on Ca absorption; (3) Ca absorption from the mineral water and the enteral product and to compare it with that from the dairy products; (4) the effect of a meal combined with the mineral water on Ca absorption. All test foods were consumed by all subjects according to a design with two Latin squares. Each treatment of 2 d was followed by a wash-out period of 2 weeks. Ca absorption was measured using a double stable-isotope (44Ca and 48Ca) extrinsic labelling technique. Mean fractional Ca absorption from the new fresh cheese was not significantly different from that from the traditional type (37.7 (SD 10.2)% v. 42.2 (SD 11.6)%). The addition of Fe to the new cheese did not significantly influence Ca absorption. Ca-absorption values from the mineral water (37.0 (SD 9.8)%) and from the enteral product (42.6 (SD 11.4)%) were not significantly different from those from the dairy products (37.7-42.2%, SD 10.2-11.6%). The co-ingestion of a spaghetti meal with the mineral water significantly enhanced Ca absorption from 37 (SD 9.8)% to 46.1 (SD 11.7)%. It is concluded that a new process leading to a fresh cheese with a higher Ca concentration does not alter Ca bioavailability compared with the standard technology and for a constant Ca supply. Thus this new fresh cheese would probably provide more Ca than the standard one. The fractional Ca-absorption values for mineral water and the enteral product indicate that these products can make an interesting contribution to Ca supply for populations with a low Ca intake and patients with specific diseases respectively.

Bone mineralization and bone mineral metabolism in children with juvenile rheumatoid arthritis

OBJECTIVE

To identify mechanisms of the osteopenia associated with juvenile rheumatoid arthritis (JRA) by determining parameters of bone mineralization, and bone mineral content and density (BMC and BMD), in children with JRA.

METHODS

BMC and BMD were measured by dual x-ray absorptiometry in 41 children with JRA and 62 healthy children. Serum samples were analyzed for concentrations of minerals, vitamin D, parathyroid hormone, osteocalcin, bone-specific alkaline phosphatase (BAP), procollagen I carboxy-terminal propeptide, and tartrate-resistant acid phosphatase (TRAP), and urinary excretion of deoxypyridinoline crosslinks and calcium.

RESULTS

BMD was decreased in all sites in JRA patients. BMD, corrected for age, height, weight, and bone area, was decreased at cortical bone sites (1/3 radius, upper and lower extremities, and whole body). Low concentrations of osteocalcin and BAP suggested reduced bone formation, and low TRAP levels suggested decreased resorption. Clinical scales of disease severity were negatively correlated with measures of bone mass. Laboratory markers of disease severity were highly correlated with decreases in markers of bone formation, but not with those of resorption. Although laboratory findings were similar for children with oligoarticular and polyarticular disease, differences in bone mass were greater in children with polyarticular disease.

CONCLUSION

These data suggest an association between decreased bone mineralization in JRA and low bone formation that is related to disease severity. Efforts to stimulate bone formation, therefore, need to be considered clinically in prepubertal children with active JRA.

Importance of participation rate in sampling of data in population based studies, with special reference to bone mass in Sweden

OBJECTIVE

To study the effects of participation rate in sampling on "normative" bone mass data.

DESIGN

This was a comparison between two randomly selected samples from the same population. The participation rates in the two samples were 61.9% and 83.6%. Measurements were made of bone mass at different skeletal sites and of muscle strength, as well as an assessment of physical activity.

SETTING

Malmö, Sweden.

SUBJECTS

There were 230 subjects (117 men, 113 women), aged 21 to 42 years.

RESULTS

Many subjects participated in both studies (163). Those who took part only in the study with the higher participation rate (67) almost invariably had higher values for bone mass density at the sites measured (up to 7.6% for men) than participants in the study with the lower participation rate. No differences in muscle strength were recorded.

CONCLUSION

A high degree of compliance is important to achieve a reliable result in determining normal values in population based studies.

Dietary sources of calcium and the contribution of flour fortification to total calcium intake in the diets of Northumbrian adolescents

Increased Ca intake by adolescents is desirable. In order to achieve this, information on the current dietary sources of Ca by this age group is essential to enable change to build on existing habits. This paper addresses two issues: first, the dietary sources of Ca for adolescents are reported and, second, the importance of fortification of flour with Ca to present-day Ca intakes was determined. In 1990 the diets of 379 children aged 12 years were assessed using the 3 d dietary diary and interview method. Computerized food tables were used to calculate the contributions of different food groups to total Ca intake. The Ca content of each food was subdivided into naturally occurring Ca and Ca from fortification, and data were analysed to give the daily intake of each. The four most important sources of Ca were milk (25%), beverages (12%), puddings (10%) and bread (9%). Fortification of flour accounted for 13% of total Ca intake. When the contribution of fortification was removed, the proportion of subjects with intakes of Ca below the lower reference nutrient intake (Department of Health, 1991) increased more than fourfold, to 10% of girls and 12% of boys. Milk is contributing less to Ca intake than in the past and increased consumption should be encouraged. Ca fortification of flour remains an important source of Ca. Therefore, unless dietary habits are modified to ensure adequate Ca from other sources, increased consumption of unfortified products from outside the UK will lead to a further reduction in Ca intake.

Roles of diet and physical activity in the prevention of osteoporosis

In recent years, much attention has been directed toward the prevention of osteoporosis, since this disease has become a leading cause of morbidity and mortality in elderly women. Research has demonstrated that the prevention of osteoporosis and osteoporosis-related fractures may best be achieved by initiating sound health behaviors early in life and continuing them throughout life. Evidence suggests that osteoporosis is easier to prevent than to treat. In fact, healthy early life practices, including the adequate consumption of most nutrients, regular physical activity, and other health behaviors, contribute to greater bone mineral measurements and optimal peak bone mass by the fourth decade of life of females, and, perhaps, also of males. Several reports have shown that the adequate consumption of nutrients, calcium in particular, during the pre-pubertal and early post-pubertal years of females contribute to increased peak bone mass. Indeed, skeletal benefits from long-term calcium supplementation have been reported for females at practically every period of the life cycle. Vitamin D, which may be either consumed or produced endogenously through the action of sunlight, promotes calcium absorption and thereby enhances bone mineralization. Thus, the adequate consumption of calcium, in conjunction with vitamin D, in early life will likely optimize peak bone mass, and adequate intakes of these two nutrients should continue through the remainder of life to help maintain bone mass. On the other hand, excess phosphorus consumption may deter bone mineral accrual because of the resultant elevation of serum parathyroid hormone levels. Additionally, high intakes of protein, sodium, and caffeine may decrease bone mineral mass through increased urinary excretion of calcium. Vitamin K may also have an important positive effect on the development and maintenance of bone through its role in promoting carboxylations of the matrix protein, osteocalcin. In conclusion, the prevention of osteoporosis needs to begin during the pre-pubertal years and it should be continued throughout life. Bone mass can better be maintained later in life through adequate consumption of several nutrients with specific roles in calcium and bone metabolism, regular physical activity, and the practice of a healthy lifestyle. Mechanisms through which the nutrients and exercise affect bone mass will be explored.

Physical activity and dietary constituents as predictors of forearm cortical and trabecular bone gain in healthy children and adolescents: a prospective study

We have prospectively studied forearm trabecular and cortical bone mineral density gain (delta BMD) in relation to nutrient intake, weight-bearing physical activity (WPA) and daylight exposure (DE) in 470 healthy boys and girls aged 8.2-16.5 years at the baseline. BMD was assessed using single photon absorptiometry (SPA). Cortical delta BMD peaked at the age of 14.0 +/- 0.3 and 16.0 +/- 0.3 (SD) years in girls and boys, respectively. Girls had achieved adult premenopausal values of trabecular BMD by the age of 15 years and cortical BMD values by the age of 16.5 years. WPA, BMD, body height, height gain, weight, weight gain, dietary polyunsaturated fat and sodium were correlated with delta BMD. WPA, predicting cortical as well as trabecular delta BMD, had the greatest effect on trabecular delta BMD in the presence of a high calcium intake in children below 11 years of age. In conclusion, our results indicate that physical activity and calcium intake should be encouraged at a prepubertal age in order to increase bone density.

Effects of age, sex, and heredity on measures of bone mass in baboons (Papio hamadryas)

Bone mass and bone density were estimated in 219 pedigreed baboons (Papio hamadryas) by radiographic morphometry of the left second metacarpal. Compact bone width (total bone width--medullary canal diameter) and bone ratio (compact bone width/total bone width) decreased with increasing age squared in both sexes. The heritability of medullary canal diameter was 0.64 +/- 0.11, of compact bone width was 0.40 +/- 0.15 and of bone ratio was 0.67 +/- 0.13. The results indicate baboons are a useful model for studies of age, sex and genetic effects on bone mass.

Segregation analysis and variance components analysis of bone mineral density in healthy families

Bone mineral density (BMD) was measured in 1992-93 in 129 nuclear families, including 258 parents and 183 children, and was analyzed for familial resemblance factors. BMD measurements were adjusted on weight and age. Segregation analysis rejected the monogenic hypothesis and exhibited a strong polygenic component. Variance components analysis was then used to estimate the parameters of a multivariate normal model including an additive polygenic component, a common environment factor, and a residual specific to each individual. The genetic component was independent of sex and age. The common environmental factor was not significant. The variance of the residual specific factor appeared to be a quadratic function of age, reaching its minimum value at 26.4 years. Consequently, the maximum value for heritability (ratio of genetic variance to total variance) is observed at this age (h2 = 0.84). According to this model, the correlation between two relatives is a function of the ages of each individual in the pair.

Bone mineral content of young female former gymnasts

Intense physical exercise and diet restriction could result in delayed puberty and have a negative influence on the acquisition of peak bone mass during puberty. Nineteen young women who had been in elite gymnastic training during their prepubertal and pubertal years were investigated with regard to their health, menstrual data and bone mineral areal mass (BMA). Twenty-one women of comparable age served as controls. The age of menarche of the "former" gymnasts and the controls was 14.8 +/- 1.8 and 12.1 +/- 1.4 years, respectively. Fourteen of the gymnasts had been or were using oral contraceptives (OCs) and most of the non-users now had regular menstrual periods. During the years preceding the study, physical activity among the "former" gymnasts had gradually declined. Although the gymnasts had had a delayed puberty, no difference was found in total body or spinal BMA compared to the healthy controls. Their normal BMA in early adulthood could reflect a catch-up due to a combination of decreasing athletic activity, normal menstrual cycles and intake of OCs.

Bone mineral metabolism in children with juvenile rheumatoid arthritis

Osteopenia has emerged as a major determinant of the outcome of children with juvenile rheumatoid arthritis. Although vertebral compression fractures and fractures of long bones were recognized historically as important clinical developments in the course of disease, a decrease in skeletal mass could only be quantitated and documented early in disease by the recent introduction of bone absorptiometry. This article is limited to recent data from studies on osteopenia in juvenile rheumatoid arthritis and suggests directions of future research that have relevance to current unanswered questions in prevention or management.

Bone metabolism and osteopenia in eating disorders

Bone loss is a potentially debilitating condition in women with eating disorders. Complications may include failure to achieve peak bone mass, increased risk of premature fractures, and inability to reach the height potential. We therefore conducted a comprehensive evaluation of 58 women with anorexia nervosa (AN), bulimia (BUL) and anorexia/bulimia (AB), comparing bone mineral density (BMD) to physical parameters, biochemical indices, and markers for bone formation and resorption. BMDs were significantly lower in patients with AN than in those with AB and BUL, and overt osteopenia was uncommon in AB and BUL. Hypercortisolism was the best laboratory marker to assess the risk of osteopenia in patients with AN. However, there were no associated changes in bone formation or resorption parameters. No direct correlation was found between BMD and body mass index, estrogen deficiency, tubular reabsorption of phosphorus, serum vitamin D, PTH, BGP, or alkaline phosphatase levels. Although the prognosis for complete recovery to normal BMD is poor, treatment of the underlying depressive disorder, improvement in nutrition with increased weight, and spontaneous resumption of menses are associated with restoring bone health.

Role of calcium and vitamin D in the prevention and the treatment of postmenopausal osteoporosis: an overview

When discussing the use of calcium and vitamin D in the prevention and the treatment of osteoporosis one can make a distinction between the use as dietary supplementation to correct or prevent deficiencies, and the pharmacologic use of higher doses, whether or not in association with other drugs. However, in practical terms it is not always possible to clearly make this distinction. Available evidence suggests that increasing the calcium intake can favourably affect the build-up of bone mass in adolescence. In this population, the daily consumption of calcium in the diet should, optimally, be at least 1200 mg/day. In view of the lack of data pertaining to the effect on the final peak bone mass, there is at present time no basis for the systematic administration of calcium supplements to healthy children and adolescents. Calcium supplementation, aiming at a total calcium intake of at least 1500 mg/day, has a partial protective effect on postmenopausal bone loss, this effect being documented mainly in women more than 5 years after menopause. In the present state of our knowledge, there is no established role for vitamin D supplementation in the prevention of postmenopausal osteoporosis, except in elderly patients presenting with a higher risk for relative vitamin D deficiency and with low calcium intake. The results of a controlled trial suggest that in institutionalised elderly patients, systematic administration of calcium and vitamin D supplements can substantially reduce the risk of hip fracture. In the treatment of established postmenopausal osteoporosis, calcium supplementation has only a role as a general adjuvant therapeutic measure and as a specific complement to the treatment with other active compounds. There are indications that treatment alpha-calcidol or calcitriol has a positive effect on the evolution of bone mass, but awaiting further confirmation of a favourable effect on the incidence of osteoporotic fractures, treatment with these drugs remains experimental.

Osteoporosis as a pediatric problem

Osteoporosis has long been considered a disease of the elderly; however, there is now a general agreement that predisposition begins in childhood and adolescence; thus, rational approaches to prevention of the disease should be started during childhood and adolescence. Indeed, by determining PBM, events occurring in the first two decades of life may determine in large part the subsequent risk of osteoporosis. Attention has thus been focused on the physiology of bone mass accumulation during growth, including the role of environmental factors such as dietary calcium and exercise. Because their patients are at this particular time of life, when PBM is being achieved, pediatricians are in a critical position to affect changes in the long-term risk of osteoporosis in their female and male patients.

Precise determination of the absorptive component of urinary calcium excretion using stable isotopes

Some patients with hypercalciuria are thought to have enhanced enteric calcium absorption, with a major component of recent diet contributing to urinary calcium. This mechanism has been difficult to test with the usual calcium loading procedures. We employed dual stable calcium isotope tracers to quantitate the components of urinary calcium excretion in 38 healthy female children. The mean urinary calcium excretion in these girls was 2.4 mg/kg per day. The contribution of recent diet to this total was a mean of 0.2 mg/kg per day. The maximum dietary contribution to urinary calcium excretion was 0.86 mg/kg per day. Recent diet contributes a mean of 8% to total dietary calcium excretion. This novel method permits precise quantitation of the contributions of recent diet and tissue stores to urinary calcium excretion. In these healthy girls, the fraction of urinary calcium derived from diet is trivial.

Micronutrients and exercise: anti-oxidants and minerals

Exercise has been shown to increase indirect measures of lipid peroxidation. However, exercise and training appear to augment the body's anti-oxidant defence system. Whether this augmented defence system can keep up with the increase in lipid peroxidation with exercise is not known. Iron depletion is experienced by many athletes, especially female endurance athletes and adolescents, but iron deficiency anaemia is rare. Iron depletion could affect the ability to train and recover from strenuous exercise, but this has not been examined. There is a concern that female athletes, especially adolescents, are not ingesting sufficient calcium, and this may affect the development of peak bone mass and increase the risk of bone fractures. Further research is needed on mineral and trace mineral intake and loss in athletes. It appears that most athletes have adequate status of chromium, zinc, phosphate and magnesium. Athletes who are restricting energy intake to achieve a low body mass (for example, endurance runners), may not have adequate vitamin or mineral status. More data are needed on vitamin/mineral status of athletes from underdeveloped countries. The general recommendation for athletes is that foods rich in anti-oxidants and minerals should be ingested rather than supplements.

Dieting attitudes and behavior in urban high school students: implications for calcium intake

PURPOSE

Adolescence is a time of rapid gain in bone density which may be influenced by calcium intake. This study assessed whether dieting concerns, known to be prevalent in adolescent girls, were associated with the calcium intake of adolescents of varying ethnicity.

METHODS

Students (n = 856) completed an instrument which assessed current weight, desired weight, height, age, ethnicity, calcium intake using a food frequency questionnaire, dieting concerns using the Eating Attitudes Test dieting subscale (DS), taste enjoyment of dairy products, and type of milk consumed.

RESULTS

Among 782 students with useable responses, most girls (69.1%) wanted to lose weight and most boys (54.2%) wanted to gain weight. Asian girls had lower body mass index (BMI) than Caucasians (19.3 +/- 2.1 vs 20.8 +/- 2.6 kg/m2, p < 0.05), but desired BMI did not vary by ethnicity in either girls or boys. Asian girls also had lower DS scores than Caucasians, but the difference was not significant with current BMI as a covariate. Girls' DS scores were higher than those of boys (6.3 +/- 6.5 vs 2.3 +/- 3.2, p < 0.001), and estimated calcium intakes were lower (815 +/- 528 vs 1149 +/- 701 mg/day, p < 0.001); however, DS scores were not associated with calcium intake for either sex. Especially among girls, dieting and body size concerns were associated with taste enjoyment of certain dairy products, and with the type, but not the amount, of milk consumed. Girls using skim milk had higher DS scores than those using low-fat or whole milk.

CONCLUSIONS

In this non-clinical sample, greater concern about dieting and body size did not directly compromise calcium intake but was associated with the type of milk used.

Physical activity, calcium intake, and bone mineral content in children in The Netherlands

STUDY OBJECTIVE

To examine the relation between physical activity, calcium intake, and bone mineral content in children.

DESIGN

Population based, cross sectional study.

SETTING

Primary schools in Zoetermeer, The Netherlands.

PARTICIPANTS

Altogether 1359 Dutch boys and girls, aged 7 to 11 years (response rate 88%).

MEASUREMENTS

Bone mineral content was measured by quantitative roentgen microdensitometry of the midphalanx of the second digit at the diaphyseal and metaphyseal site. Maximal exercise testing, according to the Bruce treadmill protocol, was used to assess physical fitness. Habitual physical activity was assessed by use of a questionnaire on physical activities. Daily calcium intake from dairy products was estimated by use of a semiquantitative food frequency questionnaire.

MAIN RESULTS

Bone mineral content in boys was not linearly associated with physical fitness after adjustments for differences in height, body weight, chronological age, and skeletal age. In girls a linear association was found at the metaphyseal site only. When extreme groups were compared, bone mineral content was found to be higher in "high fitness children" (upper decile) than "low fitness children" (lowest decile), with statistical significance reached in boys only. When analyses were performed in subgroups of skeletal age, a clear linear relation between physical fitness and bone mineral content was seen in the mature subgroup in both boys and girls. No linear association was found between habitual physical activity and bone mineral content, while the results in extreme groups (that is, upper versus lowest decile) and in subgroups of skeletal age were comparable to those on physical fitness in boys only. No association was found between daily calcium intake and bone mineral content in this age group.

CONCLUSIONS

This cross sectional study in children aged 7 to 11 years suggests that an increased bone mineral content is found only in those with a high level of physical activity. This association is most pronounced in the more mature children. No evidence was found for an association between daily calcium intake and bone mineral content in childhood.

Bone mineral density in adolescents

Bone densitometry is becoming more widely available and is no longer limited to studying the elderly. Rapid, safe, and accurate methods of measuring BMD now allow serial determination of this important factor in fracture risk and will undoubtedly become even more accessible in the future. Likewise, our knowledge about the mechanisms and genetics of bone resorption and bone formation is rapidly expanding. Therefore, efforts to prevent osteoporosis in later life by maximizing peak BMD during adolescence and young adulthood must be directed at identifying young people who are at risk because of low body weight, inactivity, inadequate calcium intake, sex hormone deficiency, or because of disease or treatments associated with reduction of BMD. If BMD is found to be low, efforts to enhance bone formation (eg, weight gain, weightbearing exercise, increased calcium intake, and effective treatment of the underlying illness) should be encouraged. Antiresorptive agents, such as sex hormones, should be used cautiously, since they can have significant side effects and may not produce the expected results. Pediatricians must keep in mind the axiom: osteoporosis ... the only cure is prevention.

Influence of spontaneous calcium intake and physical exercise on the vertebral and femoral bone mineral density of children and adolescents

Peak bone mass is determined mainly by genetic-ethnic factors, but environmental factors such as calcium intake and physical activity during childhood and adolescence could play a role. We have measured the bone mineral density (BMD) of 151 healthy children and adolescents, ages 7-15.3 years. Density was measured by dual X-ray absorptiometry (DXA) at two sites (lumbar verterbrae L1-L4 and the upper femur), and the data were analyzed in terms of the height, weight, sexual maturation, spontaneous calcium intake, and physical activity. Of the children, 57-71% had calcium intakes below 1000 mg/day. BMD increased with pubertal maturation from 0.68 +/- 0.08 to 0.92 +/- 0.09 g/cm2 (vertebral bone density, VBD) and from 0.87 +/- 0.10 to 1.03 +/- 0.09 g/cm2 (femoral bone density, FBD) between Tanner stage 1 and 5. Multiple regression analysis showed that body weight and Tanner stage were main determinants of bone density when expressed as g/cm2. The weekly duration of sports activity also influenced both the vertebral (p < 0.001) and femoral (p = 0.01) sites, especially in girls and during puberty. Dietary calcium appeared to be another independent determinant of BMD, especially before puberty, at the vertebral (p = 0.02) site. Most important, dietary calcium was found to be the main determinant of vertebral mineral density, when expressed as z score, in both sexes. Moreover, 93% of the 28 children with low vertebral z score values (below -1) and 84% of the 31 children with low femoral z score values (below -1) had dietary calcium intakes below 1000 mg/day.

Relative rates of fracture of the hip in the United States. Geographic, sex, and age variations

We studied the Medicare data from 1984 through 1987 for 687,850 fractures of the hip that had occurred in the United States. Our purpose was to determine the geographic, sex-specific, and age-interval variations in the relative risk of fracture of the hip in elderly white individuals. The rates of cervical, trochanteric, and subtrochanteric fracture, and the over-all rate of fracture at any of the three levels, increased with age, were greater for women than for men, and were higher in the Southern part of the country. However, there were regional, sex, and age variations. The ratio of cervical to trochanteric fractures was significantly higher in the East South Central region and lower in the Middle Atlantic and New England regions (p < 0.05). These were the same areas with the highest and lowest over-all rates, respectively, of fracture of the hip. The ratio of cervical to trochanteric fractures decreased from 1.52 in women who were sixty-five to sixty-nine years old to 0.81 in women who were at least eighty-five years old, but it stayed at approximately 1.00 for the corresponding age-groups of men. The ratio of fracture of the hip in women to fracture of the hip in men varied depending on the level of the fracture.

Dietary calcium, saturated fat, fiber and vitamin C as predictors of forearm cortical and trabecular bone mineral density in healthy children and adolescents

Diet, weight-bearing physical activity (WPA) and daylight hours spent outdoors (DE) were related to bone mineral density in the distal (BMDd) and ultradistal (BMDud) forearm of 495 healthy children (8-11 years) and adolescents (11-17 years). BMD was assessed by single photon absorptiometry. Using multiple regression, BMDd was predicted by saturated fat and BMDud by fiber in children. In adolescents, BMDd was predicted by saturated fat and vitamin C, and BMDud by calcium and vitamin C. WPA and DE were not related to BMD. In conclusion, our results showed that current intake of calcium, saturated fat, fiber and vitamin C were positively associated with forearm BMD in children and adolescents. These associations depended on age and bone type. If our findings are verified, dietary recommendations, especially when aimed at young people, may have to be reconsidered.

Effects of dairy products on bone and body composition in pubertal girls

OBJECTIVE

To study the effect of calcium supplementation with dairy products on the bone and body composition of pubertal girls.

DESIGN

Randomized control study with 12-month follow-up.

SETTING

General community.

SUBJECTS

Forty-eight white girls whose mean age was 11 years and sexual development at Tanner stage 2.

INTERVENTION

One group's diet was supplemented with dairy products to the recommended dietary allowance of 1200 mg calcium daily. The other group ate their usual diet.

MAIN OUTCOME MEASURES

Bone mineral content and density were measured at the radius, femoral neck, lumbar spine, and total body bone mineral by single-photon and dual-energy x-ray absorptiometry at the start of the study and after 3, 6, 9, and 12 months. Body composition (lean body mass and body fat) was measured by dual-energy x-ray absorptiometry at the same intervals. Serum calcium, phosphate, 25-hydroxyvitamin D, 1,25-dihydroxyvitamin D, alkaline phosphatase, magnesium, and albumin concentrations were determined at the start and end of the study. The urinary calcium/creatinine ratio and hydroxyproline concentration were also determined.

RESULTS

The dairy group had higher intakes of calcium, phosphate, vitamin D, and protein than control subjects. The dairy group had significantly greater increases during the 1-year study in bone mineral density at the lumbar spine bones (22.8% +/- 6.9% vs 12.9% +/- 8.3%) and in total body bone mineral (14.2% +/- 7.0% vs 7.6% +/- 6.0%) than control subjects. Dietary calcium, phosphate, vitamin D, and protein intakes were associated with the lumbar bone density and total body bone calcium. There were no differences in serum or urinary biochemical values between the two groups at the start or end of the study.

CONCLUSIONS

Young girls whose dietary calcium intake was provided primarily by dairy products at or above the recommended dietary allowances had an increased rate of bone mineralization. Increased intake of dairy foods did not increase overall total or saturated fat intake and was not associated with excessive weight gain or increased body fat.

Bone density in young women is associated with body weight and muscle strength but not dietary intakes

Potential determinants of bone mineral density (BMD) were studied cross-sectionally in 115 healthy, sexually mature Caucasian women aged 18 years. Bone mineral density (Hologic QDR1000W) of the lumbar spine, proximal femur (five sites), and distal tibia and fibula; fasting blood and urine calcium biochemistry; serum sex hormone levels (follicular phase); nutrient intakes; aerobic fitness; trunk muscle strength; and habitual activity levels were measured. The effects of heredity were considered by measuring the BMD of 107 of the subjects' mothers. Simple and stepwise regression analysis were used to identify significant determinants of BMD at each of the regions studied. The analysis indicated that significant bivariate correlations exist between BMD at all sites and body weight (r = 0.23-0.47, p < or = 0.01), lean body weight (r = 0.34-0.46), trunk strength (r = 0.27-0.47), physical activity score (r = 0.20-0.25), and aerobic fitness (r = 0.29-0.45). Dietary calcium intake correlated significantly with BMD at the trochanter site only (r = 0.19), and none of the biochemical or hormonal indices measured correlated consistently with BMD at any site. Significant correlations between the BMD of mothers and daughters ranged from r = 0.43 at lumbar spine to r = 0.34 at the intertrochanteric site. Paired t-tests showed the daughters had significantly (p < 0.03) lower BMD than their mothers at the lumbar spine (98 +/- 12% [mean +/- SD]) and significantly higher (p < 0.002) BMD at the femoral neck, trochanter, and total hip sites (110 +/- 16%, 108 +/- 17%, 103 +/- 14%, respectively). When stepwise regression analysis included weight-corrected strength of the trunk flexor muscles (Corr Flex), weight-corrected aerobic fitness (Corr VO2max), physical activity score, and body weight, body weight was the only significant determinant of BMD at all sites. Corr Flex made significant contributions at all sites except the femoral neck, while Corr VO2max made additional contribution at the femoral neck, trochanter, total hip, and shaft of femur sites. These variables accounted for 13-27% of the variance in BMD. The addition of mother's BMD to these independent variables, in stepwise regression analysis, improved the prediction to 18-31% of the variance.

Effects of double-blind controlled calcium supplementation on calcium absorption in Chinese children measured with stable isotopes (42Ca and 44Ca)

A double-blind controlled Ca supplementation trial was conducted for 6 months in thirty-four 7-year-old Chinese children from Hongkong and Jiangmen, China. The children were randomly allocated to the study group (n 17) or control group (n 17), and a CaCO3 tablet (300 mg Ca) or a placebo tablet was taken daily. True fractional Ca absorption (TFCA) was evaluated before and after the trial using stable isotopes: 8 mg 44Ca mixed in 100 g chocolate milk was given after an intravenous injection of 0.75 mg 42Ca. There was no significant difference in baseline TFCA between the study group (60.6 (SD 11.4)%) and the controls (58.2 (SD 9.0)%; P = 0.55). Serum 25-hydroxycholecalciferol levels were comparable between the two groups (P = 0.71). After 6 months, TFCA of the study group (55.6 (SD 12.7)%) was significantly lower than that of the controls (64.3 (SD 10.7)%; P = 0.015). By comparing the individual changes in TFCA after the trial between the two groups there was a non-significant reduction in TFCA (5.03 (SD 12.4)%; P = 0.11, Wilcoxon signed-rank test) in the study group (60.6-55.6%), whereas a significant increase in TFCA (6.17 (SD 7.7)%; P = 0.004, Wilcoxon signed-rank test) was observed in the controls (58.2-64.3%). The differential in TFCA between the two groups after 6 months was significantly different (P = 0.001), and remained significant after adjustment for baseline dietary intakes, weight and height by multiple-regression analysis (P = 0.003). If the mechanism of TFCA from chocolate milk in response to the treatment effects is similar to that from the total diet, then our results suggest that children with adequate vitamin D status can adapt to a change in Ca intake by adjusting the efficiency of TFCA. In corollary, children on habitually-low Ca diets have a higher TFCA than the counterparts with higher Ca diets.

Dietary factors related to preservation of oral and skeletal bone mass in women

Skeletal bone loss in adults increases the risk of bone fractures and may contribute to the loss of teeth in healthy postmenopausal women. The relationship of skeletal osteopenia to residual ridge resorption is unclear. Low bone mass in women is attributed to heredity, estrogen deficiency, a low lifetime calcium intake, and lack of regular physical activity. A high calcium intake will promote optimal bone growth in youth and decrease the rate of bone loss in the later postmenopausal period. In early menopause, estrogen is the only effective therapy for conserving bone in women. In older women, a high plasma level of vitamin D enhances calcium absorption, whereas high sodium, protein, alcohol, and caffeine intakes will cause increased urinary losses and negative calcium balance. Women who have a low intake of dairy foods may benefit from a refined calcium carbonate supplement that contains vitamin D. This article focuses on the nutritional factors that influence bone health.

Environmental and genetic factors affecting bone mass. Similarity of bone density among members of healthy families

OBJECTIVE

To evaluate the relative importance of environmental and genetic factors in the determination of bone mineral density (BMD) and to quantify the risk of low BMD in healthy young adults in relation to the BMD of their parents.

METHODS

Dual-energy x-ray absorptiometry study of a series of 129 nuclear families (441 subjects), including 183 children over age 15, was performed. Correlation of BMD in children with BMD in their parents was studied in a linear model, taking into account environmental factors. Logistic regression was used to quantify the relative risk of lower BMD according to the parents' BMD level.

RESULTS

BMD was significantly correlated with weight, height, and body mass index (BMI) in all family members, and with parents' alcohol consumption and with physical activity in fathers and sons. The BMD of the children correlated with that of their parents (r = 0.27). The child's BMI, his/her father's BMD and daily calcium intake, and his/her mother's BMD, BMI, and body fat accounted for 41.4% of the variance in the child's BMD. A son had a 3.8 times higher risk of having a low BMD if his father had a low BMD, and a daughter had a 5.1 times higher risk if her mother had a low BMD.

CONCLUSION

The BMD of children in healthy families was related to the BMD of their parents as well as to environmental factors, confirming the contribution of genetic inheritance in the determination of bone density in young adults, especially in girls.

Exercise considerations for postmenopausal women with osteoporosis

Individuals with osteoporosis are at an increased risk of fracture due to a net loss of bone mass. The cellular mechanisms causing decreased bone mass are increased osteoclast-mediated bone resorption and/or decreased osteoblast-mediated bone formation. Clinical studies have shown that bone loss can be prevented by estrogen replacement therapy and calcium supplementation. Weight-bearing and strengthening exercise may also play a role in retarding bone loss in the postmenopausal woman, and it may even increase bone mass. The essential components of an exercise program include intensity, duration, frequency, and type of activity. Additional goals of a therapeutic exercise program are to improve flexibility and balance, and to prevent falls. Structure-function relationships in normal and osteoporotic bone and the effects of exercise on bone are reviewed. A rational approach for exercise strategies is discussed.

True fractional calcium absorption in Chinese children measured with stable isotopes (42Ca and 44Ca)

True fractional Ca absorption (TFCA) was compared in children with different habitual Ca intakes using a double-label stable-isotope technique. Chinese children aged 7 years from Hongkong (n22) and Jiangmen (n12) participated in the study. An oral administration of 8 mg 44Ca in 100 g chocolate milk was given shortly after an intravenous injection of 0.75 mg 42Ca. Ca isotopic ratios were determined in urine samples collected 24 h later using thermal-ionization mass spectrometry. There was no significant difference in TFCA between Jiangmen and Hongkong children (P = 0.16). TFCA of a lower-Ca-intake group (Ca < or = 500 mg/d, n19) with mean Ca intake 359 mg/d was 63.1 (SD 10.7)% and that of a higher-Ca-intake group (Ca > 500 mg/d, n15) with mean Ca intake 862 mg/d was 54.8 (SD 7.3)%; the difference in TFCA was significant (P = 0.016). Serum levels of 25-hydroxycholecalciferol of the children were adequate (33.7 (SD 7.7) ng/ml). The present study indicates that growing children accustomed to a low-Ca diet appear to be able to enhance their absorptive capacity. If it is assumed that dietary Ca absorption by Chinese children resembles their TFCA from a single meal of chocolate milk, then the recommended dietary allowance (RDA) for Ca for Chinese children would be lower than the US RDA (800 mg/d), which is based on an estimated 40% Ca absorption as reported for Caucasian children. A comparative absorption study is necessary to determine whether there is any difference in TFCA between Caucasian and Chinese children.

Bone mineralization in children and adolescents with a milk allergy

To evaluate the correlation between dietary calcium intake and mineralization of the immature skeleton 55 children and adolescents aged 5-14 years (mean, 9.5 years) with a positive radioallergosorbent test (RAST) for serum antibodies to cow's milk protein were evaluated. Bone mineral density (BMD) in the lumbar spine and proximal femurs were measured by dual energy X-ray absorptiometry. BMD at each site for each subject was converted to an age-adjusted Z score based on our own series of 95 normal pediatric controls. Calcium intake was determined using a detailed food frequency questionnaire administered by a nutritionist during a 30-40-min interview. Dietary adjustments to the condition varied and resulted in a wide range of calcium intakes. Calcium supplements were taken by 22% of the subjects and were included in the determination of daily calcium intake. The group of 55 subjects was divided into quartiles based on calcium intake (mean +/- S.E mg calcium/day): Group 1, 409 +/- 21, Group 2, 663 +/- 16, Group 3, 950 +/- 32, Group 4, 1437 +/- 124. Bone density Z scores in the proximal femur serially increased across the calcium intake groups (mean +/- S.E.): Group 1, -0.16 +/- 0.31; Group 2, 0.05 +/- 0.33; Group 3, 0.44 +/- 0.24; Group 4, 0.79 +/- 0.41 (P = 0.03). A similar pattern was found with lumbar spine BMD Z scores: Group 1, -0.16 +/- 0.27; Group 2, 0.10 +/- 0.21; Group 3, 0.18 +/- 0.20; Group 4, 0.30 +/- 0.25 (P = 0.05). These data add further to the evidence that dietary calcium intake is important for optimal mineralization of the growing skeleton.

Universal standardization for dual x-ray absorptiometry: patient and phantom cross-calibration results

The comparison of patient data among different dual x-ray absorptiometry (DXA) scanners is complicated because no universally accepted cross-calibration procedure or standard currently exists. This study was performed under the auspices of the International DXA Standardization Committee to establish appropriate cross-calibration parameters. Posteroanterior (PA) lumbar spine measurements of 100 women, ages 20-80 years (mean 52.6 +/- 16, range of BMD = 0.4-1.6 g/cm2) were obtained on a Norland XR26 Mark II, a Lunar DPX-L, and a Hologic QDR 2000 densitometer using standard procedures (pencil beam mode for all three scanners). Area, BMC, and BMD results from the different scanners were compared for all patients. In addition, the European spine phantom (ESP) and the European spine phantom prototype (ESP prototype), as well as standard phantoms from all three manufacturers, were evaluated on the three systems. To achieve universal scanner calibration, we used the intercept and slope of the patient's correlations and the value of the middle vertebra of the ESP as a reference point in a series of standardization formulas, and we have expressed the results as sBMD (mg/cm2). The correlations of the patients' spinal BMD values were excellent for each of the three scanner pairs. The average absolute difference in patient spinal BMD values (L2-4) between Hologic and Norland was 0.012 g/cm2 (1.3%); it was 0.113 g/cm2 (11.7%) between Hologic and Lunar and 0.118 g/cm2 (12.2%) between Norland and Lunar. The phantoms' regression lines approximated those of the patient regression lines, and the phantoms with only one measurement point were very close to the patients' regression lines. After applying the standardization formulas, the average absolute differences for the 100 patients were 28 mg/cm2 (2.7%) for Hologic/Norland, 23 mg/cm2 (2.2%) for Hologic/Lunar, and 29 mg/cm2 (2.8%) for Norland/Lunar. Average BMD results for the patients before correction were 0.972 mg/cm2 for Hologic, 1.100 g/cm2 for Lunar, and 0.969 g/cm2 for Norland. After correction, sBMD results for patients were 1045 mg/cm2 for Hologic, 1047 mg/cm2 for Lunar, and 1043 mg/cm2 for Norland. The standardization approach as performed in our study provided compatibility of DXA results obtained on different scanners.