Comparison of percent body fat estimates using air displacement plethysmography and hydrodensitometry in adults and children.

PURPOSE: The purpose of the study was to compare estimates of body density and percentage body fat from air displacement plethysmography (ADP) to those from hydrodensitometry (HD) in adults and children and to provide a review of similar recent studies. METHODS: Body density and percentage body fat (% BF) were assessed by ADP and HD on the same day in 87 adults aged 18-69 y (41 males and 46 females) and 39 children aged 8-17 y (19 males and 20 females). Differences between measured and predicted thoracic gas volumes determined during the ADP procedure and the resultant effects of those differences on body composition estimates were also compared. In a subset of 50 individuals (31 adults and 19 children), reliability of ADP was measured and the relative ease or difficulty of ADP and HD were probed with a questionnaire. RESULTS: The coefficient of reliability between %BF on day 1 and day 2 was 96.4 in adults and 90.1 in children, and the technical error of measurement of 1.6% in adults and 1.8% in children. Using a predicted rather than a measured thoracic gas volume did not significantly affect percentage body fat estimates in adults, but resulted in overestimates of percentage body fat in children. Mean percentage body fat from ADP was higher than percentage body fat from HD, although this was statistically significant only in adults (29.3 vs 27.7%, P<0.05). The 95% confidence interval of the between-method differences for all subjects was -7 to +9% body fat, and the root mean square error (r.m.s.e.) was approximately 4% body fat. In the subset of individuals who were asked to compare the two methods, 46 out of 50 (92%) indicated that they preferred the ADP to HD. CONCLUSION: ADP is a reliable method of measuring body composition that subjects found preferable to underwater weighing. However, as shown here and in most other studies, there are differences in percentage body fat estimates assessed by the two methods, perhaps related to body size, age or other factors, that are sufficient to preclude ADP from being used interchangeably with underwater weighing on an individual basis.

Sex differences in bone mass acquisition during growth: the Fels Longitudinal Study.

Risk of osteoporosis in later life may be determined during adolescence and young adulthood. The present study used longitudinal data to examine the accumulation of bone mineral content (BMC) and bone mineral density (BMD) in Caucasian subjects ages 6-36 yr. Growth in BMC and BMD (measured by dual X-ray absorptiometry; Lunar, Madison, WI) of 94 males and 92 females was monitored for a mean period of 4.29 yr. The main findings were that there were no sex differences in BMC or BMD during the prepubertal stage; however, females had significantly higher BMD of the pelvis and BMC and BMD of the spine during puberty, and postpubertal males generally had significantly higher BMC and BMD than their female counterparts. In addition, the longitudinal rate of bone accumulation in both sexes increased rapidly during childhood and adolescence and was nearly complete at the end of puberty. Finally, peak BMC and BMD was achieved between the ages of 20 and 25 and occurred earlier in females than in males. The rates of growth and timing of peak bone mass as reported here define the crucial period during which intervention protocols should be developed for maximizing skeletal mass to prevent the development of osteoporosis.

Childhood body composition in relation to body mass index.

OBJECTIVE: The aim is to describe body composition in relation to body mass index (BMI; body weight/stature(2)) to provide health care professionals insight into the meaning, significance, and limitations of BMI as an index of adiposity during childhood. METHODS: Data from 387 healthy, white children 8 to 18 years of age from the Fels Longitudinal Study were analyzed. Measurements were scheduled annually and each child was examined 1 to 11 times, totaling 1748 observations. Total body fat (TBF) and fat-free mass (FFM) were determined from hydrodensitometry. Stature and weight were measured using standard methods and BMI and the components of BMI, TBF/stature(2), and FFM/stature(2) were calculated. Analyses included correlations between BMI and body composition variables; age-related patterns of BMI, TBF/stature(2), and FFM/stature(2); and annual changes in BMI, TBF/stature(2), and FFM/stature(2). RESULTS: Generally, correlations between BMI and body composition variables were strong and significantly different from zero. Means for BMI throughout childhood were similar for boys and girls, although significantly larger values were observed for girls at ages 12 to 13 years. Age-related patterns of TBF/stature(2) and FFM/stature(2) differed between sexes. In each sex, annual increases in BMI were driven primarily by increases in FFM/stature(2) until late adolescence, with increases in TBF/stature(2) contributing to a larger proportion of the BMI increases in girls than in boys. CONCLUSIONS: Unlike adults, annual increases in BMI during childhood are generally attributed to the lean rather than to the fat component of BMI. Because the properties of BMI vary during childhood, health care professionals must consider factors such as age and sex when interpreting BMI.

CDC growth charts: United States.

OBJECTIVES: This report presents the revised growth charts for the United States. It summarizes the history of the 1977 National Center for Health Statistics (NCHS) growth charts, reasons for the revision, data sources and statistical procedures used, and major features of the revised charts. METHODS: Data from five national health examination surveys collected from 1963 to 1994 and five supplementary data sources were combined to establish an analytic growth chart data set. A variety of statistical procedures were used to produce smoothed percentile curves for infants (from birth to 36 months) and older children (from 2 to 20 years), using a two-stage approach. Initial curve smoothing for selected major percentiles was accomplished with various parametric and nonparametric procedures. In the second stage, a normalization procedure was used to generate z-scores that closely match the smoothed percentile curves. RESULTS: The 14 NCHS growth charts were revised and new body mass index-for-age (BMI-for-age) charts were created for boys and girls (http://www.cdc.gov/growthcharts). The growth percentile curves for infants and children are based primarily on national survey data. Use of national data ensures a smooth transition from the charts for infants to those for older children. These data better represent the racial/ethnic diversity and the size and growth patterns of combined breast- and formula-fed infants in the United States. New features include addition of the 3rd and 97th percentiles for all charts and extension of all charts for children and adolescents to age 20 years. CONCLUSION: Created with improved data and statistical curve smoothing procedures, the United States growth charts represent an enhanced instrument to evaluate the size and growth of infants and children.

Total-body and regional bone mineral content and areal bone mineral density in children aged 8-18 y: the Fels Longitudinal Study.

BACKGROUND: Techniques for cross-calibration of bone mineral content (BMC) and bone mineral density (BMD) between manufacturers of dual-energy X-ray absorptiometry (DXA) instruments are currently inadequate for total body measurements. Therefore, manufacturer-specific data for BMC and BMD in children are needed. OBJECTIVE: We provided age- and sex-specific means and SDs for total-body and regional BMC and areal BMD in 8-18-y-old white children. DESIGN: BMC and BMD of the head, arms, legs, pelvis, spine, and total body were determined by DXA. Data include 465 annual measurements from 148 healthy children with body weights between 30 and 100 kg and statures <190 cm. RESULTS: There were significant sex differences in BMC at ages 15-18 y for the total body and legs, at ages 12 and 15-18 y for arms and pelvis, at ages 11-13 and 16-18 y for the spine, and at ages 10-11 y for the head. There were significant sex differences in BMD at ages 16-18 y for total body, arms, and legs; at ages 12-13 and 16-18 y for the pelvis; at ages 12-14 and 18 y for the spine; and at ages 13-18 y for the head. CONCLUSIONS: Data presented in this investigation can be used to compare the BMC and BMD of 8-18-y-old white children (with statures <190 cm and body weights between 30 and 100 kg) using DXA.

Serial changes in body composition throughout adulthood and their relationships to changes in lipid and lipoprotein levels. The Fels Longitudinal Study.

Few studies have examined the relationships between measures of body composition and lipid and lipoprotein levels in long-term serial data from individuals unselected for cardiovascular disease- or obesity-related variables, and none have considered such extensive serial data as used in the current study. The aim was to examine in such individuals the associations between annual changes in lipid and lipoprotein levels and concurrent changes in total body fat, fat-free mass, percent body fat, and body mass index. Serial data from 1304 examinations of 423 adult white participants in the Fels Longitudinal Study were analyzed sex-specifically in 2 age groups, 18 through 44 years and 45 to 65 years. A regressive analytic approach utilized the long-term (4 to 20 years) serial data of individuals. Annual changes in adiposity, independent of levels of lean tissue changes, before and after age 45 for men and women were significantly correlated with corresponding annual changes in cholesterol and low density lipoprotein cholesterol. In men before age 45, changes in triglycerides and high density lipoprotein cholesterol were also significantly associated with changes in adiposity, with the relationship remaining after age 45 in high density lipoprotein cholesterol. Increases in adiposity in individuals are associated with changes in lipid and lipoprotein levels in the direction of increased risk for cardiovascular disease. Adult levels of total cholesterol and low density lipoprotein cholesterol across age and sex and high density lipoprotein cholesterol in men are responsive to changes in adiposity, independent of initial adiposity or lipid and lipoprotein levels.

Age- and maturity-related changes in body composition during adolescence into adulthood: the Fels longitudinal study.

We examined patterns of change in body composition from 8 to 20 yrs of age and the effects of rate of maturation on these patterns using serial data for total body fat (TBF). There is a continual increase, but a declining rate of change with age in TBF. For %BF the same pattern as for TBF exists for females, but for males the pattern of change in percentage body fat (%BF) reflects the concurrent changes in fat free mass (FFM). For FFM, there is an increase in females that slows at older ages, but in males there is a continual rapid increase until young adulthood. There is marked tracking for body composition persisting from childhood to adulthood. At the same age, rapidly maturing children have significantly larger TBF, %BF and FFM than slowly maturing children.

Adult changes in body composition are associated with changes in cholesterol levels: the Fels longitudinal study.

Serial data from 507 adult participants in the Fels Longitudinal Study were used to study relationships between average annual changes in serum cholesterol levels and annual changes in total body fat, fat-free mass, percent body fat or body mass index in men and women aged 18-45 years or 45-65 years. Average annual changes in adiposity before and after 45 years of age for men and women show statistically significant, strong, positive relationships with corresponding changes in cholesterol levels.

Opportunities and difficulties in long-term studies of growth.

Overviews are presented of the University of Melbourne Child Growth Study and of the Fels Longitudinal Study; each of these studies had a major focus on the growth and maturation of children. Planning, study design, logistics and staffing varied between these studies, but each led to exciting research opportunities that can exist only when longitudinal data are available. There are important differences between these studies in the types of participants, ages at examinations, the variables measured, some topics of central concern, and in funding. In each study, research productivity was low in the early years, the retention of participants was a major concern, and it was necessary to maintain a balance between data collection, data management, and data analysis. More such studies are needed that focus on particular population groups and topic areas and that utilize the lessons of the past to maximize the chances of future success.

Growth in weight, recumbent length, and head circumference for preterm low-birthweight infants during the first three years of life using gestation-adjusted ages.

Data from 867 preterm low-birthweight participants in the Infant Health and Development Program (IHDP) were used to develop reference data for growth status at an age and for increments from term to 36 month gestation-adjusted age (GAA). Weight, length and head circumference were recorded at 4 month intervals in the first year and at 6 month intervals in the second and third years. Selected percentiles for values at an age (status values) and increments for age intervals are presented in graphs separately for VLBW infants (< or = 1500 g at birth) and for LBW infants (1501-2500 g at birth). Percentiles of weight increments are presented beginning shortly before term for 1 month intervals to 6 month GAA, for 2 month intervals to 12 month GAA, and for 3-month intervals to 36 month GAA. Percentiles for length and head circumference increments are presented from term to 6 months for 2-month intervals, and to 36 month GAA for 3 month intervals. Among LBW infants, boys, had larger status and increment values than girls (P < 0.05), but there were no significant sex-associated differences in VLBW infants for status or increments. The mean status values and increments in weight and head circumference of the LBW infants were larger than those of VLBW infants, but the differences in length were not significant.

Reference data for head circumference-for-length in preterm low-birth-weight infants.

OBJECTIVE: To provide reference data for head circumference-for-length in preterm low-birth-weight infants that are independent of age, but extend for the ranges of head circumference (34-49 cm) and length (52.0-102.9 cm) values found from birth to 36 months of gestation-adjusted age. DESIGN: Measurements were made at 9 ages in 867 preterm infants in the Infant Health Development Program, a randomized clinical trial that included various ethnic groups at 8 sites. At birth, two thirds of the infants weighed less than 2000 g, and one third weighed between 2000 and 2500 g. Measurements were taken at birth, at 40 weeks of postconceptional age, and at 4, 8, 12, 18, 24, 30, and 36 months of gestation-adjusted age. A model fitted to the serial data for each infant was used to estimate head circumference and length from 36 weeks after conception to 36 months of gestation-adjusted age. RESULTS: Tables and charts of means and SDs and selected percentiles for each sex were made. These tables and charts are for very low (< or = 1500 g) and low-birth-weight (1501-2500 g) infants by 3-cm intervals of length. CONCLUSION: These tables and charts should assist clinicians in evaluating and monitoring head circumference in preterm low-birth-weight infants by taking body length into account.

Age- and maturity-related changes in body composition during adolescence into adulthood: the Fels Longitudinal Study.

OBJECTIVES: To examine patterns of change in total body fat (TBF), percent body fat (%BF), and fat-free mass (FFM), from 8-20 y of age and the effect of rate of skeletal maturation. To determine the degree of tracking of body composition for individuals from childhood into adulthood. RESEARCH DESIGN: Annual serial data for TBF, %BF and FFM from underwater weighing using a multicomponent body composition model were collected from 130 Caucasian males and 114 Caucasian females between 1976 and 1996. Rate of maturation was defined as FELS skeletal age (SA) less chronological age (CA). Random effects models were used to evaluate general patterns of change and tracking of individual serial data over the 12 y age range. RESULTS: Changes in TBF followed a quadratic model for males and for females with declining rates of change. Changes for %BF followed a cubic model for males and females. General patterns of change for FFM followed a cubic model for males and a quadratic model for females. TBF for males and females increased with age, but the rates of change declined with age. %BF for females increased from age 8-20 y. For males, %BF increased with age, but the positive rates of change declined and became a negative when aged about 13 y and reached a minimum at about the age of 15 y. The rate of change for %BF increased thereafter. FFM for males and females increased with age, but the rates of change decreased with age. The extent of tracking is inversely related to the length of the time interval. At the same age, rapidly-maturing children have significantly larger amounts of TBF, %BF and FFM then slow-maturing children. Tracking in body composition for individuals persisted from childhood to adulthood. CONCLUSIONS: (1) There are gender-associated differences in these patterns of change for %BF and FFM but not for TBF; (2) TBF, %BF and FFM increased with increased rates of maturation; (3) significant tracking in body composition for individuals persists from childhood to adulthood.

Weight-for-length reference data for preterm, low-birth-weight infants.

OBJECTIVE: To provide weight-for-length reference data for preterm, very-low-birth-weight and low-birth-weight infants. DESIGN: Data from 867 infants (428 boys and 439 girls) in the Infant Health and Development Program, who each were preterm and who had a low birth weight, were used to develop weight-for-length reference data. The Infant Health and Development Program is a national, randomized, clinical trial that included various ethnic groups at 8 sites. At each site, sampling ensured that two thirds of the infants in the study weighed 2000 g or less and that one third of the infants weighed from 2001 to 2500 g at birth. Infants were examined at birth, at 40 weeks' postconception, and at 4, 8, 12, 18, 24, 30, and 36 months' gestation-adjusted age. Gestation-adjusted age was used instead of chronological age from birth to correct for the degree of prematurity. RESULTS: Weight-for-length percentiles are given for lengths at 3-cm intervals ranging from 48 to 100 cm. These percentiles are sex specific and are for a very-low-birth-weight group (< or = 1500 g) and a low-birth-weight group (1501-2500 g). CONCLUSIONS: These data should assist screening for deviations from normal growth and may aid in the early detection of failure to thrive and excessive weight gain in infancy.

Skeletal age as a determinant of bone mass in preadolescent females.

OBJECTIVE: To evaluate the association between chronological age, skeletal age, pubertal stage, and basic anthropometry with bone mass of the total body, forearm, and second metacarpal bone in 456 healthy Caucasian females, aged 8-13 years. DESIGN: Total body and forearm bone measurements were performed by dual X-ray absorptiometry, while bone mass of the second metacarpal was assessed by radiogrammetry. Skeletal age (SA) was assessed by the FELS method and pubertal stage was self-determined by selecting corresponding illustrations of breast and public hair development. The Cp criterion was used to select the best multiple regression model containing the subset of independent variables with the least bias and best predictive ability for each of the measured bone mass variables. RESULTS: Of all the independent variables, weight, stature, and SA emerged as the most significant predictors for almost all the bone mass variables. Multiple regression models were created based on the Cp criterion with the resulting R2 (adjusted) for bone mineral content of total body, proximal forearm, ultradistal forearm, length of second metacarpal, as well as of total, medullary, and cortical areas: 0.793, 0.523, 0.390, 0.602, 0.232, 0.073, and 0.264, respectively. The measured bone variables were also regressed on SA using either quadratic or linear equations, depending on the shape of the cubic splines used for the best curve fitting. Significant positive association (p < 0.0001) of SA and each of the bone variables was noted, the highest being with bone mineral density and content of total body (R2 = 0.176, 0.338) and proximal and ultradistal forearm (R2 = 0.216, 0.203, 0.106, 0.201), respectively, as well as with the length of the second metacarpal bone (R2 = 0.339). Chronological age and pubertal stage did not have statistically significant predictive abilities for bone mass variables in the multiple regression models. CONCLUSIONS: We conclude that skeletal age is a powerful determinant of bone mass in children. It can be used as the criterion for the selection of a biologically homogeneous population with regard to bone mass. This may be important for the design of intervention studies targeting bone mass of children and adolescents.

Relationships between the Body Mass Index and body composition.

The aims of this study were to evaluate the Body Mass Index (BMI) (weight/stature2) as a proxy for percent body fat (%BF) and to determine its association with fat-free mass (FFM). Multivariate analysis of variance and partial correlations were used to examine relationships between BMI and %BF and FFM from densitometry for 504 men and 511 women, aged 20 to 45 years. Sensitivity/specificity analyses used cut offs of 28 kg/m2 in men and 26 kg/m2 in women for BMI, and 25% in men and 33% in women for %BF. Significantly higher associations existed in each gender between BMI and %BF in the upper BMI tertile than in the lower BMI tertiles. In the lower BMI tertiles, correlations between BMI and FFM were approximately twice as large as those between BMI and %BF. The BMI correctly identified about 44% of obese men, and 52% of obese women when obesity was determined from %BF. BMI is an uncertain diagnostic index of obesity. Results of Receiver Operator Characteristic (ROC) analyses using %BF and total body fat, both provided a BMI of 25 kg/m2 in men and 23 kg/m2 in women as diagnostic screening cut offs for obesity.

Growth outcome of "normal" short children who are retarded in skeletal maturation.

The growth and adult stature of "short normal slow maturing" children (SNSMC) have not been adequately studied. We applied a well-known adult stature prediction method to SNSMC and average children (AC). The accuracy of adult stature prediction in SNSMC warranted its use as a guide to the effectiveness of treatment (average median absolute errors: 1.71 cm males, 1.61 cm females). Additionally, we derived biological parameters from the serial statures for SNSMC and AC. Several of the biological parameters differed significantly between the SNSMC and AC in both sexes (stature velocity and age at onset of the pubescent spurt, age at peak height velocity, and the increment in stature from peak height velocity to 18 years) and the differences between these groups in stature at onset of the pubescent spurt and at peak height velocity were significant for males. The differences were not significant in either sex for the rate of growth at peak height velocity or the increase in stature from the onset of the pubescent spurt to peak height velocity.

Human body composition and the epidemiology of chronic disease.

Obesity and body fat distribution (FD) are established risk factors for chronic diseases. The body mass index (BMI) and the waist/hip circumference ratio (WHR) are used conventionally as indices of obesity and FD in epidemiological studies. Although some general limitations of these indices are recognized, others that affect their use in relative risks for disease are not well recognized. These include effects of sex, ethnicity, and especially age on the relationships between these indices and body composition, which can result in substantial misclassification of obesity and FD. There is considerable variability in body composition for any BMI, and some individuals with low BMIs have as much fat as those with high BMIs. This results in poor sensitivity for classifying levels of body fatness (e.g., too many "false negatives," or overweight individuals classified as not overweight), and relative risks are attenuated across all categories of BMI. A more serious problem, however, is that at different ages the same levels of BMI correspond to different amounts of fat and fat-free mass. Data from the Rosetta Study and the New Mexico Aging Process Study show that older adults have, on average, more fat than younger adults at any BMI, due to the loss of muscle mass with age. As a result, the sensitivity of BMI cutpoints with respect to body fatness decreases with age, and the use of a fixed cutpoint for all ages results in "differential misclassification bias." Taken together, these issues suggest that the increases with age in the prevalences of overweight and obesity, and in the risks for chronic diseases, may be mis-estimated using BMI. Similar issues may affect the use of WHR for estimating prevalences and associated risks of FD. New field methods for estimating body composition are available that can be applied in large, epidemiologic follow-up studies of chronic diseases. These methods will allow epidemiologists to consider, for example, whether it is increased fat, or the replacement of fat-free mass with fat, with age that is associated with risk for chronic disease.

The timing of sexual maturation in a group of US white youths.

The purpose of this study was to present US reference data for chronological ages at which stages of sexual maturation were observed in white youths. Recent serial data from 78 males and 67 females were analyzed to obtain descriptive statistics for the ages at onset of these stages and the mean ages at which the stages are observed. These reference data should assist the identification of white US youths who are maturing at rapid or slow rates and the interpretation of growth data.

Body composition of ethnic groups in the US.

Total body composition has not been reported from national samples of ethnic groups in the US but the data being recorded in the Third National Health and Nutrition Examination Survey include anthropometric variables and bioelectric impedance that jointly would allow the prediction of fat-free mass and other body composition variables for individuals. If these values were used in combination with the sample weighing coefficients, they could provide national estimates for composition values in whites. Afro-Americans and Hispanic-Americans. Despite the limitations of the reports currently available. data from relatively large groups will be summarised and ethnic comparisons will be made taking into account the procedures by which the data were obtained. Data for regional body composition. mainly skinfold thicknesses and circumferences, arc much more plentiful. They allow the evaluation of possible secular trends and of fat patterning within ethnic groups and the possible interplay of genetic and environmental influences.