Relationship of BMI z score to fat percent and fat mass in multiethnic prepubertal children.

OBJECTIVE: The objective of the study is to examine the validity of body mass index z score (zBMI) as a measure of percent body fat in prepubertal children. METHODS: One hundred eleven multiethnic, healthy, Tanner 1 children aged 6-12 years had fat percent and fat mass measured by the four-compartment method as part of the Paediatric Rosetta Body Composition Cohort. Multiple regression models were developed with fat percent as the dependent variable and zBMI, age, sex and ethnicity as independent variables. RESULTS: Body mass index z score predicted fat percent, adjusted for age in both girls (P < 0.001, RMSE 5.67 and R2 0.54) and boys (P < 0.001, RMSE 4.71, R2 0.69). The average model percent error was 20.3% in girls and 21.6% in boys. zBMI2 predicted fat mass when adjusted for age and zBMI in both girls (P < 0.001, RMSE 2.27 and R2 0.82) and boys (P < 0.001, RMSE 2.08 and R2 0.81). The average percent error was 7.2% in girls and 8.7% in boys. Age was associated with percentage body fat (P < 0.01), while ethnicity was not (P > 0.05). CONCLUSIONS: Given the relatively large error in the models, zBMI are not a useful indicator of fat mass in healthy, Tanner 1 children. zBMI2 scores are associated with significantly lower absolute percent errors in girls and boys.

Bone mineral in prepubertal children: gender and ethnicity.

Previous reports of gender and ethnic differences in bone mineral in prepubertal children have been inconsistent due to different methodologies, the problematic nature of bone density by dual-energy X-ray absorptiometry (DXA) calculated as the ratio of bone mineral mass to projected bone area (BA), and the generally small study populations. The aim of this study was to test the hypothesis that gender and ethnic differences in bone mineral by DXA are present in prepubertal children. The subjects were 336 healthy Asian, black, and white prepubertal children (172 females and 164 males). Total body bone mineral content (TBBMC) was adjusted for total body BA (TBBA), age, height, and weight. Adjusted mean TBBMC was greater in males than in females (p = 0.01). The gender difference was independent of ethnicity. Adjusted mean TBBMC was different for black compared with nonblack children (p = 0.001). The ethnic difference was a function of TBBA and weight. This study in a multiethnic population of prepubertal children shows (1) a gender difference in TBBMC and (2) an ethnic difference in TBBMC.

Thyrotropin-releasing hormone stimulation tests in infants.

The TSH response to TRH administration (7 micrograms/kg) was measured in 68 infants (22 premature) who had abnormal thyroid screening tests by the filter paper method and whose serum thyroid function tests were only mildly abnormal. Twenty-eight infants (12 premature) had peak TSH values of 35 mU/L or less and were considered normal (group I). Forty infants (10 premature) had peak TSH values above 35 mU/L and were considered hyperresponsive (group II). The mean age at testing, screening T4, TSH levels that prompted the testing, as well as baseline T4, T3, and free T4 at the time of TRH testing were not different between the groups. The mean (+/- SD) baseline TSH value was greater in group II (6.8 +/- 2.3 mU/L) than in group I (4.4 +/- 2.2 mU/L; P < 0.001). However, there was a great deal of overlap in the individual TSH values (group I, 0.9-10 mU/L; group II, 1.9-10.6 mU/L). Mean peak TSH levels were significantly different in the two groups (group I, 24 +/- 7.7 mU/L; group II, 60.3 +/- 26.1 mU/L; P < 0.001). During long term follow-up, all 25 group I infants available for evaluation have been confirmed as clinically and biochemically normal. No infant diagnosed as normal was later found to have evidence of hypothyroidism. Fourteen infants in group II have had evidence of thyroid dysfunction. We conclude that the TSH response to TRH stimulation is a useful tool for the evaluation of infants suspected of having primary hypothyroidism. Whether hyperresponsiveness to TRH represents a form of neonatal hypothyroidism requiring treatment remains to be determined.

Osteoporosis: an unusual presentation of childhood Crohn's disease.

Osteoporosis is known to be associated with Crohn's disease. We report a 12-yr-old boy without a history of steroid use, in whom severe osteoporosis and multiple collapsed vertebrae were the presenting manifestations of Crohn's disease. After treatment of the Crohn's disease, he resumed normal growth and progressed through puberty. Concomitantly, he demonstrated a substantial recovery of vertebral bone mineral density and structure. Possible pathophysiological mechanisms underlying the osteoporosis and the subsequent improvement in bone density are discussed.

Prepubertal girls with premature adrenarche have greater bone mineral content and density than controls.

Body composition in premature adrenarche (PA) has not been described. We hypothesized that the increased adrenal androgens in PA would have a trophic effect on lean body components. We studied 14 PA subjects and 16 controls, all prepubertal Hispanic girls. The body composition parameters tested included height, weight, bone mineral density (BMD), bone mineral content (BMC), nonbone fat-free mass, total body potassium, total body water, and extracellular water. Bone age was determined in all PA subjects. Compared with controls, PA subjects had significantly higher BMC (P = 0.02) and BMD (P = 0.03) when adjusted for age, weight, height, and fat mass, but were not different in the following lean body components: fat-free mass, total body potassium, total body water, and extracellular water. There was no difference in BMD or BMC between the PA subjects with and without advanced bone age. These data suggest a specific effect of PA on bone mineral, but not on other lean body components. The absence of a correlation between bone age and bone mineral in this small group leads us to propose there are separate promoters of bone age advancement and bone mineral accrual. Candidate hormones for these processes include adrenal androgens, E, and IGF-I. The findings of this study suggest that hormonal alterations associated with PA affect bone mineral accrual and may elucidate the mechanisms involved in this process.

Effect of puberty on the relationship between circulating leptin and body composition.

Circulating concentrations of leptin are better correlated with absolute amounts of adipose tissue [fat mass (FM)] than with relative body fatness (body mass index or percent body fat). There is a clear sexual dimorphism in circulating concentrations of leptin (females > males) at birth and in adulthood. However, whether such dimorphism is present in the interval between these periods of development remains controversial. We examined body composition and clinical (Tanner stage) and endocrine (pituitary-gonadal axis hormones) aspects of sexual maturation in relationship to circulating concentrations of leptin in 102 children (53 males and 49 females, 6-19 yr of age) to evaluate the relationship between circulating leptin concentrations and body composition before and during puberty. Pubertal stage was assigned by physical examination (Tanner staging) and also assessed by measurement of plasma estradiol, testosterone, and pituitary gonadotropins. Body composition was determined by dual-energy x-ray absorptiometry and by anthropometry. Circulating concentrations of leptin in the postabsorptive state were determined by a solid-phase sandwich enzyme immunoassay. The effect of gender on the relationship between circulating leptin concentrations and FM was determined by ANOVA at each Tanner stage. Stepwise multiple linear regression analyses, including circulating concentrations of pituitary-gonadal axis hormones, and FM were performed, by gender, to determine whether the relationship between circulating concentrations of leptin and FM changes during puberty. Plasma leptin concentrations were significantly correlated with FM at all Tanner stages in males and females. Plasma leptin concentrations, normalized to FM, were significantly higher in females than males at Tanner stages IV and V but not at earlier stages of pubertal development. Plasma leptin concentrations, normalized to FM, were significantly greater in females at Tanner stage V compared with females at Tanner stage I and significantly lower in males at Tanner stage IV and V compared with males at Tanner stage I. These significant gender and maturational differences were confirmed by demonstrating that the regression equation relating circulating leptin concentrations to FM in females and males at Tanner stages IV and V were significantly different (predicted lower leptin concentrations in males than females with identical body composition) and that the regression equations relating circulating concentrations of leptin to FM in each gender before puberty (Tanner stage I) were significantly different (predicted higher plasma concentrations of leptin in prepubertal males and lower leptin concentrations in prepubertal females) than the same regression equations in later puberty. Circulating concentrations of testosterone were significant negative correlates of circulating concentrations of leptin normalized to FM in males when considered as a group over all pubertal stages. The inclusion in multivariate regression analyses of circulating concentrations of testosterone and estradiol, FM, fat-free mass, and gender did not eliminate a significant gender-effect (P < 0.05) on circulating concentrations of leptin at Tanner stages IV and V. The circulating concentration of leptin, normalized to FM, declines significantly in males and rises significantly in females late in puberty to produce a late-pubertal/adult sexual dimorphism. These studies confirm a potent role for gonadal steroids as mediators of this sexual dimorphism in circulating concentrations of leptin. (ABSTRACT TRUNCATED)

46,XX pure gonadal dysgenesis with growth hormone deficiency and impaired 3 beta-hydroxysteroid dehydrogenase activity.

Patients with 46,XX pure gonadal dysgenesis generally are of normal stature and have less than usual amounts of pubic and axillary hair. We report on a patient who presented at age 11.9 years with short stature, absence of breast development, and excessive pubic hair. Her karyotype in leukocytes, fibroblasts, and streak gonad was 46,XX. The patient was diagnosed as having growth hormone deficiency. Elevated ACTH stimulated levels of 17-hydroxypregnenolone and dehydroepiandrosterone and elevated ACTH stimulated ratio of 17-hydroxypregnenolone to 17-hydroxyprogesterone suggested inadequate adrenal 3 beta-hydroxysteroid dehydrogenase activity. Treatment with growth hormone resulted in improvement in growth velocity and replacement with estrogen in feminization. We suggest that the finding of short stature in patients with 46,XX pure gonadal dysgenesis should not be attributed to the syndrome, but rather requires investigation for possible growth hormone deficiency. The poor growth of our patient prior to growth hormone replacement implies that dehydroepiandrosterone, unlike testosterone and estrogen, is ineffective in promoting linear growth in the absence of adequate growth hormone.

Familial Pallister-Hall syndrome: case report and hormonal evaluation.

Pallister-Hall syndrome is a usually lethal dysplasia/malformation syndrome characterized by hypothalamic hamartoblastoma, hypopituitarism, postaxial polydactyly, craniofacial malformations, imperforate anus, and other malformations. We report a familial case in a male infant and his female sib fetus, suggesting autosomal recessive inheritance, or germinal mosaicism for an autosomal dominant mutation, or a segregating submicroscopic chromosome abnormality. Detailed endocrine evaluation on the surviving infant revealed documented pituitary function, pituitary deficit, and hypothalamic deficiency. We suggest that hypothalamic dysfunction contributes to the hypopituitarism seen in Pallister-Hall syndrome.

Body composition changes during Tanner stage 5.

Clinicians use the combination of Tanner stage 5 (T5) of puberty, final height, and epiphyseal fusion to define maturity. We tested the hypothesis that changes in body composition related to age are identifiable during T5. Asian, Black, Hispanic, and White T5 adolescents (n = 148, 72 females) had measurements taken of their height, weight, total body potassium by 40K counting, total body water by D2O dilution; and total body bone mineral, fat-free mass, and fat mass by dual-energy X-ray absorptiometry. The relative increases with age in lean body components were greater than those in height and weight, and were greater in males. Age was a significant determinant of all body components in males, but of only bone mineral in females. The effect of age was independent of ethnicity. These findings suggest an independent effect of age on body composition during T5, especially in males. We propose that peak levels of lean body components should be included in the definition of maturity in certain clinical and metabolic situations.

Very low-density lipoprotein metabolism in an unusual case of lipoatrophic diabetes.

Complete acquired lipoatrophic diabetes (LD) is characterized by nonketotic insulin-resistant diabetes, elevated very low-density lipoprotein (VLDL) triglyceride (TG) levels, and absent subcutaneous fat. We studied a young child in whom LD atypically developed after the onset of type 1 diabetes mellitus. On uncontrolled home diet the patient had triglyceride levels over 1,000 mg/dL on multiple occasions. In order to demonstrate the effects of caloric and dietary-fat restriction on VLDL metabolism, 3H-glycerol and autologous 125I-VLDL were used to quantitate the turnover of VLDL-TG and VLDL-apolipoprotein B (apo B) during two periods of caloric restriction. Consumption of a 900-kcal 40-g fat diet resulted in a plasma triglyceride level of 1383 mg/dL (ten-fold elevation). This hypertriglyceridemia was associated with markedly increased production rates of both VLDL-TG (73.7 mg/kg/h) and VLDL-apo B (126.9 mg/kg/d). Consumption of a 900-kcal 25-g fat diet resulted in a plasma TG level of 663 mg/dL. This reduction in plasma TG was associated with a 40% decrease in VLDL-TG production rate (PR) (45.1 mg/kg/h). There was no change in the production rate (PR) of VLDL-apo B. The hypertriglyceridemia in this patient was due to marked over production of VLDL. Furthermore, the studies demonstrate: (1) the independent benefits of caloric and dietary-fat restriction in the treatment of LD, and (2) that fat restriction lowered plasma triglyceride by its effect on the VLDL-TG production rate.

Body composition in prepubertal children with human immunodeficiency virus type 1 infection.

OBJECTIVE: To characterize the body composition of human immunodeficiency virus (HIV)-infected children, especially those with growth failure (GF), using laboratory-based methods. DESIGN: A cross-sectional study of body composition measurements. SETTING: Urban, hospital-based body composition laboratory. PARTICIPANTS: Thirty-four prepubertal children with HIV infection, aged 4 to 11 years, recruited from a pediatric HIV clinic. Eighteen HIV-infected children with GF, 16 HIV-infected children with normal rates of growth, and 52 healthy children were studied. MAIN OUTCOME MEASUREMENTS: Anthropometrics, body cell mass (BCM) by total body potassium counting, body fat percent, fat mass, and fat-free mass (FFM) by dual-energy x-ray absorptiometry were determined. RESULTS: Both groups of boys with HIV infection had significantly lower FFM/height ratios compared with healthy boys. The mean BCM/height ratio was also lower in HIV-infected boys with GF compared with healthy boys. Measures of fat of the HIV-infected boys with GF did not differ from healthy controls, but a statistical trend suggesting decreased body fat percent and fat mass/height ratio was observed in HIV-infected boys without GF (P=.06 and .07, respectively). Mean height-for-age, weight-for-age, and weight-for-height percentiles were significantly decreased in HIV-infected boys regardless of growth status as compared with healthy boys. The mean FFM/ height and BCM/height ratios were decreased in HIV-infected girls with GF compared with healthy girls. Body fat percentage and fat mass/height ratio did not differ among the 3 groups of girls. The mean weight-for-height percentiles were not different among the 3 groups of girls. The HIV-infected girls with GF had significantly lower mean height-for-age and weight-for-age percentiles than HIV-infected girls without GF and healthy girls. The mean height-for-age percentiles of the HIV-infected girls with GF did not differ from the healthy girls. CONCLUSIONS: Boys and girls with HIV-associated GF had diminished FFM and BCM. The decrease in FFM and BCM was in striking contrast to the fat compartment, which was normal. Decreased FFM was also detected in boys with HIV infection and normal growth but not in girls with HIV infection and normal growth, suggesting that HIV infection may affect boys differently than girls. The preferential decrease in FFM and BCM over fat observed in these children is similar to findings reported in adults with acquired immunodeficiency syndrome wasting.

Dual-energy X-ray absorptiometry: analysis of pediatric fat estimate errors due to tissue hydration effects.

Dual-energy X-ray absorptiometry (DXA) percent (%) fat estimates may be inaccurate in young children, who typically have high tissue hydration levels. This study was designed to provide a comprehensive analysis of pediatric tissue hydration effects on DXA %fat estimates. Phase 1 was experimental and included three in vitro studies to establish the physical basis of DXA %fat-estimation models. Phase 2 extended phase 1 models and consisted of theoretical calculations to estimate the %fat errors emanating from previously reported pediatric hydration effects. Phase 1 experiments supported the two-compartment DXA soft tissue model and established that pixel ratio of low to high energy (R values) are a predictable function of tissue elemental content. In phase 2, modeling of reference body composition values from birth to age 120 mo revealed that %fat errors will arise if a "constant" adult lean soft tissue R value is applied to the pediatric population; the maximum %fat error, approximately 0.8%, would be present at birth. High tissue hydration, as observed in infants and young children, leads to errors in DXA %fat estimates. The magnitude of these errors based on theoretical calculations is small and may not be of clinical or research significance.

Body composition in children and adults by air displacement plethysmography.

OBJECTIVES: Air displacement plethysmography (ADP) may provide a partial alternative to body density (Bd) and therefore body composition measurement compared to conventional hydrodensitometry (Hd) in children. As there are no evaluation studies of ADP in children, this study had a two-fold objective: to compare Bd estimates by ADP and Hd; and to compare fat estimates by both ADP and Hd to fat estimates by another reference method, dual energy X-ray absorptiometry (DXA). SETTING: Obesity Research Center, St. Luke's/Roosevelt Hospital, New York, USA. SUBJECTS: One hundred and twenty subjects (66 females/54 males) who ranged in age from 6-86 y and in body mass index (BMI, kg/m2) from 14.1-40.0 kg/m2 met study entry criteria. STUDY DESIGN: Cross-sectional study of healthy children (age < or = 19 y) and adult group for comparison to earlier studies. Each subject completed ADP, Hd, and DXA studies on the same day. Only subjects with subjectively-judged successful Hd studies were entered into the study cohort. RESULTS: There was a high correlation between Bd by ADP and Hd (Bd Hd = 0.11 + 0.896 x Bd ADP; r = 0.93, SEE = 0.008 g/cm3, P < 0.0001), although the regression line slope and intercept differed significantly from 1 and 0, respectively. Additional analyses localized a small-magnitude Bd bias in the child (n = 48) subgroup. Both ADP and Hd %fat estimates were highly correlated (r > 0.9, P < 0.0001) with %fat by DXA in child and adult subgroups. Bland-Altman analyses revealed no significant %fat bias by either ADP or Hd vs DXA in either children or adults, although a bias trend (P = 0.11) was detected in the child subgroup. CONCLUSION: With additional refinements, the air displacement plethysmography system has the potential of providing an accurate and practical method of quantifying body fat in children as it now does in adults.

Pencil-beam versus fan-beam dual-energy X-ray absorptiometry comparisons across four systems: appendicular lean soft tissue.

Dual-energy X-ray absorptiometry (DXA) provides an important opportunity for estimating total body skeletal muscle (SM) mass from DXA-measured appendicular lean soft tissue (ALST). A DXA SM prediction model was developed with magnetic resonance imaging as the reference and ALST (i. e., sum of arm plus leg lean soft tissue) as a main predictor variable. In the present study we examined whether ALST estimates are comparable across systems (i. e., penciland fan-beam) and manufacturers. Pencil-beam systems (Lunar DPX and DPX-L) are usually considered more accurate but slower than fan-beam systems (Lunar Prodigy and Hologic Delphi A). In this study we compared ALST estimates in 35 healthy adults across these four systems. The methods gave similar group mean (+/-SD) values and were highly intercorrelated. There was no significant bias detected across the four systems. ALST estimates from the evaluated DXA systems are comparable and thus appear interchangeable as methods for quantifying total body SM in vivo.

Dual X-Ray absorptiometry in pediatric studies: changing scan modes alters bone and body composition measurements.

The use of dual X-ray absorptiometry (DXA) for measurement of bone mineral and body composition in pediatric subjects faces a major technical issue: body size dictates choice of scan mode. However, different scan modes change results in the same subject, thus affecting the accuracy of bone/body composition measurements and especially the capacity to measure changes owing to either growth or intervention. To evaluate the effect of scan mode selections on measurements of bone mineral and body composition, 13 children with weights at the cutoff point between the pediatric large and adult medium scan modes of Lunar DPX or DPXL (Lunar, Madison, WI) with software 3.6 g (35.3 +/- 0.9 kg or 77.7 +/- 2.0 lb) were scanned by both modes. Adult medium mode gave significantly higher results than pediatric large mode for total body fat mass (11.1%), fat% (10.5%), bone mineral content (8.1%), and bone area (1.3%) (p < 0.02). The differences between pediatric large and adult medium modes in fat measurements increased with increasing body mass index ([BMI], kg/m(2)), body surface area ([BSA], m(2)), and trunk size (mm), whereas the differences in bone mineral measurement tended to be greater only with increasing BMI and BSA. None of the differences were correlated to body weight. This study suggests that scan mode selections based on trunk size, BMI, or BSA instead of body weight may improve continuity of bone and body composition measurements by the DXA technique in pediatric subjects.

Correlations between skeletal muscle mass and bone mass in children 6-18 years: influences of sex, ethnicity, and pubertal status.

A constant sex-specific relationship between skeletal muscle mass and bone mass was observed in healthy adults based on TBK/TBCa, using TBK (total body potassium) by 40K counting and TBCa (total body calcium) by in-vivo neutron activation analysis (Ellis and Cohn, 1975). We revisited this topic in children by studying correlations between TBK and TBCa, and by comparing TBK/TBCa between sexes, pubertal groups (prepubertal and pubertal) and ethnic groups in 141 white, 101 black, and 62 Asian healthy children, aged 6 - 18 years, living in New York City. TBK was measured by 40K counting, and TBCa by dual energy x-ray absorptiometry. TBK and TBCa were significantly correlated from 6 to 18 years (r > 0.93), but the correlation equations varied by gender and ethnicity. Boys had significantly more TBK and greater TBK/TBCa than girls at a given age and weight, reflecting greater skeletal muscle mass in boys from 6 years, the age at which the study started. TBK/TBCa in blacks was significantly smaller than whites and Asians in both sexes in prepuberty and puberty, and pubertal black girls had the smallest mean TBK/TBCa. No significant differences were found between whites and Asians. TBK/TBCa decreased as body weight increased in prepubertal girls, and decreased as body weight and age increased in pubertal girls, but did not change with body weight or age in boys of any subgroup. The inverse relationship between TBK/TBCa and age in pubertal girls suggests greater increase in TBCa compared to TBK than in other groups, while the constant TBK/TBCa in boys reflects proportional increases in TBK and TBCa. Thus TBK/TBCa can be used as an index of relative growth in skeletal muscle mass and bone mass in white, black, and Asian children according to sex, age and pubertal status.

Mandating private pensions: experience in four European countries.

This study examines the experience of four countries--the Netherlands, Sweden, Switzerland, and the United Kingdom--in which the mandating of private pensions exists or has been considered. Proposals to mandate private pensions in the United States have been introduced in Congress several times. The analysis of foreign thinking presented here provides a background on the reasoning behind such a policy and on the integration of private and public systems and the problems involved. A prime reason for mandating private pensions--instead of seeking higher social security benefits or additional social security layers--has been the pressure to avoid higher payroll taxes. Some countries already had such high contribution rates that they sought other means to improve benefits. Adding a layer of private pensions, it was thought, does not involve Government mechanisms and keeps the money in the private sector. Yet mandating by law creates many problems, and no country has fully implemented such legislation.

The relationships between public and private pension schemes: an introductory overview.

Only recently have social insurance and private pensions, collectively, come to be thought of in terms of a total social security benefit package. The economic problems brought on by the 1974 oil crisis initially triggered consideration of a common, integrated role for the two systems. The second oil crisis reinforced the relative expansion in private pension programs, as a supplement to social security. Before these events, private and public pension programs interacted in only a limited number of ways, confined to relatively few countries. These interactions were largely confined to collective bargaining, whereby private pensions were gradually extended to nearly all employees in France and Sweden; mandating, or legally requiring private supplementation of social security, debated in several countries in the early 1970's, but postponed by the 1974 oil crisis; and contracting out, or covering a part of the social security benefit under a private plan, as in the United Kingdom. Overall, the tradition of private pensions was not very strong or broadbased. The current debate centers on which public/private pension mix is desirable from the point of view of an old-age income-maintenance program. A new element is the rising support for a "third pillar"--individual tax-encouraged savings--not only as a supplement, but as an alternative to social insurance.