Total Body Bone Mass Research Articles

Maternal weight and body composition in the first trimester of pregnancy

Previous studies on weight gain in pregnancy suggested that maternal weight on average increased by 0.5-2.0 kg in the first trimester of pregnancy. This study examined whether mean maternal weight or body composition changes in the first trimester of pregnancy. Prospective observational study. We studied 1,000 Caucasian women booking for antenatal care in the first trimester of pregnancy. Large university teaching hospital. Maternal height and weight were measured digitally in a standardized way and Body Mass Index (BMI) was calculated. Maternal body composition was measured using segmental multifrequency Bioelectrical Impedance Analysis (BIA). Sonographic examination confirmed the gestational age and a normal ongoing singleton pregnancy in all subjects. Maternal weight, maternal body composition. The mean BMI was 25.7 kg/m(2) and 19.0% of the women were in the obese category (> or =30.0 kg/m(2)). Cross-sectional analysis by gestational age showed that there was no change in mean maternal weight, BMI, total body water, fat mass, fat-free mass or bone mass before 14 weeks gestation. Contrary to previous reports, mean maternal weight and mean body composition values remain unchanged in the first trimester of pregnancy. This has implications for guidelines on maternal weight gain during pregnancy. We also recommend that calculation of BMI in pregnancy and gestational weight gain should be based on accurate early pregnancy measurements, and not on self-reported or prepregnancy measurements.

Fat mass and bone development

. Whether a similar association exists in children, implying that fat mass helps the development as well as maintenance of bone, is more controversial. In a cross sectional study, we previously reported that fat mass is positively related to total body bone mass independently of lean mass and height in 3082 boys and girls at a mean age of 9.9 years from the Avon Longitudinal Study of Parents and Children (ALSPAC)

Lean Body Mass, Not Total Body Size, is a Stronger Determinant of Total Body Bone Mass in Boys

Lean Body Mass, Not Total Body Size, is a Stronger Determinant of Total Body Bone Mass in Boys

Peak bone mineral density, lean body mass and fractures

BackgroundDuring childhood and adolescence, bone mass and lean body mass (LBM) increase till a plateau is reached. In this longitudinal and cross-sectional study, the age of reaching the plateau was evaluated for lumbar spine and total body bone mass measurements and lean body mass. The association between fractures and bone mineral density (BMD) was studied. Patients and methodsWe included 501 healthy participants, 141 males and 360 females, aged 13–29 years. Of these 90 had participated in a previous longitudinal study of 444 participants, aged 4–20 years (for the first measurement) and 198 participants, aged 8–25 years (for a second measurement). BMD and body composition were measured with dual energy X-ray absorptiometry (DXA). Volumetric BMD (bone mineral apparent density, BMAD) was calculated. All the data were used to determine the age of reaching the plateau. ResultsThe plateau for lumbar spine BMD, BMAD, total body BMD, bone mineral content and LBM was reached between 18 and 20 years of age in females and between 18 and 23 years in males. The prevalence of fractures was 37% in males and 28% in females. Total body BMD Z-score was significantly lower in all participants who had had a fracture (p<0.05), whereas lumbar spine BMD and BMAD was only significantly lower in females who had had fractures (p=0.007 and p<0.001, respectively). Mean lumbar spine BMAD Z-score at the previous measurement was significantly lower in the participants who had a first fracture between the last two measurements (p=0.04). ConclusionPeak BMD and peak LBM were attained between 18 and 20 years in females and between 18 and 23 years in males in this study using longitudinal and cross sectional data in the age range of 4 to 30 years. A significantly lower total body BMD was seen in participants who had had a fracture and a lower lumbar spine BMD and BMAD in females who had had a fracture. Lumbar spine BMAD Z-score seems to be a good predictor for future fractures.

Osteoprotegerin may be a key determinant of low total body and regional bone mass in obese children

Osteoprotegerin may be a key determinant of low total body and regional bone mass in obese children

Influence of body composition, muscle strength, diet and physical activity on total body and forearm bone mass in Chinese adolescent girls

The aim of the present study was to determine association between body composition, muscle strength, diet and physical exercise with bone mineral content (BMC) and bone area (BA) in 283 Chinese adolescent girls aged 15 years in Beijing, China. Body composition, pubertal stage, physical activity and dietary intakes were assessed using standard validated protocols. Total body and forearm bone, lean body mass (LBM) and fat body mass (FBM) were determined by dual X-ray absorptiometry. Multivariate linear regression analyses were carried out to examine the predictors of BMC and BA, after controlling for potential confounders. The subjects had a mean age of 15.0 (sd 0.9) years and 99.6 % of them had reached menarche. Multivariate analyses showed that LBM, FBM, handgrip muscle strength and milk intake were significant independent determinants of BMC and BA of the total body and/or forearm sites. LBM was found to be a stronger independent determinant than FBM of BMC and BA, whereas handgrip muscle strength was only found as significant determinant of BMC and BA at the forearm sites than in total body BMC and BA. Further, total physical activity level had a significant positive association with handgrip and LBM. This suggested that greater muscle strength and higher LBM may reflect higher levels of physical activity. Therefore, continuous healthy lifestyle practices such as adequate intake of milk and continuous participation in physical activity should be encouraged throughout adolescence to optimise bone growth during this period.

Genetic factors in physical growth and development and their relationship to subsequent health outcomes

Normal physical growth during childhood is influenced by both genetic and environmental factors. However, few studies have examined whether there are shared genetic effects between aspects of child growth and later health outcomes. In this study, we estimate the influence of genetic factors on growth in stature during childhood and determine whether there are pleiotropic effects of genes influencing both childhood growth and later adult health outcomes using familial data. Serial stature data (i.e., birth through adulthood) from participants in the Fels Longitudinal Study were used to derive stature growth parameters. Adult health outcome data for each participant were available for at least one visit after age 30 years. Maximum likelihood-based variance component methods were used to determine the heritability of each parameter and to examine the relationships between growth parameters and adult health outcomes by estimating genetic correlations between the traits. Heritability estimates for the growth parameters are generally high and statistically significant ranging in magnitude from 0.65-0.98. Heritabilities for adult health outcomes are also significant ranging from 0.31-0.98. Results of the phenotypic correlation analysis show that stature growth parameters are significantly related to several adult health outcomes including stature, weight, BMI, systolic and diastolic blood pressure, percent body fat, fat-free mass, skeletal muscle mass in the arms and legs, and total body bone mass. Results of the genetic correlation analysis reveal some evidence of common genetic pathways underlying certain aspects of growth and adult health outcomes including body composition and blood pressure variables.

Dlk1/FA1 Is a Novel Endocrine Regulator of Bone and Fat Mass and Its Serum Level Is Modulated by Growth Hormone

Fat and bone metabolism are two linked processes regulated by several hormonal factors. Fetal antigen 1 (FA1) is the soluble form of dlk1 (delta-like 1), which is a member of the Notch-Delta family. We previously identified FA1 as a negative regulator of bone marrow mesenchymal stem cell differentiation. Here, we studied the effects of circulating FA1 on fat and bone mass in vivo by generating mice expressing high serum levels of FA1 (FA1 mice) using the hydrodynamic-based gene transfer procedure. We found that increased serum FA1 levels led to a significant reduction in total body weight, fat mass, and bone mass in a dose-dependent manner. Reduced bone mass in FA1 mice was associated with the inhibition of mineral apposition rate and bone formation rates by 58 and 72%, respectively. Because FA1 is colocalized with GH in the pituitary gland, we explored the possible modulation of serum FA1 by GH. Serum levels of IGF-I and IGF binding proteins did not change in FA1 mice, whereas increasing serum GH in normal mice using hydrodynamic-based gene transfer procedure dramatically reduced serum FA1 levels by 60%. Conversely, serum FA1 was increased 450% in hypophysectomized mice, and this high level was reduced by 40% during GH treatment. In conclusion, our data identify the FA1 as a novel endocrine factor regulating bone mass and fat mass in vivo, and its serum levels are regulated by GH. FA1 thus provides a novel class of developmental molecules that regulate physiological functions of the postnatal organisms.

Effects of Exercise During Diet-Induced Weight Loss on Bone Mineral Density in Obese Middle-Aged Men

Diet-induced weight loss may result in bone mass reduction. Information on this issue in men is scarce as most researchers have focused on women. PURPOSE: To compare the effect of exercise during diet-induced weight loss on bone mineral density and body composition in men. METHODS: Forty-four obese (Japanese criterion: BMI >25 kg/m2) men (age 50.1 ± 10.5 years, weight 79.0 ± 6.2 kg, and BMI 27.8 ± 1.7 kg/m2) were randomly assigned to either a diet (D; n = 22) or diet plus aerobic exercise (DA; n = 22) group. They were instructed to restrict energy intake to 1680 kcal/d. Group DA completed 3 exercise sessions per week consisting of brisk walking and mild jogging. Total-body bone mineral density (BMD), bone mineral content (BMC), fat mass (FM), lean mass (LM), percentage of fat (%fat), and regional BMD (femoral neck, lumbar spine, and radius) were measured by dual energy X-ray absorptiometry before and after 14-week intervention periods. Statistical significance was set at P < 0.05. RESULTS: During these interventions, body weight decreased significantly in groups D (−7.4 ± 3.4 kg) and DA (−8.6 ± 3.0 kg). Total-body BMD, BMC, FM, and %fat, as well as ultra-radius BMD and 33% radius BMD, also decreased significantly in both groups. Total-body LM and total proximal-femur BMD was significantly reduced only in Group D, whereas BMD in Ward's area and lumbar spine increased significantly. Two-way analysis of variance revealed a significant interaction (time by intervention) in total-body BMC and total proximal-femur BMD. CONCLUSIONS: These results suggest that aerobic exercise could prevent regional BMD reduction (especially in loading regions), but total-body bone mass may not be maintained during weight loss.

Calcium supplementation during pregnancy and lactation: Effects on the mother and the fetus

Calcium consumption is essential for bone development and maintenance throughout life, yet more than one half of the female population in the United States does not consume the recommended amount of calcium. Calcium intake is especially crucial during pregnancy and lactation because of the potential adverse effect on maternal bone health if maternal calcium stores are depleted. There is often a transient lowered bone mineral density and increased rate of bone resorption, with the greatest consequence during the third trimester and throughout lactation. Studies indicate that calcium consumption should be encouraged, especially during pregnancy and lactation, to replace maternal skeletal calcium stores that are depleted during these periods. Because the fetus in utero and the neonate through breast-feeding are dependent on maternal sources for the total calcium load, adequate maternal calcium intake also can affect fetal bone health positively. Proper calcium consumption can be attained through the diet by the consumption of dairy products or leafy greens (such as kale), the consumption of fortified foods, or by supplementation with widely available calcium-containing supplement products. Because many women experience heartburn during pregnancy, calcium-based antacids are ideal for providing heartburn relief, and they offer a calcium supplement to ensure maternal and fetal bone health, without the danger of adverse effects on the neonate.

Bone Response to Intermittent Parathyroid Hormone Is Altered in Mice Null for β-Arrestin2

Intermittent PTH administration increases bone turnover, resulting in net anabolic effects on bone. These effects are primarily mediated by intracellular cAMP signaling. However, the molecular mechanisms that regulate PTH activity in bone remain incompletely understood. beta-Arrestin2, a G protein-coupled receptor regulatory protein, inhibits PTH-stimulated cAMP accumulation in vitro. Using beta-arrestin2(-/-) (KO) and wild-type (WT) mice, we investigated the response to PTH in primary osteoblasts (POB) and the effects of intermittent PTH administration on bone mass and microarchitecture in vivo. Compared with that in WT mice, PTH-stimulated intracellular cAMP was increased and sustained in KO POB. Intermittent exposure of POB to PTH significantly decreased the ratio of osteoprotegerin (OPG) receptor activator of nuclear factor-kappaB ligand (RANKL) mRNA expression in KO POB, whereas it increased this ratio in WT POB. Total body bone mass and cortical and trabecular bone parameters were 5-10% lower in male KO mice compared with WT, and these differences were magnified upon in vivo administration of intermittent PTH (80 mug/kg.d) for 1 month. Thus, PTH significantly increased total body bone mineral content as well as vertebral trabecular bone volume and thickness in WT, but not KO mice. The anabolic response to PTH in cortical bone was also slightly more pronounced in WT than KO mice. Histomorphometry indicated that PTH prominently stimulated indexes of bone formation in both WT and KO mice, whereas it significantly increased indexes of bone resorption (i.e. osteoclast number and surface) in KO mice only. In conclusion, these results suggest that beta-arrestins may specify the activity of intermittent PTH on the skeleton by limiting PTH-induced osteoclastogenesis.

Bone mass in Chinese premenarcheal girls: the roles of body composition, calcium intake and physical activity

The association of growth and anthropometric characteristics and lifestyle factors with bone mass and second metacarpal radiogrammetry parameters was evaluated in 373 healthy Chinese premenarcheal girls aged 9-11 years. Bone mineral content (BMC) and density (BMD) and bone area (BA) of distal forearm, proximal forearm and total body, bone mineral-free lean (BMFL) mass and fat mass were measured by dual-energy X-ray absorptiometry. Metacarpal bone periosteal and medullary diameters were measured. Dietary intakes were assessed by 7 d food record and physical activity (PA) by questionnaire. BMFL and fat mass together explained 6.3 and 51.6% of the variation in total body BMC and BMD, respectively. BMFL mass contributed to a substantial proportion of the variation in forearm BMC and BMD and periosteal diameter (10.4-41.0%). The corresponding BA explained 14.8-80.4% of the variation in BMC. Other minor but significant predictors of total body bone mass were Ca intake, height, age and PA score (BMD only), and of forearm bone mass were PA score, bone age, height and fat mass. Nevertheless, after adjusting for bone and body size and for age or bone age, subjects with Ca intake above the median (417 mg/d) had 1.8% greater total body BMC (P<0.001), and subjects with PA scores above the median had 2.4-2.5% greater distal and proximal forearm BMC (P<0.05) than those below. Vitamin D intake negatively associated with medullary diameter (partial R2 1.7%). The results indicate that premenarcheal girls should be encouraged to optimise nutrition and Ca intake and exercise regularly to achieve maximum peak bone mass.

The skeletal phenotype of men with previous constitutional delay of puberty.

It is presently unclear whether men with a history of constitutional delay (CD) of puberty are osteopenic. This study compares auxology, bone mass, size, and density of 32 men (age, 21-33 yr) with previous CD with 45 controls. Using dual-energy x-ray absorptiometry, areal bone mineral density (aBMD) and volumetric bone mineral density at the lumbar spine (LS) and femoral neck (FN), hip strength analysis, and total-body and body segment (arms, legs, trunk) measurements were determined. Auxological variables, body composition, the muscle-bone relation, and the effect of prior androgen treatment were studied. Men with previous CD were shorter (P < 0.001) and had shorter height-adjusted arms compared with controls. Height-adjusted total-body bone mineral content (BMC) (P = 0.004), aBMD (P = 0.016), and bone area (P = 0.006) but not lean tissue mass (P = 0.507) were lower in CD men compared with controls; consequently, their BMC to lean tissue mass ratio was reduced (P < 0.001). Segment length-adjusted BMC and bone area of arms (P < 0.001) and legs (P < 0.03), but not trunk were lower in CD men than in controls. They had lower LS aBMD (P = 0.044) but normal LS and FN volumetric bone mineral density. Size-adjusted LS width and the hip cross-sectional area were lower than in controls. There was no difference in anthropometric or dual-energy x-ray absorptiometry results between untreated (n = 15) and androgen-treated (n = 17) CD men.We conclude that men with previous CD have normal LS and FN volumetric density but reduced total-body bone mass, which was explained by reduced limb bone mass and size. Together with the reduced LS bone width and hip crosssectional area, these skeletal characteristics suggest impaired periosteal expansion during puberty. The skeletal phenotype of CD males may be altered by their late onset of puberty.

Prediction models for evaluation of total-body bone mass with dual-energy X-ray absorptiometry among children and adolescents.

The performance of dual-energy x-ray absorptiometry (DXA) in identifying children with decreased bone mass is increasing, but there is no consensus regarding how to interpret the results. The World Health Organization diagnostic categories for normal, osteopenia, and osteoporosis, based on T scores, are not applicable to children and adolescents who have not yet reached peak bone mass. The pediatric reference standards provided by DXA manufacturers have been questioned. Bone mineral density determined with DXA is "areal" density (a 2-dimensional measurement of a 3-dimensional structure), and its misleading nature among growing and maturing children is well recognized. Few published pediatric reference values for bone mineral density measured with DXA include factors that are known to affect the results besides age and gender. Our objective was to develop an algorithm for the evaluation of bone mass among children that included known determinants of bone mass and of its measurement with DXA. Height, weight, pubertal status, and total-body bone mineral content, total-body bone area, and total-body bone mineral density measured with DXA were recorded for an ethnically diverse group of healthy pediatric subjects (n = 1218; age: 6-18 years). Prediction models for bone measurements were developed and validated with healthy pediatric subjects and then applied to children with medical disorders. There was a significant gender effect, as well as an interaction between gender and ethnicity. Separate models were developed for log total-body bone mineral content, log total-body bone area, and 1/total-body bone mineral density for girls and boys. The variability explained for each measurement increased from level 1, including age and ethnicity (76-86%), to level 2, including age, ethnicity, height, and weight (84-97%), and to level 3, including age, ethnicity, height, weight, and bone area (89-99%). Pubertal stage was an additional significant predictor of bone measurements but increased the explained variability by only 0.1% with height and weight in the models. The values predicted with each model were not different from measured values for the validation group but were different for patients with medical disorders, with different patterns according to the diagnoses. These models, including known determinants of bone mass and of bone measurements with DXA, provide an evaluation of pediatric bone mass that proceeds in steps from level 1 to level 3. The outcomes were different for patients at risk for compromised bone mass, compared with healthy children, with specific patterns for each medical disorder. We propose an algorithm for evaluation of bone measurements that follows levels 1 to 3. Our findings suggest that application of this algorithm to well-characterized groups of pediatric patients could identify disease-specific features of DXA results. We recommend this approach as a basis for consensus regarding the clinical evaluation of pediatric bone mass, and we suggest that it could lead to meaningful classification of pediatric bone disorders, investigation of pathophysiologic processes, and development of appropriate interventions.

The association between hormone therapy use and changes in strength and body composition in early postmenopausal women.

To prospectively examine potential differences in upper- and lower-body muscle strength, lower-body power, lean muscle mass, total body fat, intra-abdominal fat, and energy expenditure (METS) variables in early postmenopausal women. Measurements were taken at baseline and 12 months. Prospective, 1-year non-randomized [self-selected hormone therapy (HT) and non-HT-replaced], longitudinal study with participation from 136 normally active, early [14.2 +/- 9.8 mo past menopause (51.1 +/- 3.0 y) mean age +/- SD] postmenopausal women. Total body fat mass, lean mass, and bone mass were assessed by dual-energy x-ray absorptiometry (Hologic), METS (6-mo activity recall questionnaire) upper- and lower-body peak force by isokinetic dynamometry (KinCom 500H, Chattex Corp.), and leg power by the Bassey Power Rig (Nottingham, UK). We observed no significant differences in central adipose tissue, total fat mass, lean muscle mass, strength, or lower limb power. However, estrogen did promote a maintenance affect in bone mineral density at the spine and total hip and an increase in greater trochanter bone mineral density (P < 0.01) in the estrogen-replaced group. Our findings suggest that HT does not play a role in either increasing or maintaining strength, lean muscle mass, lower limb power, or the attenuation of increases in total body or abdominal fat, at least in this group of postmenopausal women during the initial years of menopause

Visceral fat is more important than peripheral fat for endometrial thickness and bone mass in healthy postmenopausal women

Objective: The purpose of this study was to investigate the influence of body mass index and body composition on endometrial thickness and bone mass. Study design: This was a cross-sectional study that included 531 healthy postmenopausal women aged 48 to 65 years. Endometrial thickness was measured as double-layer thickness. Body composition was measured by dual energy x-ray absorptiometry, which divides the body into fat mass, lean mass, and bone mass, both for the total body and regional body compartments. An abdominal region was inserted manually. Statistics were Pearson correlations and analysis of variance. Results: Endometrial thickness and total body bone mass were correlated, respectively, to body mass index (r = 0.14, P < .01; r = 0.35, P < .001), total body fat mass (r = 0.14, P < .01; r = 0.38, P < .001), abdominal fat mass (r = 0.16, P < .001; r = 0.33, P < .001), peripheral fat mass (r = 0.10, P < .05; r = 0.41, P < .001), and abdominal/peripheral fat mass (r = 0.12, P < .01; r = 0.11, P < .01). Conclusion: High body mass index and abdominal fat distribution correlate with increased endometrial thickness and bone mass. (Am J Obstet Gynecol 2003;188:349-53.)

A potent analog of 1alpha,25-dihydroxyvitamin D3 selectively induces bone formation.

1,25-Dihydroxyvitamin D(3) [1,25(OH)(2)D(3)] is a principal regulator of calcium and phosphorus homeostasis through actions on intestine, kidney, and bone. 1,25(OH)(2)D(3) is not considered to play a significant role in bone formation, except for its role in supporting mineralization. We report here on the properties of 2-methylene-19-nor-(20S)-1alpha,25(OH)(2)D(3) (2MD), a highly potent analog of 1,25(OH)(2)D(3) that induces bone formation both in vitro and in vivo. Selectivity for bone was first demonstrated through the observation that 2MD is at least 30-fold more effective than 1,25(OH)(2)D(3) in stimulating osteoblast-mediated bone calcium mobilization while being only slightly more potent in supporting intestinal calcium transport. 2MD is also highly potent in promoting osteoblast-mediated osteoclast formation in vitro, a process essential to both bone resorption and formation. Most significantly, 2MD at concentrations as low as 10(-12) M causes primary cultures of osteoblasts to produce bone in vitro. This effect is not found with 1,25(OH)(2)D(3) even at 10(-8) M, suggesting that 2MD might be osteogenic in vivo. Indeed, 2MD (7 pmol/day) causes a substantial increase (9%) in total body bone mass in ovariectomized rats over a 23-week period. 1,25(OH)(2)D(3) (500 pmol three times a week) only prevented the bone loss associated with ovariectomy and did not increase bone mass. These results indicate that 2MD is a potent bone-selective analog of 1,25(OH)(2)D(3) potentially effective in treating bone loss diseases.

Short-term Administration of Glucagon-like Peptide-2. Effects on Bone Mineral Density and Markers of Bone Turnover in Short-Bowel Patients with No Colon

Background: Glucagon-like peptide 2 (GLP-2) is a newly discovered intestinotrophic hormone. We have recently reported that a 5-week GLP-2 treatment improved the intestinal absorptive capacity of shortbowel patients with no colon. Additionally, GLP-2 treatment was associated with changes in body composition that included a significant increase in total body bone mass. This article describes the effect of GLP-2 on spinal and hip bone mineral density (BMD) and biochemical markers of bone turnover in these patients. Methods: In an open-labelled pilot study, eight short-bowel patients (3M, 5F; mean age 49 years) with small-bowel resection and no colon received 400 μg s.c. of GLP-2 twice daily for 5 weeks. Four received home parenteral nutrition (mean length of residual jejunum 83 cm) and 4 did not (mean length of ileum resected 106 cm). The outcome measures were the mean percent change from baseline in spinal and hip BMD measured by dual-energy X-ray absorptiometry, changes in four biochemical markers of bone-turnover, PTH, 25-hydroxy vitamin-D, and the intestinal absorption of calcium. Results: Mean ± s x (SEM) percent changes in spinal and hip BMD were 1.1 ± 0.4% ( P < 0.05) and 1.9 ± 0.8% ( P = 0.06), respectively. The intestinal calcium absorption increased by 2.7% ( P = 0.87). Serum ionized calcium increased in 5/8 patients with a concomitant decrease in serum PTH values. Three of the four markers of bone turnover decreased. Conclusion: A 5-week GLP-2 administration significantly increased spinal BMD in short-bowel patients with no colon. The mechanism by which GLP-2 affects bone metabolism remains unclear, but may be related to an increased mineralization of bone resulting from an improved intestinal calcium absorption.

Skeletal sensitivity to dietary calcium deficiency is increased in the female compared with the male rat

We investigated potential sex differences in bone resorption and the conservation of whole body bone mass in 24-week-old Sprague-Dawley rats maintained on a 1.0% calcium diet and then fed diets containing 0.02, 0.5, 1.0, or 1.75% calcium for 31 days. Lowering dietary calcium from 1.00% to 0.02% doubled whole skeleton bone resorption (urinary 3H-tetracycline loss). Female rats were more sensitive to calcium stress, exhibiting the maximal resorptive response when fed the 0.5% calcium diet, whereas the 0.02% calcium diet was required to elicit this response in males. Despite the evidence of increased bone resorption, whole skeleton mass was unchanged in females and was significantly increased in males, indicating that switching to even the 0.02% calcium diet did not result in an overt loss of total body bone mass. Compared with controls, the skeleton mass of females (97 ± 1.4%) maintained on the 0.02% calcium diet was significantly lower than males (107 ± 2.4%), again suggesting a greater impact of calcium deficiency in females. The calculation of the average percentage growth of selected individual bones in male rats indicated a proportional increase in bone mass between the axial and appendicular skeleton of approximately +4% and +18% in animals maintained on 0.02 and 1.75% diets, respectively. By comparison, female rats consuming the 0.02% calcium diet showed an average 14% loss in axial bone and 7.5% gain in appendicular bone mass. The results indicate increased sensitivity to dietary calcium deficiency in female rats which involves a significant loss in axial bone mass not observed in male rats maintained under similar dietary conditions.Key words: skeleton bone mass, calcium diet, 3H-tetracycline, axial, appendicular, gender, sex.

Skeletal sensitivity to dietary calcium deficiency is increased in the female compared with the male rat

We investigated potential sex differences in bone resorption and the conservation of whole body bone mass in 24-week-old Sprague-Dawley rats maintained on a 1.0% calcium diet and then fed diets containing 0.02, 0.5, 1.0, or 1.75% calcium for 31 days. Lowering dietary calcium from 1.00% to 0.02% doubled whole skeleton bone resorption (urinary 3H-tetracycline loss). Female rats were more sensitive to calcium stress, exhibiting the maximal resorptive response when fed the 0.5% calcium diet, whereas the 0.02% calcium diet was required to elicit this response in males. Despite the evidence of increased bone resorption, whole skeleton mass was unchanged in females and was significantly increased in males, indicating that switching to even the 0.02% calcium diet did not result in an overt loss of total body bone mass. Compared with controls, the skeleton mass of females (97+/-1.4%) maintained on the 0.02% calcium diet was significantly lower than males (107+/-2.4%), again suggesting a greater impact of calcium deficiency in females. The calculation of the average percentage growth of selected individual bones in male rats indicated a proportional increase in bone mass between the axial and appendicular skeleton of approximately +4% and +18% in animals maintained on 0.02 and 1.75% diets, respectively. By comparison, female rats consuming the 0.02% calcium diet showed an average 14% loss in axial bone and 7.5% gain in appendicular bone mass. The results indicate increased sensitivity to dietary calcium deficiency in female rats which involves a significant loss in axial bone mass not observed in male rats maintained under similar dietary conditions.