Overweight and obese children have low bone mass and area for their weight

Postural control in obese adolescents assessed by limits of stability and gait initiation

The biomechanical changes in postural control and in motor activities linked to obesity are still not fully understood. The aim of this study was to assess the adaptation in static and dynamic control of equilibrium when the body mass to be stabilized and moved is increased through obesity. Postural stability limits and gait initiation at slow and fast velocities were compared in a case control study that included a group of obese adolescents and a control group of adolescents with normal weight. The consequences of overweight are more clearly evident from the results on dynamic stability of the obese group than those on static equilibrium. Both the lower values of the biomechanical parameters characterizing the progression velocity of gait and the longer duration of the swing phase for the fast velocity condition suggest that obesity acts as a slowing factor. However, the reduction of the postural stability limits of the obese group, their inability to increase the anticipatory phase duration unlike the control group, the increase in the double support phase duration as well as some difficulty in controlling the fall of the centre of gravity suggest that, in these subjects, an adaptive strategy is adopted to preserve equilibrium by limiting progression velocity.

Evaluation of bone mass in children with long bone fracture compared with controls

Childhood is a critical period for achieving skeletal mass. In adults, low bone density is associated with an increased fracture risk and it has been postulated that the same is true for children. If this were the case, we would expect that children with fractures might have a lower bone mass than those without. A case-control study of 30 cases and 30 age and sex-matched controls was carried out. Each child underwent height and weight measurements, a simple interview and phalangeal ultrasound to measure speed of sound. The difference in mean speed of sound was -51.81 m/s (95% confidence interval -83.0 to -20.6; P=0.002) in children with simple long bone fractures versus controls. In children, there appears to be a significant difference in bone mass between those with a simple long bone fracture and those who have never sustained a fracture. To be certain that this is owing to cause rather than effect, and also as this is an important public health issue, further studies are warranted.

Body composition and bone density in Canadian White and Aboriginal women: the First Nations Bone Health Study

Ethnic variation in soft tissue composition may contribute to observed ethnic differences in bone mineral density (BMD). This analysis was performed to determine whether ethnic differences in body composition affect differences in BMD between Canadian White and Aboriginal women. An age-stratified population-based sample of 206 Aboriginal women and 177 White women underwent multisite bone density measurements and total body soft tissue composition analysis. In univariate analyses, each kg of additional lean mass was associated with a greater increase in BMD than an equal amount of fat mass (p<.01). When models simultaneously evaluated both soft tissue measurements, lean mass (but not fat mass) was positively correlated with BMD at all measurement sites (p<.001). Aboriginal women had significantly lower weight-adjusted BMD than White women for two sites (calcaneus, p = .019; total body, p = .026) and lower BMI-adjusted for BMD three sites (calcaneus, p = .0076; distal forearm, p = .047; total body, p = .022). The ratio of lean mass to fat mass was lower in Aboriginal than White women (p<.001). When BMD was adjusted for body composition variables no significant difference was seen between Aboriginal and White women. Apparent ethnic differences in weight- and BMI-adjusted BMD between Canadian White and Aboriginal women were explained by a lower ratio of lean mass to fat mass in Aboriginal women, combined with a smaller increment in BMD from fat mass versus lean mass in both populations.

Relationships between fat and bone

Body weight impacts both bone turnover and bone density, making it, therefore, an important risk factor for vertebral and hip fractures and ranking it alongside age in importance. The effect of body weight is probably contributed to by both fat mass and lean mass, though in postmenopausal women, fat mass has been more consistently demonstrated to be important. A number of mechanisms for the fat-bone relationship exist and include the effect of soft tissue mass on skeletal loading, the association of fat mass with the secretion of bone active hormones from the pancreatic beta cell (including insulin, amylin, and preptin), and the secretion of bone active hormones (e.g., estrogens and leptin) from the adipocyte. These factors alone probably do not fully explain the observed clinical associations, and study of the actions on bone of novel hormones related to nutrition is an important area of further research. An understanding of this aspect of bone biology may open the way for new treatments of osteoporosis. More immediately, the role of weight maintenance in the prevention of osteoporosis is an important public health message that needs to be more widely appreciated.

Relationship of total body fat mass to bone area in New Zealand five-year-olds

Fat mass was recently shown to be a positive determinant of bone mass and size independently of lean mass in a birth cohort of British 9-year-olds. The present study was undertaken to investigate whether similar relationships are evident in younger, preschool children. Height and weight were measured, and a total-body dual-energy X-ray absorptiometric scan was performed on 194 preschool New Zealand children (81 girls, 113 boys) participating in the Dunedin birth cohort Family, Lifestyle, Activity, Movement, and Eating (FLAME) study close to their fifth birthday. Relationships of total-body fat mass and lean mass to total-body-less-head (TBLH) bone area and TBLH bone mineral content (BMC) were evaluated using linear regression. Girls had higher mean fat mass (3.9 vs. 3.2 kg) and lower lean mass (14.5 vs. 15.2 kg) than boys (P < 0.001), but their heights, weights, and TBLH bone area were similar. Although a given weight of lean tissue was associated with greater increases in TBLH area than a given weight of fat tissue, our results show that fat mass was an independent predictor of TBLH bone area (R (2 )= 0.79, P < 0.001) and TBLH BMC (R (2) = 0.74, P < 0.001) in data adjusted for socioeconomic status, ethnic group, lean mass, and height. We conclude that increased fat mass is associated with outward expansion of the TBLH skeletal envelope (wider bones) independently of height and lean mass in very young children.

Proximal femur mechanical adaptation to weight gain in late adolescence: a six-year longitudinal study

The effect of weight gain in late adolescence on bone is not clear. Young women who consistently gained weight (n = 23) from 17 to 22 yr of age had increased BMD but a lack of subperiosteal expansion compared with stable weight peers (n = 48). Bone strength increased appropriately for lean mass in both groups but decreased relative to body weight in weight gainers, suggesting increased bone fragility in weight gainers.

INTRODUCTION

Weight gain leading to obesity often starts in adolescence, yet little is known about its effects on bone. We used longitudinal data to examine the effects of weight gain in late adolescence (from 17 to 22 yr of age) on proximal femur BMD, geometry, and estimates of bending strength.

MATERIALS AND METHODS

Participants were classified as either weight gainers (WG, n = 23) or stable weight (SW, n = 48) using a random coefficients model. Weight gainers had positive increases in weight (p < 0.05) at each clinic visit from age 17 onward. Proximal femur DXA scans (Hologic QDR 2000) taken annually from 17 to 22 yr of age were analyzed for areal BMD (g/cm(2)), subperiosteal width (cm), and bone cross-sectional area (CSA) at the proximal femoral shaft. Cortical thickness was measured, and section modulus (Z, cm(3)) was calculated as a measure of bone bending strength. Total body lean (g) and fat (g) mass were measured from DXA total body scans.

RESULTS

Over ages 17-22, height remained stable in both groups. Weight remained static in the SW group but increased 14% on average in the WG group (p < 0.05). After controlling for age 17 baseline values, WG had higher BMD (+2.6%), thicker cortices (+3.6%), and greater bone CSA (+2.3%). Increased BMD did not translate to greater increases in bone bending strength (Z). The SW group achieved similar gains in Z by greater subperiosteal expansion. Bone strength index (SI = Z/height) normalized for body weight remained constant in the SW group but decreased significantly in the WG group. In contrast, SI normalized to lean mass did not change over time in either group. Other variables including physical activity, nutrition, and hormone levels (estradiol, testosterone, cortisol) did not differ significantly between groups.

CONCLUSIONS

These data suggest that weight gain in late adolescence may inhibit the periosteal expansion known to normally occur throughout life in long bones, resulting in decreased bone strength relative to body weight.

Bone mineral density in prepubertal obese and control children: relation to body weight, lean mass, and fat mass

The aim of the study was to determine the influence of obesity on bone status in prepubertal children. This study included 20 obese prepubertal children (10.7 +/- 1.2 years old) and 23 maturation-matched controls (10.9 +/- 1.1 years old). Bone mineral area, bone mineral content (BMC), bone mineral density (BMD), and calculation of bone mineral apparent density (BMAD) at the whole body and lumbar spine (L1-L4) and body composition (lean mass and fat mass) were assessed by DXA. Broadband ultrasound attenuation (BUA) and speed of sound (SOS) at the calcaneus were measured with a BUA imaging device. Expressed as crude values, DXA measurements of BMD at all bone sites and BUA (69.30 versus 59.63 dB/MHz, P < 0.01) were higher in obese children. After adjustment for body weight and lean mass, obese children displayed lower values of whole-body BMD (0.88 versus 0.96 g/cm2, P < 0.05) and BMC (1190.98 versus 1510.24 g, P < 0.01) in comparison to controls. When results were adjusted for fat mass, there was no statistical difference between obese and control children for DXA and ultrasound results. Moreover, whole-body BMAD was lower (0.086 versus 0.099 g/cm3, P < 0.0001), whereas lumbar spine BMAD was greater (0.117 versus 0.100 g/cm3, P < 0.001) in obese children. Thus, it was observed that, in obese children, cortical and trabecular bone displayed different adaptation patterns to their higher body weight. Cortical bone seems to enhance both size and BMC and trabecular bone to enhance BMC. Finally, considering total body weight and lean mass of obese children, these skeletal responses were not sufficient to compensate for the excess load on the whole body.

Observational study of bone accretion during successful weight loss in obese adolescents

OBJECTIVE

To assess bone mineral content (BMC) among obese adolescents who lose weight during a critical period for bone accretion.

METHODS AND PROCEDURES

Whole body, lumbar spine, lower, and upper limb BMC were measured in 62 obese adolescents who completed an intensive 12-month weight loss trial. BMC was adjusted for height (z -scores) using data from a reference group of 66 adolescents (who were 18% overweight).

RESULTS

At baseline, the BMC of the obese group was higher than the reference group. During the 12-month weight loss program, unadjusted BMC increased among the obese adolescents, despite successful weight loss. After adjustment for height, whole body BMC did not change significantly from baseline to 12 months (mean +/- s.d.: 1.08 +/- 0.67 to 1.06 +/- 0.67, P = 0.7). Region-specific BMC-for-height however decreased for the lower (1.07 +/- 0.57 to 0.95 +/- 0.59, P < 0.001) and upper (1.29 +/- 0.56 to 1.18 +/- 0.57, P = 0.01) limbs, but lumbar spine BMC-for-height increased (0.14 +/- 1.06 to 0.40 +/- 0.94, P < 0.001). These changes were largely and independently explained by changes in lean and fat mass.

DISCUSSION

This study confirms that obese adolescents have high BMC for height and suggests that, unlike adults, their BMC continues to increase during weight loss and remains higher than the BMC of a reference group. After adjustment for growth-related changes, lower and upper limb BMC appears to decrease, while lumbar spine BMC appears to increase. These results suggest that to optimize the health benefits of weight loss among obese adolescents, their bone health should be better understood and addressed.

Is adiposity advantageous for bone strength? A peripheral quantitative computed tomography study in late adolescent females

BACKGROUND

Whereas excess adiposity is presumed to be advantageous for the skeleton, studies investigating relations between bone strength and fat during youth have been equivocal.

OBJECTIVES

Relations of percentage body fat (BF) and bone strength indexes were assessed in late adolescent females, taking into consideration surrogates of muscle force [ie, muscle cross-sectional area (MCSA) and bone length]. Bone measurements in the normal- and high-fat groups were also compared.

DESIGN

Late adolescent females (n = 115; aged 18.2 +/- 0.4 y) participated in this cross-sectional study. Fat-free soft tissue mass, fat mass, and percentage BF were measured with the use of dual-energy X-ray absorptiometry. Tibial and radial peripheral quantitative computed tomography measurements were taken at the 4% (trabecular bone), 20% (cortical bone), and 66% (for measurement of MCSA) sites from the distal metaphyses.

RESULTS

Percentage BF was inversely related to radial cortical bone area, total bone cross-sectional area (CSA), cortical bone mineral content (BMC), periosteal circumference, and strength-strain index (SSI) (20% site; all P < 0.05). After control for MCSA and limb length, negative relations remained between percentage BF and radial measurements and were also observed at the tibia (20% site). Unadjusted bone measures were not different between groups. After control for MCSA, the high- compared with the normal-fat group had lower bone measures at the 20% site (cortical bone area and cortical BMC at the tibia, total bone CSA at the radius, and SSI at both the tibia and radius; P < 0.05 for all).

CONCLUSION

Excess weight in the form of fat mass does not provide additional benefits, and may potentially be negative, for adolescent bone.

Anthropometric, bone age, and bone mineral density changes after a family-based treatment for obese children

Our objective was to identify anthropometric, bone age, and bone mineral density (BMD) changes after a family-based treatment program for obese children. We conducted a longitudinal prospective study of 50 obese children (body mass index percentage [BMI%] > or =120%) aged 9.12 +/- 1.72 years (range 6-13) at baseline. A family-based treatment program, based on inadequate feeding style with progressive modification, aerobic physical exercise increase, active parental involvement, and the use of behavioural strategies (contracting, self-monitoring, social reinforcement), was developed during a 12-month period. Anthropometric data, lumbar spine (L2-L4) BMD by dual-energy X-ray absorptiometry, bone age (BA), bone age to chronological age ratio (BA/CA), and predicted adult height (PAH) were determined at baseline and 12 months. The statistical method used was analysis of variance and the paired Student t-test. Mean BMI standard deviation score (SDS) loss was -0.61 +/- 0.76 and BMI% loss was -5.17 +/- 9.73%. Height SDS significantly decreased, BA/CA ratio also decreased significantly, and PAH change was not significant. Lumbar spine BMD SDS and BMD% did not significantly change. A family-based treatment program was effective in obese children by reducing by 5% the BMI in 1 year and increasing the activity level. Treatment reduced growth velocity and delayed bone maturation rate without affecting PAH, reflecting a situation of previous early maturation. The treatment did not modify gaining bone mass.

Picking a bone with contemporary osteoporosis management: Nutrient strategies to enhance skeletal integrity

Epidemic rates of osteoporosis in the western world have yielded intense efforts to develop management approaches to combat this potentially devastating disorder; recent research has unveiled innovative strategies which hold considerable promise for prevention of skeletal compromise and amelioration of suboptimal bone health. According to many algorithms and practice directives, the contemporary assessment and management of osteoporosis focuses heavily on determination of fracture risk and pharmaceutical intervention for those patients deemed to be at high risk. While routine recommendations for calcium and vitamin D have been incorporated into most regimens, disproportionately little attention has been given to recent research elucidating improved bone health and diminution in fracture rates experienced by patients receiving specific nutrients. In mainstream medical practice, clinical analysis and management of nutritional or dietary issues is sometimes perceived as unconventional, primitive or unsophisticated health care. Recent evidence-based research, however, supports intervention with adequate amounts of specific nutrients including vitamin D, strontium, vitamin K, and essential fatty acids in the prevention and primary management of osteoporosis.

Glucocorticoid-induced osteoporosis in children: impact of the underlying disease

Glucocorticoids inhibit osteoblasts through multiple mechanisms, which results in significant reductions in bone formation. The growing skeleton may be especially vulnerable to adverse glucocorticoid effects on bone formation, which could possibly compromise trabecular and cortical bone accretion. Although decreased bone mineral density has been described in various pediatric disorders that require glucocorticoids, and a population-based study reported increased fracture risk in children who require >4 courses of glucocorticoids, some of the detrimental bone effects attributed to glucocorticoids may be caused by the underlying inflammatory disease. For example, inflammatory cytokines that are elevated in chronic disease, such as tumor necrosis factor alpha, suppress bone formation and promote bone resorption through mechanisms similar to glucocorticoid-induced osteoporosis. Summarized in this review are changes in bone density and dimensions during growth, the effects of glucocorticoids and cytokines on bone cells, the potential confounding effects of the underlying inflammatory-disease process, and the challenges in interpreting dual-energy x-ray absorptiometry results in children with altered growth and development in the setting of glucocorticoid therapy. Two recent studies of children treated with chronic glucocorticoids highlight the differences in the effect of underlying disease, as well as the importance of associated alterations in growth and development.

Fracture rate in children with cerebral palsy

OBJECTIVES

To determine the prevalence of previous fracture, the rate of fracture over time and associated risk factors for fracture in children with moderate or severe cerebral palsy (CP).

STUDY DESIGN

Three hundred and sixty-four children with moderate-to-severe motor impairment (Gross Motor Function Classification System III, IV and V) enrolled in a multi-centre, region-based longitudinal study of growth, nutrition and health. Of these, 297 had baseline fracture information and 261 children had at least one follow-up assessment. Median duration of follow-up was 1.6 years, for over 600 person-years of follow-up.

RESULTS

Forty-six (15.5%) children reported 62 previous fractures at baseline assessment. Children with a history of fractures at baseline were older (mean age 11.9 vs. 8.9 years, p<0.0001) and had greater body fat (triceps z-score -0.01 vs. -0.68, p=0.0003) than children with no previous fracture. Twenty children (6.7%) reported 24 fractures during the follow-up period. Factors associated with risk of fracture during the follow-up period were higher body fat (p=0.03), gastrostomy use (p=0.05) and previous fracture (p=0.10). Based on 24 fractures in 604.5 person-years of follow-up, the rate of fracture was 4.0 per hundred children (4.0%) per year. For children with a history of fracture at baseline, the fracture rate was 7.0% per year; for children with gastrostomy, 6.8% per year; and for children with high triceps skinfold, 9.7% per year.

CONCLUSIONS

Children with moderate or severe CP are at high risk for fracture. Children with greater body fat, feeding gastrostomy and prior history of fracture are at highest risk and may benefit most from intervention. Further longitudinal study and clinical trials in children with CP are needed to better understand the factors contributing to fracture risk in this population and the best methods of prevention and treatment.

Racial differences in the association of subcutaneous and visceral fat on bone mineral content in prepubertal children

Total fat mass plays a significant role in determining bone mass, but the specific role of central adiposity independent of total fat mass has not been widely studied. Prepubertal (Tanner 1) children (n = 181; 65 boys, 116 girls, 7.8 +/- 1.5 years), including 99 Caucasians and 82 African Americans from Birmingham, Alabama, participated in this study. Body composition, including total body and trunk fat mass, and bone mineral content (BMC) were measured using dual-energy X-ray absorptiometry. Subcutaneous abdominal adipose tissue (SAAT) and intra-abdominal adipose tissue (IAAT) were determined by single-slice computed tomography (CT). After adjusting for gender, age, height, total fat, and lean mass, trunk weight was inversely correlated with BMC in Caucasians (r = -0.56, P < 0.0001) and in African Americans (r = -0.37, P < 0.05). In Caucasians, independent of gender, age, height, total fat, and lean mass, there was an inverse correlation between SAAT and BMC (r = -0.58, P < 0.0001) but no significant correlation between IAAT and BMC; in addition, SAAT explained 6% of the variance in BMC. In contrast, in African Americans, SAAT and BMC were not significantly correlated. However, while adjusting for gender, age, height, SAAT, total fat, and lean mass, an inverse association between IAAT and BMC was observed in African Americans (r = -0.50, P < 0.01); IAAT also explained 3% of the variance in BMC. These findings suggest that, in general, total abdominal weight is negatively associated with bone mass, but there appear to be racial differences with regard to the contributions of subcutaneous and visceral fat to BMC in prepubertal children.

Nutrition and bone growth and development

The growth and development of the human skeleton requires an adequate supply of many different nutritional factors. Classical nutrient deficiencies are associated with stunting (e.g. energy, protein, Zn), rickets (e.g. vitamin D) and other bone abnormalities (e.g. Cu, Zn, vitamin C). In recent years there has been interest in the role nutrition may play in bone growth at intakes above those required to prevent classical deficiencies, particularly in relation to optimising peak bone mass and minimising osteoporosis risk. There is evidence to suggest that peak bone mass and later fracture risk are influenced by the pattern of growth in childhood and by nutritional exposures in utero, in infancy and during childhood and adolescence. Of the individual nutrients, particular attention has been paid to Ca, vitamin D, protein and P. There has also been interest in several food groups, particularly dairy products, fruit and vegetables and foods contributing to acid-base balance. However, it is not possible at the present time to define dietary reference values using bone health as a criterion, and the question of what type of diet constitutes the best support for optimal bone growth and development remains open. Prudent recommendations (Department of Health, 1998; World Health Organization/Food and Agriculture Organization, 2003) are the same as those for adults, i.e. to consume a Ca intake close to the reference nutrient intake, optimise vitamin D status through adequate summer sunshine exposure (and diet supplementation where appropriate), be physically active, have a body weight in the healthy range, restrict salt intake and consume plenty of fruit and vegetables.

Fractures and recurrent fractures in children; varying effects of environmental factors as well as bone size and mass

BACKGROUND

Fractures are frequent in childhood and cause considerable morbidity. Previous reports have indicated a variety of potential contributors to fracture risk including low bone mineral content and density, milk avoidance, lack of exercise, asthma, obesity, and a high consumption of carbonated beverages.

AIMS

We wished to test the hypothesis that children who sustain recurrent fractures have a lower bone mass and a higher prevalence of underlying risk factors for fracture than those who fracture once or not at all.

METHODS

We studied 150 children aged 4-16 years: 50 who had suffered recurrent fractures, 50 who had fractured for the first time, and 50 fracture-free controls. Subjects underwent assessment of bone size and mass by total body (TB) and lumbar spine (L2-4) dual energy X-ray absorptiometry (DXA). Values were adjusted for body size, based on the control group measurements as unadjusted DXA values are substantially influenced by size in children. Anthropometry and grip dynamometry were carried out, and information about factors implicated in fracture aetiology such as milk intake, physical activity levels, asthma prevalence and carbonated beverage consumption were recorded using questionnaires.

RESULTS

Children who had sustained one or more fractures had a significantly lower BMC and aBMD at all sites than controls after conversion to size adjusted z scores (L2-4 BMC P = 0.0002; L2-4 aBMD P < 0.0001; TB BMC P < 0.0001; TB aBMD P < 0.0001); estimates for TB excluded fracture sites. There was, however, no difference in adjusted bone mass between children with one and those with recurrent fractures. Children with recurrent fractures had a significantly lower milk intake, lower levels of physical activity, a higher BMI, and a higher consumption of carbonated beverages than controls. The prevalence of risk factors was not, however, significantly higher than controls in children with a single fracture.

CONCLUSIONS

Children with fractures have a lower bone mass for body size than children without fractures. Modifiable risk factors such as diet and exercise increase the risk of recurrent fractures.

Association between bone mass and fractures in children: a prospective cohort study

This is the first prospective cohort study of the association between bone mass and fracture risk in childhood. A total of 6213 children 9.9 years of age were followed for 24 months. Results showed an 89% increased risk of fracture per SD decrease in size-adjusted BMC.

INTRODUCTION

Although previous case-control studies have reported that fracture risk in childhood is inversely related to bone mass, this has not been confirmed in prospective studies. Additionally, it remains unclear which constituent(s) of bone mass underlie this association. We carried out a prospective cohort study to examine the relationship between DXA measures in children 9.9 years of age and risk of fracture over the following 2 years.

MATERIALS AND METHODS

Total body DXA scan results obtained at 9.9 years of age were linked to reported fractures over the following 2 years in children from a large birth cohort in southwest England. DXA measures consisted of total body less head (TBLH) BMD, bone area, and BMC, and results of subregional analysis of the humerus. Analyses were adjusted for age, sex, ethnicity, and social position.

RESULTS

Complete data were available on 6213 children. There was a weak inverse relationship between BMD at 9.9 years and subsequent fracture risk (OR per SD decrease = 1.12; 95% CI, 1.02-1.25). In analyses examining the relationship between fracture risk and volumetric BMD, fracture risk was inversely related to BMC adjusted for bone area, height, and weight (OR = 1.89; 95% CI, 1.18-3.04) and to estimated volumetric BMD of the humerus (OR = 1.29; 95% CI, 1.14-1.45). Fracture risk was unrelated to both TBLH and humeral bone area. However, in analyses of the relationship between fracture risk and bone size relative to body size, an inverse association was observed between fracture risk and TBLH area adjusted for height and weight (OR = 1.51; 95% CI, 1.17-1.95).

CONCLUSIONS

Fracture risk in childhood is related to volumetric BMD, reflecting an influence of determinants of volumetric BMD such as cortical thickness on skeletal fragility. Although bone size per se was not related to fracture risk, we found that children who fracture tend to have a smaller skeleton relative to their overall body size.

Pediatric Obesity: Impact and Surgical Management

The incidence of children in the United States who are overweight or obese is increasing at an alarming rate, and many obesity-related complications are now being described in children. There appears to be no current pharmacologic treatment or surgical procedure that is both safe and effective for millions of obese children. Bariatric surgery may be useful, however, in carefully selected obese children with associated serious comorbidities unresponsive to medical or dietary interventions. The complications of pediatric obesity are discussed, as well as current medical and surgical management of this disorder.

Adipose tissue stimulates bone growth in prepubertal children

CONTEXT

Fat mass represents a positive influence on bone mass in adults, independently of other factors such as lean mass, but whether a similar action occurs in children is unclear.

OBJECTIVE

Our objective was to examine the relationship between fat mass and bone mass in children.

DESIGN AND SETTING

We conducted combined cross-sectional and prospective analyses at university research clinics.

PARTICIPANTS

Participants included children aged 9.9 yr from a large population-based birth cohort in southwest England.

OUTCOMES

Relationships between total body fat mass were measured by dual-energy x-ray absorptiometry at age 9.9 yr, and 1) total-body-less-head bone mass and area at age 9.9 and 2) increase in bone mass and area over the following 2 yr.

RESULTS

There was a strong positive relationship between total body fat mass and total-body-less-head bone mass and area, even after adjustment for height and/or lean mass (P < 0.001). There was a similar positive association between total body fat mass and increase in bone mass and area over the following 2 yr in boys and Tanner stage 1 girls. In contrast, no association was present between fat mass and gain in bone mass and size in Tanner stage 2 girls, whereas a negative association was seen in Tanner stage 3 girls (puberty-fat mass interaction, P < 0.001).

CONCLUSIONS

In prepubertal children, fat mass is a positive independent determinant of bone mass and size and of increases in these parameters over the following 2 yr, suggesting that adipose tissue acts to stimulate bone growth. However, this relationship is attenuated by puberty.

The impact of childhood obesity on musculoskeletal form

Despite the greater prevalence of musculoskeletal disorders in obese adults, the consequences of childhood obesity on the development and function of the musculoskeletal system have received comparatively little attention within the literature. Of the limited number of studies performed to date, the majority have focused on the impact of childhood obesity on skeletal structure and alignment, and to a lesser extent its influence on clinical tests of motor performance including muscular strength, balance and locomotion. Although collectively these studies imply that the functional and structural limitations imposed by obesity may result in aberrant lower limb mechanics and the potential for musculoskeletal injury, empirical verification is currently lacking. The delineation of the effects of childhood obesity on musculoskeletal structure in terms of mass, adiposity, anthropometry, metabolic effects and physical inactivity, or their combination, has not been established. More specifically, there is a lack of research regarding the effect of childhood obesity on the properties of connective tissue structures, such as tendons and ligaments. Given the global increase in childhood obesity, there is a need to ascertain the consequences of persistent obesity on musculoskeletal structure and function. A better understanding of the implications of childhood obesity on the development and function of the musculoskeletal system would assist in the provision of more meaningful support in the prevention, treatment and management of the musculoskeletal consequences of the condition.

Sex difference in the effect of puberty on the relationship between fat mass and bone mass in 926 healthy subjects, 6 to 18 years old

OBJECTIVE

Understanding factors influencing bone mineral accrual is critical to optimize peak bone mass during childhood. The epidemic of pediatric obesity and reported higher incident of fracture risk in obese children led us to study the influence of fat mass on bone mineral content (BMC) in children.

RESEARCH METHODS AND PROCEDURES

Height; weight; pubertal stage; and BMC, non-bone fat-free mass (nbFFM), and fat mass (FM) by DXA were obtained in a multiethnic group of healthy children (444 girls/482 boys; 6 to 18 years old) recruited in the New York metropolitan area. Regression techniques were used to explore the relationship between BMC and FM, with age, height, nbFFM, pubertal stage, sex, and ethnicity as covariates.

RESULTS

Because there were significant sex interactions, separate regression analyses were performed for girls and boys. Although ln(nbFFM) was the greatest predictor of ln(BMC), ln(FM) was also a significant predictor in prepubertal boys and all girls but not in pubertal boys. This effect was independent of ethnicity.

DISCUSSION

FM was a determinant of BMC in all girls but in only prepubertal boys. Our study confirms nbFFM as the greatest predictor of BMC but is the first to find a sex difference in the effect of puberty on the relationship of FM to BMC. Our results suggest that, in two individuals of the same sex and weight, the one with greater fat mass will have lower BMC, especially pubertal boys. The implications of these findings for achievement of optimal peak bone mass in a pediatric population with an unprecedented incidence of overweight and "overfat" status remain to be seen.

Effects of childhood obesity on three-dimensional knee joint biomechanics during walking

Despite the increasing percentages of children who are overweight, few studies have investigated their gait patterns. The purpose of this study was to quantify the three-dimensional knee joint kinematics and kinetics during walking in children of varying body mass and to identify effects associated with obesity. Three-dimensional kinematics and kinetics were collected from children of normal weight and overweight during normal gait using surface-mounted infrared emitting diodes and a force plate. The overweight group walked with a significantly lower peak knee flexion angle during early stance, and no significant differences in peak internal knee extension moments were found between groups. However, the overweight group showed a significantly higher peak internal knee abduction moment during early stance. These data suggest that although overweight children may develop a gait adaptation to maintain a similar knee extensor load, they may not be able to compensate for alterations in the frontal plane, which may lead to increased medial compartment joint loads. Therefore, assuming that the development of varus angular deformities of the knee joint and, in the longer term, medial compartment osteoarthritis are influenced by cumulative stress, this study supports the understanding that childhood obesity may impart a greater risk for the development of these diseases.

Evaluation of bone density in children with slipped capital femoral epiphysis

Slipped capital femoral epiphysis (SCFE) is a condition seen during the preadolescent growth spurt, often in obese children and in children with endocrine disorders. Given that endocrine factors also play a role in bone density, a link between low bone mineral density (BMD) and SCFE was proposed. Dual energy X-ray absorptiometry (DXA) scanning of the spine and hips was performed on 12 children with SCFE and on 5 overweight children without this hip disorder. All scans were performed by the same technician using a Hologic Delphi W densitometer and were interpreted by a pediatric orthopedic surgeon certified in clinical densitometry. Z-scores were obtained using a pediatric database. Mean and standard deviation of the Z-scores were calculated, and paired t tests were used to assess differences between these subjects and the expected norm. The SCFE patients' Z-scores at each of the skeletal sites assessed (spine, femoral neck, and total hip) were greater than the mean by an average of 1 standard deviation. The control subjects' BMD was also greater than the mean. The P values were less then 0.05. These results suggest that children with SCFE do not have low BMD, but show bone density significantly greater then expected for age and sex. Although BMD is endocrinologically driven and endocrinologic abnormalities are implicated in SCFE, there appears to be no correlation between low BMD and SCFE.

Optimizing bone health and calcium intakes of infants, children, and adolescents

Most older children and adolescents in the United States currently do not achieve the recommended intake of calcium. Maintaining adequate calcium intake during childhood and adolescence is necessary for the development of peak bone mass, which may be important in reducing the risk of fractures and osteoporosis later in life. Optimal calcium intake is especially relevant during adolescence, when most bone mineral accretion occurs. Because of the influence of the family's diet on the diet of children and adolescents, adequate calcium intake by all members of the family is important. Assessment of calcium intake can be performed in the physician's office. A well-rounded diet including low-fat dairy products, fruits, and vegetables and appropriate physical activity are important for achieving good bone health. Establishing these practices in childhood is important so that they will be followed throughout the life span.

The relative contributions of lean tissue mass and fat mass to bone density in young women

Although obesity is associated with increased risk of many chronic diseases including cardiovascular disease, diabetes, hypertension, and cancer, there is little evidence to suggest that obesity increases risk of osteoporosis. In fact, both weight and body mass index (BMI) are positive predictors of bone mass in adults, suggesting that those who are overweight or obese may be at lower risk of osteoporosis. However, recent evidence suggests that in children and adolescents, obesity may be associated with lower rather than higher bone mass. To understand the relation of fat mass to bone mass, we examined data gathered from an ethnically diverse group of 921 young women, aged 20-25 years (317 African Americans, 154 Asians, 322 Caucasians, and 128 Latinas) to determine how fat mass (FM) as well as lean tissue mass (LTM) is associated with bone mass. Bone mass, FM, and LTM were measured using dual energy X-ray absorptiometry (GE Lunar Corp, Madison, WI). Bone mass was expressed as bone mineral density (BMD; g/cm2) and bone mineral apparent density (BMAD; g/cm3) for the spine and femoral neck, and as BMD and bone mineral content (BMC; g) for the whole body. Regression techniques were used to examine the following: (1) in separate equations, the associations of LTM and FM with each bone mass parameter; and (2) in the same equation, the independent contributions of LTM and FM to bone mass. LTM and FM were positively correlated with BMD at all skeletal sites. When the contributions of FM and LTM were examined simultaneously, both FM and LTM continued to be positively associated with bone mass parameters but the effect of FM was noted to be smaller than that of LTM. We conclude that in young women, LTM has a greater effect than fat mass on bone density per kg of tissue mass.

Do young New Zealand Pacific Island and European children differ in bone size or bone mineral?

Although Pacific Island adults have been shown to have larger bones and greater bone mineral density than caucasians, no previous studies have been undertaken to determine whether differences are present in prepubertal children. Forty-one Pacific Island children (both parents of Pacific Island descent) and 38 European children, aged 3 to 7 years, living in New Zealand were studied. Heights and weights were determined by simple anthropometry and body mass index (BMI, kg/m2) was calculated. Body composition, bone size, and bone mineral content (BMC, g) were measured by dual energy X-ray absorptiometry (DXA) of the total body and the non-dominant forearm. Compared to European children, in data adjusted for age and gender, Pacific Island children had significantly greater (P < 0.05) BMC in the total body (12%), the ultradistal radius (16%), and the 33% radius (8%), and also greater total body bone area (10%). Bone mineral density (BMD, g/cm2) was higher only at the ultradistal radius (11%). However, after adjustment for body weight, in particular lean mass, no differences were seen between Pacific Island and European children in any bone measure. The larger bone area and BMC of young Pacific Island children can be explained by their greater height and weight. Therefore, this study has shown that prepubertal Pacific Island children do not have greater bone size or BMC for their weight.

Composition of the fat-free mass in obese and nonobese children: matched case-control analyses

OBJECTIVE

Most body composition techniques assume constant properties of the fat-free mass (FFM), such as hydration, density and mineralisation. Previous studies suggested that FFM composition may change in childhood obesity; however, this issue has not been investigated in detail.

AIM

To compare FFM composition in obese and nonobese children.

DESIGN

Observational matched case-control analyses.

SUBJECTS

A total of 28 obese children (13 boys, 15 girls) and 22 nonobese children (10 boys, 12 girls) aged 7-14 y. Obesity was defined as body mass index centile >95.

METHODS

Measurements were made of weight, height, total body water, and body volume. Bone mineral content was estimated in a subsample. Body composition was calculated using three- and four-component models.

RESULTS

According to the three-component model (n=22 matched pairs), obese children had greater hydration (P<0.05), and reduced density (P=0.057) of FFM. According to the four component model (n=11 pairs), obese children had greater hydration (P<0.01) and reduced density (P<0.002) of FFM. The mineralisation of FFM was increased, but not significantly so.

CONCLUSION

The greater hydration and reduced density of FFM of obese children should be taken into account if body composition is to be measured with optimum accuracy during treatment programmes. These differences may be addressed by using multicomponent rather than two-component models of body composition. Although the greater mineralisation of FFM in obese children was not significant in the present study, the four-component model is best able to address the combined differences in hydration and mineralisation that occur in childhood obesity.

Assessment of bone mass following renal transplantation in children

Throughout childhood and adolescence, skeletal growth results in site-specific increases in trabecular and cortical dimensions and density. Childhood osteoporosis can be defined as a skeletal disorder characterized by compromised bone strength predisposing to an increased risk of fracture. Pediatric renal transplant recipients have multiple risk factors for impaired bone density and bone strength, including pre-existing renal osteodystrophy, delayed growth and development, malnutrition, decreased weight-bearing activity, inflammation, and immunosuppressive therapies. Dual energy X-ray absorptiometry (DXA) is the most-common method for the assessment of skeletal status in children and adults. However, DXA has many important limitations that are unique to the assessment of bone health in children. Furthermore, DXA is limited in its ability to distinguish between the distinct, and sometimes opposing, effects of renal disease on cortical and trabecular bone. This review summarizes these limitations and the difficulties in assessing and interpreting bone measures in pediatric transplantation are highlighted in a review of select studies. Alternative strategies are presented for clinical and research applications.

(n-3) fatty acids reduce the release of prostaglandin E2 from bone but do not affect bone mass in obese (fa/fa) and lean Zucker rats

Childhood obesity is prevalent and linked to the development of Type 2 diabetes mellitus (DM) and poor bone health. Some PUFA enhance bone mass and thus may improve bone health in obese children. The study objective was to determine the effects of dietary (n-6) compared with (n-3) essential PUFA and long-chain PUFA (LCPUFA) on bone in an obese and insulin-resistant state. Male fa/fa (n = 48) and lean Zucker rats (n = 48) were fed diets containing safflower oil [SO, high (n-6) PUFA], flaxseed oil [FXO, high (n-3) PUFA], or menhaden oil [MO, high (n-3) LCPUFA] for 9 wk. Measurements included the following: femur bone area (BA), mineral content (BMC), density (BMD), morphometry and ex vivo release of prostaglandin E(2) (PGE(2)); plasma osteocalcin and C-terminal telopeptides of type I collagen. Differences among groups were detected using 2-way ANOVA. Genotype effects in the fa/fa rats included lower femoral weight, length, BA, and BMC, as well as femoral head and proximal epiphysis widths compared with the lean rats, but BMD was not affected. Femur BA, BMC, and BMD did not differ among the dietary groups, but diaphysis width was elevated in the MO group and PGE(2) release was reduced by the FXO and MO diets. No genotype x diet interactions were observed. These data indicate that the fa/fa Zucker rat is at risk for low bone mass and that dietary (n-3) FA effectively reduce PGE(2) release. Whether reduced PGE(2) will support optimal peak bone mass during childhood and conserve bone mass with aging warrants investigation.

Proximal femur bone geometry is appropriately adapted to lean mass in overweight children and adolescents

It is unclear if the bones of overweight children are appropriately adapted to increased loads. The objective of this study was to compare bone geometry in 40 overweight (body mass index [BMI] > 85th percentile) and 94 healthy weight (BMI < or = 85th percentile) subjects, ages 4-20 years. Dual energy X-ray absorptiometry (Hologic QDR 2000) scans were analyzed at the femoral shaft (FS) and narrow neck (NN) by the Hip Structure Analysis program. Subperiosteal width, cortical thickness and indices of bone axial and bending strength (bone cross-sectional area [CSA] and section modulus [Z]) were measured from bone mass profiles. Multivariate regression models were used to compare overweight and healthy weight subjects. Z was 11 (95% CI 5, 19) and 13 (7, 20) percent higher at the FS and NN, respectively, in overweight subjects (P < 0.001), adjusted for height, maturation and gender. At the NN, higher Z was due to greater subperiosteal width [4% (2, 7)] and bone CSA [10% (5, 16]) and at the FS, to higher bone CSA [10% (5, 16)] and thicker cortices [9% (3, 15)]. When lean mass was added to the models, bone variables did not differ between overweight and healthy weight subjects (P > 0.22), with the exception of NN subperiosteal width [3% (0, 6), P = 0.04]. Fat mass did not contribute significantly to any model. In summary, proximal femur bone geometric strength in overweight children was appropriately adapted to lean mass and height but greater weight in the form of fat mass did not have an independent effect on bone bending strength. These geometric adaptations are consistent with the mechanostat hypothesis that bone strength adapts primarily to muscle forces, not to static loads represented by body weight.

Postural instability of extremely obese individuals improves after a body weight reduction program entailing specific balance training

The purposes of this study were to compare postural stability between obese and lean subjects and to investigate the effect of a 3-week body weight reduction (BWR) program entailing specific balance training on postural stability of extremely obese patients. Time of balance maintenance and mean error on the medial-lateral direction at the trunk and lower limb level were assessed during a single limb stance on a movable platform in 19 non-obese and in 20 extremely obese individuals (age range: 20-40 yr). Time of balance maintenance was shorter (obese: 21.1+/-7.7 vs lean: 27.3+/-3.1 sec) and medial-lateral sway of the trunk was larger in obese (5.4+/-3.2 degrees) than in lean (3.2+/-1.1 degrees) subjects (p<0.05). Two subgroups of obese subjects were also tested after a BWR program (energy-restricted diet, moderate physical exercise, nutritional education and psychological counselling) combined with or without 6 sessions of specific balance training on a movable platform. BWR plus specific balance training enhanced time of balance maintenance (pre: 23.8+/-7.2 vs post: 30.0+/-0.0 sec) and reduced the trunk sway (5.2+/-2.8 degrees vs 2.6+/-0.9 degrees ) more than BWR alone (p<0.05). The present findings indicate that extremely obese individuals have inadequate postural stability (compared to their lean counterparts) that could however be improved by few sessions of specific balance training incorporated into a multidisciplinary BWR program. It was concluded that balance improvement is an important goal of rehabilitation, that would probably reduce the propensity of overweight individuals to fall while performing everyday activities.

Percentile distributions of bone measurements in Iowa children: the Iowa Bone Development Study

Four hundred twenty-eight white children (200 boys and 228 girls) ages 4.5-6.5 yr had spine, hip, and whole-body bone mineral density (BMD) and bone mineral content (BMC) measured by dual-energy X-ray absorptiometry(DXA) as part of the Iowa Bone Development Study. Anthropometric measurements, including height, weight, and body mass index (BMI) were determined for each child at the time the bone measurements were made. The age- and gender-specific height percentile based on the 2000 CDC Growth Charts (www.cdc.gov/growthcharts/) was determined for each child. These percentiles were used to classify children into four groups as defined by the 25th, 50th,and 75th percentile cutpoints. Percentile distributions were determined within each height quartile group to delineate percentiles (5th, 25th, 50th, 75th, 95th) for BMD and BMC. Gender differences in BMD and BMC were investigated before and after stratification into height groups. Boys had higher age-height-weight-adjusted means for most BMD and BMC measures except spine BMD. Bone measurements increased with height quartile, indicating that taller children have greater BMD and BMC compared to shorter children of the same age and gender. Within any given quartile,mean BMD and BMC measurements were similar for boys and girls, with the exception of hip BMD, for which values were consistently higher for boys (p < 0.05). In addition, whole-body BMC values were higher for boys in quartiles 1 and 3 (p < 0.05). These bone measures provide norms for young white children and serve as a reference for comparison with other racial and ethnic groups, as well as with childhood populations that are at risk for osteopenia because of chronic disease. Gender, age, and height are useful clinical predictors of BMD and BMC in young children.

Growth, children, and fractures

Fractures in childhood have long been considered an unavoidable consequence of growth. Studies in recent years have documented the epidemiology of these very common fractures and have also documented considerable variation by fracture type and from country to country. There have also been a number of studies aimed at identifying risk factors particularly for the most common distal forearm fracture. These studies have consistently associated bone mineral density with these fractures. Other possible risk factors include obesity, physical inactivity, sports, cola beverages, calcium intake, risk taking, and coordination. While prospective studies are required to confirm these risk factors, accumulating evidence now suggests that a substantial proportion of fractures in children are preventable.

Obesity during childhood and adolescence augments bone mass and bone dimensions

BACKGROUND

Studies of the effect of childhood obesity on bone accrual during growth have yielded conflicting results, largely related to the failure to adequately characterize the confounding effects of growth, maturation, and body composition.

OBJECTIVE

The objective of this study was to determine the effect of childhood obesity on skeletal mass and dimensions relative to height, body composition, and maturation in males and females.

DESIGN

In 132 nonobese (body mass index < 85th percentile) and 103 obese (body mass index > or = 95th percentile) subjects aged 4-20 y, whole-body and vertebral bone mineral content (BMC) was determined by using dual-energy X-ray absorptiometry, and bone area, areal bone mineral density (BMD), and fat and lean masses were measured. Vertebral volumetric BMD was estimated as BMC/area(1.5).

RESULTS

Obesity was associated with greater height-for-age, advanced maturation for age, and greater lean mass for height (all P < 0.001). Sex-specific multivariate regressions with adjustment for maturation showed that obesity was associated with greater vertebral areal BMD for height, greater volumetric BMD, and greater vertebral BMC for bone area (all P < 0.05). After adjustment for maturation and lean mass, obesity was associated with significantly greater whole-body bone area and BMC for age and for height (all P < 0.001).

CONCLUSIONS

In contrast with the results of prior studies, obesity during childhood and adolescence was associated with increased vertebral bone density and increased whole-body bone dimensions and mass. These differences persisted after adjustment for obesity-related increases in height, maturation, and lean mass. Future studies are needed to determine the effect of these differences on fracture risk.

Interpretation of whole body dual energy X-ray absorptiometry measures in children: comparison with peripheral quantitative computed tomography

The assessment of bone health in children requires strategies to minimize the confounding effects of bone size on dual energy X-ray absorptiometry (DXA) areal bone mineral density (BMD) results. Cortical bone composes 80% of the total skeletal bone mass. The objective of this study was to develop analytic strategies for the assessment of whole body DXA that describe the biomechanical characteristics of cortical bone across a wide range of body sizes using peripheral quantitative computed tomography (pQCT) measures of cortical geometry, density (mg/mm(3)), and strength as the gold standard. Whole body DXA (Hologic QDR 4500) and pQCT (Stratec XCT-2000) of the tibia diaphysis were completed in 150 healthy children 6-21 years of age. To assess DXA and pQCT measures relative to age, body size, and bone size, gender-specific regression models were used to establish z scores for DXA bone mineral content (BMC) for age, areal BMD for age, bone area for height, bone area for lean mass, BMC for height, BMC for lean mass, and BMC for bone area; and for pQCT, bone cross-sectional area (CSA) for tibia length and bone strength (stress-strain index, SSI) for tibia length. DXA bone area for height and BMC for height were both strongly and positively associated with pQCT CSA for length and with SSI for length (all P < 0.0001), suggesting that decreases in DXA bone area for height or DXA BMC for height represent narrower bones with less resistance to bending. DXA BMC for age (P < 0.01) and areal BMD (P < 0.05) for age were moderately correlated with strength. Neither DXA bone area for lean mass nor BMC for lean mass correlated with pQCT CSA for length or SSI for length. DXA BMC for bone area was weakly associated with pQCT SSI for length, in females only. Therefore, normalizing whole body DXA bone area for height and BMC for height provided the best measures of bone dimensions and strength. DXA BMC normalized for bone area and lean mass were poor indicators of bone strength.

Bone disease in pediatric rheumatologic disorders

Children with rheumatic disorders have multiple risk factors for impaired bone health, including delayed growth and development, malnutrition, decreased weight-bearing activity, inflammation, and glucocorticoid therapy. The impact of rheumatic disease during childhood may be immediate, resulting in fragility fractures, or delayed, because of suboptimal peak bone mass accrual. Recent years have seen increased interest in the effects of pediatric rheumatic disorders on bone mineralization, such as juvenile rheumatoid arthritis, systemic lupus erythematosus, and juvenile dermatomyositis. This review outlines the expected gains in bone size and mass during childhood and adolescence, and summarizes the advantages and disadvantages of available technologies for the assessment of skeletal growth and fragility in children. The varied threats to bone health in pediatric rheumatic disorders are reviewed, with emphasis on recent insights into the molecular mechanisms of inflammation-induced bone resorption. The literature assessing bone deficits and risk factors for impaired bone health in pediatric rheumatic disorders is reviewed, with consideration of the strengths and limitations of prior studies. Finally, future research directions are proposed.

Orthopedic complications of childhood obesity

PURPOSE

The purpose of this article is to describe the orthopedic problems known to be associated with being overweight or obese during childhood to assist the clinician in the evaluation and management of these patients.

SUMMARY OF KEY POINTS

Children who are overweight or obese are becoming an increasing concern in our society; the number of children and teens described as overweight or obese tripled from 1980 to 2000. Many problems have been associated with obesity and are well described in the literature, including cardiovascular problems, diabetes mellitus, liver complications, cholelithiasis, sleep apnea, and specific types of cancer. Orthopedic complications are also related to being overweight or obese during childhood. Specifically, the incidence of spinal complications, slipped capital femoral epiphysis, Blount disease, and acute fractures has been related to being overweight or obese.

CONCLUSIONS

Clinicians should be aware of the orthopedic problems related to obesity to better educate individuals as well as to better treat children with this condition.

Leptin and bone mineral density: a cross-sectional study in obese and nonobese men

Leptin has been suggested to decrease bone mineral density (BMD). This observational analysis explored the relationship between serum leptin and BMD in 327 nonobese men (controls) (body mass index 26.1 +/- 3.7 kg/m(2), age 49.9 +/- 6.0 yr) and 285 juvenile obese men (body mass index 35.9 +/- 5.9 kg/m(2), age 47.5 +/- 5.1 yr). Whole-body dual-energy x-ray absorptiometry scan measured BMD, fat mass, and lean mass. Fasting serum leptin (nanograms per milliliter) was strongly associated with fat mass (kilograms) in both controls (r = 0.876; P < 0.01) and juvenile obese (r = 0.838; P < 0.001). An inverse relation between BMD adjusted for body weight and serum leptin emerged in both the control group (r = -0.186; P < 0.01) and the juvenile obese group (r = -0.135; P < 0.05). In a multiple linear regression, fat mass, lean body mass, and occupational physical activity were positively associated with BMD in the control group, whereas in the juvenile obese, only lean body mass was positively associated with BMD and smoking negatively associated with BMD. Our study supports that leptin is inversely associated with BMD and may play a direct role in the bone metabolism in nonobese and obese Danish males, but it also stresses the fact that the strong covariation between the examined variables is a shortcoming of the cross-sectional design.

Biomechanical analysis of arm fracture in obese boys

OBJECTIVE

To determine the role of the biomechanical factors of force of impact, bone strength, fall height and surface stiffness on the risk of forearm fracture in obese children compared to non-obese children.

METHODOLOGY

Anthropometric and dual-energy X-ray absorptiometry bone density data from 50 boys (25 obese pair-matched with 25 non-obese subjects) aged 4-17 years were entered into a rheological-stochastic simulation model of arm impact.

RESULTS

Obese children were shown to be at 1.7 times greater risk of fracture compared to non-obese children. Lower fall heights and softer impact surfaces were found not to reduce the relative risk of fracture between obese and non-obese children.

CONCLUSIONS

Environmental modifications are unlikely to lower the risk of arm fracture in obese children to the same levels experienced by non-obese children. The best option available for obese children to reduce fracture risk is to take steps to attain a healthy bodyweight.

Comparison of body composition methods in overweight and obese children

The objective of the present study was to investigate the accuracy of percent body fat (%fat) estimates from dual-energy X-ray absorptiometry, air-displacement plethysmography (ADP), and total body water (TBW) against a criterion four-compartment (4C) model in overweight and obese children. A volunteer sample of 30 children (18 male and 12 female), age of (mean ± SD) 14.10 ± 1.83 yr, body mass index of 31.6 ± 5.5 kg/m, and %fat (4C model) of 41.2 ± 8.2%, was assessed. Body density measurements were converted to %fat estimates by using the general equation of Siri (ADPSiri) (Siri WE. Techniques for Measuring Body Composition. 1961) and the age- and gender-specific constants of Lohman (ADPLoh) (Lohman TG. Exercise and Sport Sciences Reviews. 1986). TBW measurements were converted to %fat estimates by assuming that water accounts for 73% of fat-free mass (TBW73) and by utilizing the age- and gender-specific water contents of Lohman (TBWLoh). All estimates of %fat were highly correlated with those of the 4C model ( r ≥ 0.95, P < 0.001; SE ≤ 2.14). For %fat, the total error and mean difference ± 95% limits of agreement compared with the 4C model were 2.50, 1.8 ± 3.5 (ADPSiri); 1.82, -0.04 ± 3.6 (ADPLoh); 2.86, -2.0 ± 4.1 (TBW73); 1.90, -0.3 ± 3.8 (TBWLoh); and 2.74, 1.9 ± 4.0 DXA (dual-energy X-ray absorptiometry), respectively. In conclusion, in overweight and obese children, ADPLoh and TBWLoh were the most accurate methods of measuring %fat compared with a 4C model. However, all methods under consideration produced similar limits of agreement.

Effect of sub-elite competitive running on bone density, body composition and sexual maturity of adolescent females

The attainment of optimal peak bone mass during adolescence is important in the primary prevention of osteoporosis. Exercise may contribute to skeletal development and bone density during growth, although competitive exercise is suggested to have an adverse effect. This study assesses the effect of moderate exercise on the bone density of adolescent females. Additionally, other factors which significantly influence attainment of peak bone mass were identified. This was a cross-sectional study of 42 adolescent females, classified as runners (n=15) or non-runners (n=27). Nutrient intake, energy expenditure, menstrual history and pubertal stage were recorded. Bone age, skinfold thickness, body composition and bone mineral density (BMD) of total body, lumbar spine and proximal femur were measured. Statistical analyses used Student's t-test, Pearson correlation and multiple regression analyses. Runners had lower fat mass and higher lean mass, with a trend to higher BMD in all sites measured. There were no significant differences in menstrual cycle regularity, age at menarche or number who had attained menarche. Pubic hair development was similar in both groups. Breast development was delayed in runners, although this may have been a function of lower fat mass in this group. When subjects were categorized according to menarchal status, postmenarchal girls were significantly taller and heavier, with higher fat mass and significantly higher total body and lumbar spine BMD. There was no significant relationship between BMD at any site and dietary nutrient intake. Multiple regression analyses, using BMD as the dependent variable, identified running status, pubertal stage, fat mass and lean mass as significant determinants. When BMD/height was used, significant determinants in total body BMD were fat mass, pubertal stage and running status, while in the lumbar spine, only the latter two variables remained significant. In conclusion, body composition, physical activity and sexual maturity were identified as significant determinants of bone density during adolescence. Runners had significantly lower body fat than non-runners, but this did not interfere with hormonal cyclicity, and caused no detriment to their bone density. The results of this study are reassuring, since they indicate that sub-elite competitive athletics has no detrimental effect on bone mass accrual in adolescent females.

Reduced bone mineralization in adolescent survivors of malignant bone tumors: comparison of quantitative ultrasound and dual-energy x-ray absorptiometry

PURPOSE

To assess bone mineralization in adolescents with bone tumors at remission using quantitative digital ultrasound (QUS) and dual-energy x-ray absorptiometry (DEXA), and to compare the bone mineralization values obtained by both methods.

METHODS

Patients studied were 36 adolescents (21 boys, 15 girls) who had completed treatment of a bone tumor at the University Hospital of the University of Navarra (Pamplona, Spain). QUS was performed at the distal metaphysis of the proximal phalanxes of the last four fingers of the nondominant hand. A DBM Sonic 1200 Ultrasound densitometer was used. DEXA measurements were made at the lumbar spine (vertebrae L1-L4) using the Hologic QDR 4500 W device. Calcium and vitamin D daily intake and grade of physical activity were recorded.

RESULTS

Mean age at bone mineralization determination was 19.11 years. Disease-free survival was 4.97 years. Decreased bone mineralization was observed by both methods. Bone mineralization absolute values measured by QUS and DEXA were significantly correlated. The sensitivity, specificity, diagnostic accuracy, and positive and negative predictive values of QUS for predicting osteopenia were 36.4%, 80.0%, 66.7%, 44.4%, and 74.1%, respectively. Daily vitamin D intake was below the recommended dietary allowances.

CONCLUSIONS

Adolescents in remission from bone tumors have low bone mineralization determined by DEXA or QUS.

Dynamic and static tests of balance and postural sway in boys: effects of previous wrist bone fractures and high adiposity

Ninety-three males aged 10-21 years undertook the Bruininks-Oseretsky balance test and two computerized posturography tests to evaluate the effects of (a) previous forearm fracture and (b) high body weight on balance and postural sway. Body composition was measured by dual energy X-ray absorptiometry. Fracture history did not affect balance measures. However, Bruininks-Oseretsky balance scores were negatively correlated with body weight, body mass index, percentage fat and total fat mass. Overweight subjects (n=25) had lower scores (P<0.05) than boys of healthy weight (n=47), supporting the view that overweight adolescents have poorer balance than those of healthy weight.

Body composition of 4- and 5-year-old New Zealand girls: a DXA study of initial adiposity and subsequent 4-year fat change

BACKGROUND

Dual-energy X-ray information (DXA) quantitating body fat mass and percentage fat in healthy children of preschool age is scarce.

OBJECTIVE

To study the initial variability in body composition and subsequent longitudinal changes in absolute fat mass (kg) and relative adiposity (fat percentage) in a sample of contemporary young New Zealand girls.

DESIGN

Cross-sectional study with a longitudinal component.

SETTING

University research unit.

SUBJECTS

A total of 89 Caucasian girls aged 4-5 y were recruited by advertisement at baseline and 4-y changes in body composition were evaluated in 23 of these girls.

METHODS

Total body composition was measured by DXA, height and weight by anthropometry.

RESULTS

Baseline values for fat mass varied more than values for lean mass or bone mass. Girls from the upper third of our fat percentage distribution (% fat >19.2%) had more than twice the fat mass (5.34 vs 2.31 kg, P<0.001) of those from the lowest third (% fat &<15.4%). The percentage gain in fat mass over 4 y (124 (95% CI 90-163) also exceeded the percentage gain of lean mass (55 (95% CI 51-59). In data adjusted for age and height, 63.5% of the variance in percentage body fat at time 2 was explained by fat mass at time one.

CONCLUSIONS

In girls, the trajectory of fat gain appears to be established at a young age. Our results support the view that body fatness tracks strongly before puberty. Since preventing the accumulation of excessive fat is preferable to reduction of existing excessive fat stores, it is important to put in place strategies to limit excessive fat gain early in life.

Bone mineral response to a 7-month randomized controlled, school-based jumping intervention in 121 prepubertal boys: associations with ethnicity and body mass index

We examined the effects of a 7-month jumping intervention (10 minutes, 3 times per week) on bone mineral gain in prepubertal Asian and white boys (10.3+/-0.6 years, 36.0+/-9.2 kg) at 14 schools randomized to control (n = 60) and intervention (n = 61) groups. Intervention and control groups had similar mean baseline and change in height, weight, lean mass and fat mass, baseline areal bone mineral density (aBMD; g/cm2), bone mineral content (BMC; g; dual-energy X-ray absorptiometry [DXA], QDR 4500W), and similar average physical activity and calcium intakes. Over 7 months, the intervention group gained more total body (TB) BMC (1.6%,p < 0.01) and proximal femur (PF) aBMD (1%, p < 0.05) than the control group after adjusting for age, baseline weight, change in height, and loaded physical activity. We also investigated the 41 Asian and 50 white boys (10.2+/-0.6 years and 31.9+/-4.4 kg) who were below the 75th percentile (19.4 kg/m2) of the cohort mean for baseline body mass index (BMI). Boys in the intervention group gained significantly more TB and lumbar spine (LS) BMC, PF aBMD, and trochanteric (TR) aBMD (+ approximately2%) than boys in the control group (adjusted for baseline weight, final Tanner stage, change in height, and loaded physical activity). Bone changes were similar between Asians and whites. Finally, we compared the boys in the control group (n = 16) and the boys in the intervention group (n = 14) whose baseline BMI fell in the highest quartile (10.5+/-0.6 years and 49.1+/-8.2 kg). Seven-month bone changes (adjusted as aforementioned) were similar in the control and intervention groups. In summary, jumping exercise augmented bone mineral accrual at several regions equally in prepubertal Asian and white boys of average or low BMI, and intervention effects on bone mineral were undetectable in high BMI prepubertal boys.