Peak bone mass development of females: can young adult women improve their peak bone mass?

Effects of lifestyle exercise on premenopausal bone health: a randomised controlled trial

Osteoporosis, a slowly evolving public health epidemic, often with an insidious presentation is largely preventable but the optimal dimensions of exercise that may be prescribed for enhancing bone-health among premenopausal adults are yet to be elucidated. Hence, the escalating incidence and burden of prevalence of osteoporosis is yet unabated. Considering that exogenous hormones in the form of hormonal contraception are known to modulate bone mass, investigations of their possible influence on the translation of exercise-induced osteogenic stimuli on the mature bone is pertinent. The aim of this study was to examine the effect of specified lifestyle exercise on bone-health of premenopausal women. Premenopausal women (n = 96, mean age: 22.25 ± 3.5 years; mean BMI: 23.43 ± 3.5 kg/m(2)) participated in a 6-month randomised controlled trial involving home-based rest-interspersed bouts of high-impact exercise for the intervention group and sham exercise for the control group. Approximately half (47) of the participants (24-exercise, 23-control) were on hormonal-based contraception while the other half (49: 24-exercise, 25-control) were not on hormonal contraception. The regime led to a significant 3.7 % increase in broadband ultrasound attenuation of exercisers compared to controls; hormonal contraceptive use did not appear to potentiate the osteogenic effects of the lifestyle exercise regime. The research highlights that short, discrete bouts of high-impact exercise may be a potential public health prescription for enhancing premenopausal bone-health regardless of hormonal contraceptive use.

Bone health and back pain: what do we know and where should we go?

Bone health is generally not considered in patients who present with chronic back pain. Nonetheless, bone health and back pain share common genetic and environmental correlates suggesting a co-dependence. Evidence exists for a relationship between back pain and impaired bone health. Here we present the evidence, theoretic framework and clinical relevance. Bone health and back pain are important determinants of musculoskeletal health. Back pain experienced in youth is a risk factor for future back pain, while suboptimal bone health during development increases the risk of skeletal fragility in later life. Generally, bone health is not considered in patients with chronic back pain who do not demonstrate other well-recognised bone health risk factors or associated conditions. Nonetheless, evidence suggests that back pain and impaired bone health share common environmental and genetic correlates, indicating that bone health ought to be considered in the context of back pain in otherwise healthy individuals. This review describes the likely mechanisms explaining the relationship between back pain and impaired bone health, evidence concerning the relationship and suggestions for future research. A narrative literature search was conducted using CINAHL, Medline, PubMed and Web of Science electronic databases. A history of back pain is associated with decreased bone mineral density in adults, yet this tends to be site-specific. No studies were identified examining this association in youth, yet the negative effects of childhood skeletal trauma and obesity on bone and spinal health provide indirect evidence for an association. Further research is required to clarify the impact of back pain on bone health at different lifespan stages using prospective cohort designs.

Nutritional determinants of bone health

Osteoporosis is a major public health problem. The aging population will require vigilant prevention, education, and treatment to maintain bone density and reduce the risk of fractures and falls. Nutritional requirements of elderly persons can have a profound effect on bone health. Calcium, vitamin D, and protein are vital nutrients for optimal bone health. Adequate calcium is essential for bone maintenance. Vitamin D research shows a link between reduced falls and fractures. Related macro- and micronutrients play an important role in bone mass integrity and quality. Adequate nutrition for older adults needs to be encouraged to promote and maintain bone health.

Milk basic protein increases bone mineral density and improves bone metabolism in healthy young women

Effect of milk basic protein on bone metabolism in healthy young women.

INTRODUCTION

Milk has more beneficial effects on bone health than other food sources. Recent in vitro and in vivo studies have shown that milk whey protein, especially its basic protein fraction (milk basic protein, MBP), contains several components capable of promoting bone formation and inhibiting bone resorption. The object of this study was to examine the effect of MBP on the bone mineral density and bone metabolism of healthy young women.

METHODS

Thirty-five healthy young women were randomly assigned to treatment with either placebo or MBP (40 mg per day) for 6 months. The bone mineral density (BMD) of the lumbar vertebrae L2-L4 of each subject was measured by dual-energy X-ray absorptiometry (DXA) at 0 and 6 months of treatment. Serum and urine indexes of bone metabolism were measured at 0, 3 and 6 months. All subjects completed the study in accordance with the protocol.

RESULTS

The mean rate of gain of lumbar BMD in the MBP group (1.57%) was significantly higher than in the placebo group (0.13%, P=0.042). When compared with the placebo group, urinary cross-linked N-telopeptides of type-I collagen (NTx) were significantly decreased, and serum osteocalcin was significantly increased in the MBP group at 6 months.

CONCLUSION

These results suggested that MBP supplementation was effective in increasing BMD in young women and that this increase in BMD may be primarily mediated through the promotion of bone formation and inhibition of bone resorption by MBP supplementation.

Effects of testosterone on cancellous bone, marrow adipocytes, and ovarian phenotype in a young female rat model of polycystic ovary syndrome

OBJECTIVE

To investigate the effects of testosterone on cancellous bone and marrow adipocytes in a young female rat model of polycystic ovary syndrome (PCOS).

DESIGN

Comparative and controlled study.

SETTING

University animal research laboratory.

PATIENT(S)

Fifty-one Sprague-Dawley rats.

INTERVENTION(S)

The rats were divided into four groups based on the day of testosterone propionate (0.1 mg/weight (g)) injection: no testosterone treatment (control group, C); injected on the ninth day after birth (9D); injected 4 weeks after birth (4W); and injected 8 weeks after birth (8W). About 16 weeks after birth, all animals were killed.

MAIN OUTCOME MEASURE(S)

Bone mineral density (BMD) and bone and fat histomorphometry for the proximal tibia and serum hormonal parameters were measured.

RESULT(S)

The ovaries of group 9D showed many cystic follicles without corpora lutea. The BMD of group 9D (0.309 +/- 0.023 g/cm2) was significantly higher than the other groups groups (CONT, 0.262 +/- 0.017; 4W, 0.256 +/- 0.017; 8W, 0.256 +/- 0.022 g/cm2; P < .0001). Based on bone histomorphometry, group 9D had a higher bone volume (BV/TV), lower bone formation (OV/BV, OS/BS, sLS/BS, MAR, BFR/BS), lower bone resorption (ES/BS, Oc.S/BS), and lower rate of longitudinal growth compared to the other groups. Based on fat histomorphometry, group 9D had a lower bone fat volume and number of fat cells in the bone marrow compared to the other groups. On the other hand, groups 4W and 8W showed similar values of bone and fat histomorphometric parameters to group C.

CONCLUSION(S)

Female rats receiving testosterone within nine days of birth develop polycystic ovaries, high bone volume, low bone turnover, and lower fat content in the bone marrow.

Dietary acid-base balance and intake of bone-related nutrients in Cambridge teenagers

OBJECTIVES

To evaluate the diet of 16-18-y-old boys and girls with particular reference to intakes of nutrients believed to affect bone health and dietary acid-base balance.

DESIGN

A 7-day food diary was completed between the months of October and December.

SETTING

Cambridge, UK.

SUBJECTS

A total of 111 boys and 101 girls aged 16-18 y who were recruited into the Cambridge Bone Studies.

MAIN OUTCOME MEASURES

Mean daily intakes of foods and selected nutrients (protein, calcium, phosphorus, magnesium, potassium, vitamins C and K) were calculated. Two estimates of acid-base balance were calculated from the diet using the formulae of Remer (net acid excretion, estimated indirectly; NAE(ind)) and Frassetto (protein/potassium ratio).

RESULTS

Mean calcium and phosphorus intakes were above the UK Reference Nutrient intake (RNI). In all, 39% of the boys and 36% of the girls had vitamin K intakes lower than 1 microg/kg body weight/day. Calcium intake was positively correlated with all other nutrients except vitamins C and K. Boys had a significantly higher estimated net acid excretion (NAE(ind)) than girls (P<0.001). Although a strong correlation (r=0.76, P<0.001) was found between the two methods, at higher acid levels a divergence was observed. A significant positive correlation was found between NAE(ind) and the weight consumed per day of milk, cheese, meat and cereal foods and a negative correlation was found with the weight of potatoes and fruit. Diet composition is such that a lower NAE(ind) is accompanied by a lower calcium intake.

CONCLUSIONS

The interpretation of the effects of calcium and other nutrients on bone cannot be considered in isolation from the other components of the diet. These results challenge some of the accepted perceptions about what constitutes an optimal diet for the promotion of bone health in adolescents.

High bone mass gained by exercise in growing male mice is increased by subsequent reduced exercise

Exercise-induced bone gains are lost if exercise ceases. Therefore, continued exercise at a reduced frequency or intensity may be required to maintain these benefits. In this study, we evaluated whether 4 wk of reduced exercise after 4 wk of running exercise in growing male mice results in the maintenance of high bone mass. Five-week-old mice were divided into the following groups: 1) baseline control; 2) 4-wk control; 3) 4-wk exercise; 4) 8-wk control; 5) 4-wk exercise followed by 4-wk cessation of training; and 6) 4-wk exercise followed by reduced exercise at half the frequency. The regimen consisted of exercise 6 days/wk, and the reduced exercise regimen consisted of running 3 days/wk on a treadmill for 30 min/day, at 12 m/min on a 10 degrees uphill slope. Running exercise significantly increased bone mineral density of the femur, periosteal mineral apposition rate, bone formation rate, percent labeled perimeter at the midfemur, and osteogenic activity of bone marrow cells. However, these parameters declined to the age-matched sedentary control after cessation of training. In contrast, the reduced exercise group had significantly higher mineral apposition rate compared with those of the sedentary control and cessation of training groups. Furthermore, bone mineral density for the reduced exercise group was significantly higher than those for the other groups. These results suggest that the high bone formation gained through exercise can be maintained, and bone mass was further increased by subsequent exercise even if the exercise frequency is reduced.

RETRACTED: Comparative effects of vitamin K and vitamin D supplementation on prevention of osteopenia in calcium-deficient young rats

This article has been retracted: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy). This article has been retracted at the request of the Editor-in-Chief. The Journal has been made aware of concerns regarding the integrity of the data, authorship and ethical approval for this study. Despite repeated attempts to contact the co-authors we have been unable to confirm the authorship of this paper.

Peak spine and femoral neck bone mass in young women

Achievement of higher peak bone mass early in life may play a critical role against postmenopausal bone loss. Bone mineral density (BMD) of the spine, femoral neck, greater trochanter, Ward's triangle, and spine bone mineral content (BMC) and bone surface area (BSA) were assessed by dual energy x-ray absorptiometry in 300 healthy females (age 6-32 years). Bone measurements were described by using nonlinear models with age, weight, height, or dietary calcium intake as the explanatory variables. At the spine, femoral neck, greater trochanter, and Ward's triangle, the highest BMD level was observed at 23.0 +/- 1.4, 18.5 +/- 1.6, 14.2 +/- 2.0, and 15.8 +/- 2.1 years, respectively. The age of attaining peak spine BMC and BSA cannot be estimated, as significant increases in these two measures were observed through this age group. Age, weight, and height were all significant predictors of all these bone measurements. Weight was a stronger predictor than age for all sites. Dietary calcium intake was not a significant predictor for any of these bone measurements. We conclude that age of attaining peak bone mass at the hip is younger than at the spine, and BMC and BSA at the spine continue to increase through the early thirties in females.

Soy isoflavones: no effects on bone mineral content and bone mineral density in healthy, menstruating young adult women after one year

BACKGROUND

The effects of isoflavone-enriched soy protein on human bone mineral content (mass) and density in healthy, menstruating young adult females have not been examined in a comparative prospective investigation. Peri- and post-menopausal women have been reported to show beneficial effects of isoflavones on bone measurements. Therefore, young women may also be able to improve their accrual of peak bone mineral content (BMC) and bone mineral density (BMD) during the early adult years of bone consolidation with an isoflavone-enriched diet.

OBJECTIVES

In this controlled, double-blind intervention, we tested the hypothesis that an isoflavone-rich soy protein diet increases BMC and BMD in young adult females over a period of one year in comparison to a control group receiving soy protein that has isoflavones removed.

DESIGN

Young healthy women of any ethnic background, 21 to 25 years of age, were divided into two groups, placebo (n = 13) and supplement (n = 15). The soy protein supplement was enriched with isoflavones ( approximately 90 mg of total isoflavones/day), whereas the control protein diet was isoflavone-deficient, even though it contained the same amount of soy protein and other ingredients as the isoflavone-rich diet. Dual-energy x-ray absorptiometric (DXA) measurements of BMC and BMD were made at baseline and at 6 and 12 months. DXA estimates of body composition, including fat mass and lean body mass, were generated from whole-body BMC measurements. BMI was calculated as weight (kg) over height (m) squared. Physical activity was assessed, and three-day dietary records were taken at entry (baseline) and at 6 and 12 months.

RESULTS

No changes in BMD after 12 months were found in either the isoflavone-treated (treatment) group or the isoflavone-deficient (control) group. Other variables also remained essentially constant over the 12-month period, including normal menstrual patterns in both the treatment and control groups.

CONCLUSIONS

The isoflavone-rich soy preparation had no effects on BMC and BMD over a 12-month period in young healthy adult females with normal menses. An isoflavone-rich supplement appears to have little or no effect on bone in young adult women with normal ovarian function, at least over this 12-month study period.

Effect of decreased physical activity on bone mass in exercise-trained young rats

The aim of this study was to determine whether decreased physical activity in exercise-trained young rats would result in a lower rate of bone gain or a reversal of the benefits of exercise. Thirty-five female Wistar rats, 6 weeks of age, were randomized into seven groups: 7 weeks of exercise (7EX), 7 weeks of sedentary control (7CN), 11 weeks of exercise (11EX), 7 weeks of exercise followed by 4 weeks of exercise cessation (7EX4C), 7 weeks of exercise followed by 4 weeks of decreased exercise frequency (7EX4F), 7 weeks of exercise followed by 4 weeks of decreased exercise intensity (7EX4I), and 11 weeks of sedentary control (11CN). The running intensity (speed) and duration were 25 m/min for 60 min/day at a frequency of 5 days/week. During the last 4 weeks, exercise frequency was reduced to 1 day/week in the 11EX4F group, and exercise intensity (speed) was reduced to 12 m/min in the 7EX4I group. After each period of exercise, the bone mineral content (BMC) of the proximal, middle, and distal tibiae, determined by dual-energy X-ray absorptiometry (DXA), was significantly greater in the 7EX and 11EX groups than in the 7CN and 11CN groups, respectively, but it was significantly lower in the 7EX4C group than in the 11EX group and did not differ significantly from the values of the 11CN group. Although the BMC of the proximal and middle tibiae did not differ significantly among the 7EX4F, 7EX4I, 7EX4C, and 11CN groups, the BMC of the distal tibia was significantly greater in the 7EX4F and 7EX4I groups than in the 11CN group and tended to be greater than in the 7EX4C group. The results of this study suggest that the effect of decreased exercise intensity and frequency on bone mass appears to be site specific in the tibia of the exercise-trained young rats. This study shows that exercise-trained young rats lose the benefits gained from exercise when exercise is completely ceased, resulting in the reduction of bone mass to levels that do not differ significantly from those of sedentary controls. At least, continuous exercise appears to be necessary for the maintenance of high bone mass.

Differences in intestinal calcium and phosphate transport between low and high bone density mice

The purpose of this study was to determine whether there are differences in intestinal Ca and phosphate transport in mice having different peak bone densities. Intestinal transport was measured in C57BL/6 (C57, low bone density) and C3H/He (C3H, high bone density) female mice. Unidirectional (mucosal to serosal) transport of Ca was 58% higher in C3H compared with C57 mice, as measured by everted duodenal sacs. The capacity of the duodenal mucosa to take up Ca was also higher in the C3H mice. This uptake highly correlated with Ca transport across the intestine. 1,25-Dihydroxyvitamin D(3) [1,25(OH)(2)D(3)], which stimulates intestinal Ca absorption, markedly stimulated unidirectional Ca transport and uptake to similar levels in both strains of mice. On the other hand, unidirectional phosphate transport in C3H mice was only 36% that of C57 mice. mRNA levels of the plasma membrane Ca pump were 90% higher in the duodenum of C3H mice. There was no difference between strains in duodenal calbindin or 24-hydroxylase mRNA levels. Regarding vitamin D metabolism, there was no difference in serum 1,25(OH)(2)D(3) levels or in renal 1alpha-hydroxylase mRNA levels. The combination of high intestinal Ca transport and low phosphate transport may contribute to the high peak bone density seen in the C3H relative to the C57 mouse.

Risk of irregular menstrual cycles and low peak bone mass during early adulthood associated with age at menarche

BACKGROUND

The risk of irregular menstrual cycles and low peak bone mass of the lumbar spine in young adult women, associated with age at menarche, has not been clearly defined. The aim of this study was to investigate this further.

METHODS

A total of 180 college females aged 20-23 years were surveyed about menstruation, exercise, and calcium intake by means of a questionnaire. We also measured vertebral bone mineral density in these women by dual energy X-ray absorptiometry. The subjects were divided into six groups according to their age at menarche. Comparisons were made of the mean body mass index (BMI) and T-scores (the ratio to the mean bone mineral density of young adult Japanese women) among those groups, and odds ratios of irregular menstrual cycles and low peak bone mass less than 87% (- 1 standard deviation (SD) of T-scores were calculated using the mean menarcheal age (12 years) group as a control.

RESULTS

The mean BMI and T-scores were significantly lower in delayed menarche groups (equal to or more than 13 years) compared with early menarche groups (equal to or less than 12 years). The odds ratios of irregular menstrual cycles were 5.9 (95% confidence intervals (CI) 1.7-20.6), 13.7 (95% CI 3.6-51.6), and 73 (95% CI 6.5-813.9) in the 13-, 14-, and more than 14 years menarcheal age groups, respectively. The odds ratio of low peak bone mass less than 87% (- 1SD) was 3.4 (95% CI 1.1-10.3) in the 14 years menarcheal age group.

CONCLUSIONS

Young adult women with delayed menarche may be at high risk for irregular menstrual cycles and low peak bone mass.

Nutrition in bone health revisited: a story beyond calcium

Osteoporosis is a complex, multi-factorial condition characterized by reduced bone mass and impaired micro-architectural structure, leading to an increased susceptibility to fractures. Although most of the bone strength (including bone mass and quality) is genetically determined, many other factors (nutritional, environmental and life-style) also influence bone. Nutrition is important modifiable factor in the development and maintenance of bone mass and the prevention and treatment of osteoporosis. Approximately 80-90% of bone mineral content is comprised of calcium and phosphorus. Other dietary components, such as protein, magnesium, zinc, copper, iron, fluoride, vitamins D, A, C, and K are required for normal bone metabolism, while other ingested compounds not usually categorized as nutrients (e.g. caffeine, alcohol, phytoestrogens) may also impact bone health. Unraveling the interaction between different factors; nutritional, environmental, life style, and heredity help us to understand the complexity of the development of osteoporosis and subsequent fractures. This paper reviews the role of dietary components on bone health throughout different stages of life. Each nutrient is discussed separately, however the fact that many nutrients are co-dependent and simultaneously interact with genetic and environmental factors should not be neglected. The complexity of the interactions is probably the reason why there are controversial or inconsistent findings regarding the contribution of a single or a group of nutrients in bone health.

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.

Bone mineral density of alveolar bone in rats during pregnancy and lactation

BACKGROUND

The present study was designed to investigate the effect of pregnancy and lactation on the bone mineral density (BMD) of alveolar bone in rats fed diets containing different amounts of calcium (Ca). The effects of different levels of Ca intake by the mothers on the BMD of alveolar bone in their pups were also examined.

METHODS

Ten-week-old female Wistar rats were housed with male rats for breeding and were divided into 3 groups fed diets containing 0.9, 0.3, and 0.02% Ca, respectively. They were further divided into 2 groups according to pregnancy or non-pregnancy. Animals in the pregnant group were raised with their own pups for lactation. After the experiment, all animals were sacrificed, their mandibles were dissected, and soft x-ray microradiographs were taken to determine BMD in the interdental area with an image analyzer.

RESULTS

In both groups, BMD in alveolar bone decreased based on the amount of Ca in the diet, but the magnitude of this decrease was much greater in the pregnant group than in the non-pregnant group. There was no significant difference in BMD between 2 groups fed a 0.9% Ca diet. The BMD of alveolar bone in the pups also decreased depending on the amount of Ca in the diet.

CONCLUSIONS

The above results suggest that pregnancy and subsequent lactation could be risk factors for alveolar bone loss, especially under conditions of Ca insufficiency or deficiency and that Ca insufficiency or deficiency in the mother caused decreases in the BMD of alveolar bone in the pups.

Lactation delays postpartum bone mineral accretion and temporarily alters its regional distribution in women

The objective of this work was to compare long-term changes in bone mineral in lactating (L) and nonlactating (NL) women for 2 y postpartum. The 40 L women (mean duration of breastfeeding 345 +/- 177 d) and 36 NL women were enrolled during late pregnancy. Subjects were healthy and nonsmoking with a mean age of 28.8 +/- 4.1 y. Bone mineral content (BMC) was measured at 0.5, 3, 6, 12, 18 and 24 mo by dual-energy X-ray absorptiometry set for total body scan with regional analysis. BMC adjusted for bone area, weight and height (adj-BMC) decreased in L women at the lumbar spine (-3.1%, P < 0. 001) and pelvis (-0.9%, P = 0.03) by 3 mo, and at the total body (-0. 9%, P = 0.05) by 6 mo. Losses were recovered following onset of menses. Adj-BMC at the lumbar spine, pelvis, thoracic spine and total body increased over baseline by 24 mo in L women. In NL women, adj-BMC increased over baseline within 3 mo and continued to increase thereafter. Net total-body gains were greater in the 27 NL women who completed the final measurement than in their 26 L counterparts (+2.3% vs. +0.6%, P = 0.001). Net regional gains differed at the head, legs, and ribs, but not at the lumber spine, pelvis or thoracic spine. Duration of breastfeeding, parity, onset of menses and maternal age affected bone changes in L women. These results indicate that lactation delays bone mineral accretion and temporarily alters its regional distribution in postpartum women.

Dietary calcium and mineral/vitamin supplementation: a controversial problem

There is a consensus that adequate calcium intake during bone development, and possibly in adulthood and senescence, helps to prevent bone resorption and osteoporosis. The uptake of dietary calcium should be sufficient to maintain both normal serum calcium concentrations and parathyroid hormone levels in the low normal range throughout the day, otherwise, increased bone resorption occurs. Calcium intake varies with race and with environmental and dietary conditions. Estimating the appropriate amount of calcium to be added to dietary sources for an optimal supplementation regimen is therefore difficult. Few intervention studies have evaluated the dose-effect relationship for calcium supplementation conclusively. The mechanisms regulating fractional calcium absorption as a function of intake suggest that very high daily doses are probably useless. They may be unsafe in the long term because of the risks of hypercalciuria and kidney stones, and of an imbalance in the ratio of calcium to magnesium. Concomitant supplementation with limited amounts of magnesium may reduce this risk and improve mineralization. Dietary intake is 500-600 mg/day in most studies, making 400 mg/day an appropriate supplementary dose for most premenopausal women (RDA 1000 mg/day). After the menopause and during lactation (RDA 1200-1500 mg/day), 800 mg/day is probably appropriate, particularly if low doses of vitamin D are taken concomitantly.

Effect of hand dominance on bone mass measurement in sedentary individuals

The aim of this study was to determine in healthy sedentary subjects the effect of hand dominance on side-to-side difference in bone area and bone mass for upper and lower extremities. Dual-energy X-ray absorptiometry (DXA) measurements of both forearms and hips were performed on 193 right-handed and 20 left-handed subjects as determined by self-report. Scan acquisition and scan analyses were performed by one investigator, but all scan pairs were independently assessed for symmetry of positioning and movement artifacts by three investigators. Results show that DXA measurements between sides may be highly correlated regardless of the symmetry of the scan pair. However, asymmetric DXA scan pairs may have more than twice the side-to-side difference found in symmetric DXA scan pairs at the hip. Side-to-side differences between subregions were greater than the differences between measurements at the total radius, ulna, or hip. For symmetric pairs of DXA scans, the dominant forearm has significantly higher bone area and bone mineral content (BMC). Bone mineral density (BMD) was significantly higher only in the ulna of the dominant forearm. However, the nondominant forearm has higher values than dominant forearm in at least one DXA measurement in >24% of the subjects. There were no significant differences in any DXA measurements between hips, and higher DXA measurements did not occur significantly more frequently at the hip corresponding to the dominant hand. We conclude that healthy sedentary subjects tend to have proportionally higher bone area and BMC in the dominant forearm that results in similar BMD between dominant and nondominant forearms. This relationship does not appear to be applicable to measurements at the hip. In addition, there is a significant proportion of subjects with higher bone area and BMC in the nondominant extremities. Thus, in sedentary subjects, the consistency in the use of same extremity and the consistency in scan acquisition techniques and scan analyses is of greater importance than the selection of an extremity based on hand dominance in DXA studies.