Is sexual maturity occurring earlier among U.S. children?

PURPOSE: To compare the onset and completion of sexual maturation among U.S. children between 1966 and 1994. METHODS: Tanner stages were from 3042 non-Hispanic white boys, 478 black boys, 2625 white girls, and 505 black girls (NHES 1966-70), from 717 Mexican-American boys and 712 Mexican-American girls (HHANES 1982-84) and from 259 non-Hispanic white boys, 411 black boys, 291 white girls, 415 black girls, 576 Mexican-American boys and 512 Mexican-American girls (NHANES III 1988-1994). Proportions of entry into a stage, probit analysis estimated medians and selected percentiles for ages at entry were calculated using SUDAAN. RESULTS: NHANES III (1988-1994) non-Hispanic white boys entered stage 2, 3, and 4 genital development and stages 3 and 4 pubic hair earlier than NHES (1966-1970) white boys, but they entered stage 5 genital development significantly later. NHANES III (1988-1994) Mexican-American boys were in stage 2, 3 and 4 genital development earlier than HHANES (1982-1984) boys, but entry into stage 5 genital and pubic hair development was not significant. NHANES III (1988-1994) white girls entered stage 5 pubic hair later than NHES (1966-1970) white girls. NHANES III (1988-1994) Mexican-American girls entered stage 2 breast and pubic hair development earlier than HHANES (1982-1984) girls, entered stage 4 breast and pubic hair development earlier but entered stage 5 pubic hair later than the HHANES (1982-1984) girls. CONCLUSION: Persuasive evidence of a secular trend toward early maturation is not found between 1966 and 1994 in non-Hispanic black boys and non-Hispanic black and white girls. Some evidence of this trend is found in non-Hispanic white boys between 1966 and 1994 and in Mexican-American boys and girls between 1982 and 1994.

Heritability of age at menarche in girls from the Fels Longitudinal Study.

Menarche is the hallmark maturational event of female childhood. Many studies indicated a significant genetic contribution to the timing of the onset of menstruation, but most of these studies were limited by the use of retrospective data and by the use of data from only certain types of relatives (i.e., mothers and daughters, sisters, or twin sisters). The primary goal of this study was to use a modern maximum likelihood quantitative genetic method to estimate the heritability (h(2)) of age at menarche, using familial data collected over the course of the 74-year-old Fels Longitudinal Study. The secondary goal was to review earlier studies of the heritability of age at menarche. The study of the heritability of age at menarche presented here is unique for two reasons. First, because of the Fels Longitudinal Study's serial design, age-at-menarche data were collected prospectively from most participants. Second, because the Fels Longitudinal Study is a family study that has been conducted for decades, age-at-menarche data are available from many types of female relatives spanning multiple households and generations. The best-fitting and most parsimonious quantitative genetic model included provision for a secular decrease in age at menarche, and estimated the h(2) of age at menarche to be 0.49+/- 0.13 (95% confidence interval of h(2),=0.24-0.73). The results of this study are in general agreement with the findings of most previous studies of genetic influences on age at menarche, and suggest that it is reasonable to consider it well-established that approximately half the phenotypic variation among girls from developed nations in the timing of menarche is due to genetic factors.

Age at menarche and racial comparisons in US girls.

BACKGROUND: Concern regarding change in the onset of sexual maturation of US girls has increased the need for current information on age at menarche from a national sample. Previous reports have been sparse and interpretation has been limited because of the racial composition and ages of the samples. OBJECTIVE: The objectives of this study were to estimate the distribution of age at menarche for all US girls and for non-Hispanic white, black, and Mexican American girls in the Third National Health and Nutrition Examination Survey and to test for racial differences. DESIGN: Menstrual status data were collected from 2510 girls aged 8.0 to 20.0 years. The Third National Health and Nutrition Examination Survey followed a complex, stratified, multistage probability cluster design. SUDAAN was used to calculate proportions of girls reaching menarche at an age. Ages at menarche were estimated by probit analysis at the ages at which 10%, 25%, 50%, 75%, and 90% of the girls attained menarche. RESULTS: Less than 10% of US girls start to menstruate before 11 years, and 90% of all US girls are menstruating by 13.75 years of age, with a median age of 12.43 years. This age at menarche is not significantly different (0.34 years earlier) than that reported for US girls in 1973. Age at menarche for non-Hispanic black girls was significantly earlier than that of white girls at 10%, 25%, and 50% of those who had attained menarche, whereas Mexican American girls were only significantly earlier than the white girls at 25%. CONCLUSION: Overall, US girls are not gaining reproductive potential earlier than in the past. The age at menarche of non-Hispanic black girls is significantly earlier than that of non-Hispanic white and Mexican American girls.

National estimates of the timing of sexual maturation and racial differences among US children.

OBJECTIVE: To provide clinically meaningful, normative reference data that describe the timing of sexual maturity indicators among a national sample of US children and to determine the degree of racial/ethnic differences in these estimates for each maturity indicator. METHODS: Tanner staging assessment of sexual maturity indicators was recorded from 4263 non-Hispanic white, black, and Mexican American girls and boys aged 8.00 to 19.00 years as part of the Third National Health and Nutrition Examination Survey (NHANES III) conducted between 1988 and 1994. NHANES III followed a complex, stratified, multistage probability cluster design. SUDAAN was used to calculate the mean age and standard error for each maturity stage and the proportion of entry into a maturity stage and to incorporate the sampling weight and design effects of the NHANES III complex sampling design. Probit analysis and median age at entry into a maturity stage and its fiducial limits were calculated using SAS 8.2. RESULTS: Reference data for age at entry for maturity stages are presented in tabular and graphical format. Non-Hispanic black girls had an earlier sexual development for pubic hair and breast development either by median age at entry for a stage or for the mean age for a stage than Mexican American or non-Hispanic white girls. There were few to no significant differences between the Mexican American and non-Hispanic white girls. Non-Hispanic black boys also had earlier median and mean ages for sexual maturity stages than the non-Hispanic white and Mexican American boys. CONCLUSION: Non-Hispanic black girls and boys mature early, but US children completed their sexual development at approximately the same ages. The present reference data for the timing of sexual maturation are recommended for the interpretation of assessments of sexual maturity in US children.

Predicting overweight and obesity in adulthood from body mass index values in childhood and adolescence.

BACKGROUND: The Centers for Disease Control and Prevention (CDC) introduced the clinical use of the body mass index (BMI; in kg/m(2)) in growth charts for young males and females. OBJECTIVE: This study updates our previous report with the use of new CDC BMI charts and definitions of adult overweight and obesity to predict adult overweight or obesity. DESIGN: Logistic models were fitted to relate adult overweight and obesity to childhood and adolescent BMI values at each age for 166 males and 181 females in the Fels Longitudinal Study and were applied to predict adult overweight and obesity at the 75th, 85th, and 95th percentiles on the CDC charts of childhood and adolescent BMI. RESULTS: A child or adolescent with a high BMI percentile on the CDC BMI-for-age growth charts has a high risk of being overweight or obese at 35 y of age, and this risk increases with age. For example, the probability of adult obesity at the 85th percentile for young males was

2000 CDC Growth Charts for the United States: methods and development.

OBJECTIVES: This report provides detailed information on how the 2000 Centers for Disease Control and Prevention (CDC) growth charts for the United States were developed, expanding upon the report that accompanied the initial release of the charts in 2000. METHODS: The growth charts were developed with data from five national health examination surveys and limited supplemental data. Smoothed percentile curves were developed in two stages. In the first stage, selected empirical percentiles were smoothed with a variety of parametric and nonparametric procedures. In the second stage, parameters were created to obtain the final curves, additional percentiles and z-scores. The revised charts were evaluated using statistical and graphical measures. RESULTS: The 1977 National Center for Health Statistics (NCHS) growth charts were revised for infants (birth to 36 months) and older children (2 to 20 years). New body mass index-for-age (BMI-for-age) charts were created. Use of national data improved the transition from the infant charts to those for older children. The evaluation of the charts found no large or systematic differences between the smoothed percentiles and the empirical data. CONCLUSION: The 2000 CDC growth charts were developed with improved data and statistical procedures. Health care providers now have an instrument for growth screening that better represents the racial-ethnic diversity and combination of breast- and formula-feeding in the United States. It is recommended that these charts replace the 1977 NCHS charts when assessing the size and growth patterns of infants, children, and adolescents.

Centers for Disease Control and Prevention 2000 growth charts for the United States: improvements to the 1977 National Center for Health Statistics version.

OBJECTIVE: To present a clinical version of the 2000 Centers for Disease Control and Prevention (CDC) growth charts and to compare them with the previous version, the 1977 National Center for Health Statistics (NCHS) growth charts. METHODS: The 2000 CDC percentile curves were developed in 2 stages. In the first stage, the empirical percentiles were smoothed by a variety of parametric and nonparametric procedures. To obtain corresponding percentiles and z scores, we approximated the smoothed percentiles using a modified LMS estimation procedure in the second stage. The charts include of a set of curves for infants, birth to 36 months of age, and a set for children and adolescents, 2 to 20 years of age. RESULTS: The charts represent a cross-section of children who live in the United States; breastfed infants are represented on the basis of their distribution in the US population. The 2000 CDC growth charts more closely match the national distribution of birth weights than did the 1977 NCHS growth charts, and the disjunction between weight-for-length and weight-for-stature or length-for-age and stature-for-age found in the 1977 charts has been corrected. Moreover, the 2000 CDC growth charts can be used to obtain both percentiles and z scores. Finally, body mass index-for-age charts are available for children and adolescents 2 to 20 years of age. CONCLUSION: The 2000 CDC growth charts are recommended for use in the United States. Pediatric clinics should make the transition from the 1977 NCHS to the 2000 CDC charts for routine monitoring of growth in infants, children, and adolescents.

Statistical effects of varying sample sizes on the precision of percentile estimates.

The present study evaluates the precision of outlying percentile estimates, with age- and sex-associated variations and facilitates decisions needed to revise the current NCHS 1977 Growth Charts with regard to 1) the inclusion of 3(rd) and 97(th) percentiles and 2) the selection of survey data for the construction of the revised growth charts. Simulation was performed to obtain data with distribution characteristics similar to those of The Third National Health and Nutritional Examination Survey (NHANES III) (1988-1991) data. NHANES III consists of a two-phase, 6-year, complex stratified multistage probability cluster, cross-sectional survey conducted from 1988 through 1994 to represent the US noninstitutionalized population. Phase I of the survey consisted of 679 boys and 622 girls in age groups 3, 8, 13, and 18 years. Weight and stature, the body mass index (BMI) (weight/stature(2); kg/m(2)) was calculated. The results show that 1) the precision of the percentile estimates is greater for stature than for weight and BMI, 2) percentiles during the pubertal period are less precise than those during the prepubertal and postpubertal periods for weight and BMI but there is little difference for stature, and 3) percentile estimates are more precise for girls than boys for weight and BMI, but not for stature. The present findings suggest that pooling of NHANES III and earlier National Center for Health Statistics (NCHS) survey data is necessary to achieve reasonable precision for the 3(rd) and 97(th) percentile estimates. Am. J. Hum. Biol. 12:64-74, 2000. Copyright 2000 Wiley-Liss, Inc.

Weight, stature, and body mass index data for Mexican Americans from the third national health and nutrition examination survey (NHANES III, 1988-1994).

Selected age- and sex-specific percentiles are presented for 4,054 Mexican American children ages 1-18 years who were included in the third National Health and Nutrition Examination Survey (NHANES III, 1988-1994). These percentile values are compared with corresponding percentiles for Mexican Americans from the Hispanic Health and Nutrition Examination Survey (HHANES, 1982-1984). In each sex, the weight and weight/stature(2) percentiles from NHANES III were significantly larger than those from HHANES. For weight, the NHANES III values tended to be clearly larger after 11 years in males and females, and they were larger for weight/stature(2) at the 50th and 90th percentiles in each sex after 6 years. For stature, the NHANES III values were significantly larger at the 90th percentile among females, but the differences were not significant for any other percentiles among females or males. In comparison with non-Hispanic White children, Mexican American children tend to be shorter and heavier, especially after the preschool period. The similarity of the findings for stature from NHANES III and HHANES indicates that the shorter statures of Mexican Americans are not cohort-specific. The tendency to larger values for weight/stature(2) in Mexican Americans has important public heath implications since this ratio tends to track after early childhood, and high ratios in adulthood constitute an important risk factor for common diseases such as diabetes mellitus and coronary heart disease. Am. J. Hum. Biol. 11:673-686, 1999. Copyright 1999 Wiley-Liss, Inc.

Decanalization of weight and stature during childhood and adolescence.

The probabilities that children and adolescents alter their positions to non-adjacent canals (decanalization) on the current NCHS growth charts have been estimated. In this context, canals are the zones between the major percentile levels (5th, 10th, 25th, 50th, 75th, 90th, and 95th) that are shown on the charts. These probabilities were calculated for one- and 2-year intervals, beginning at each annual age from 3-16 years, using serial data for weight and stature from 329 male and 303 female participants in the Fels Longitudinal Study. The probabilities of particular types of decanalizations, categorized by the initial canal and the direction of the change in relative level (decrease/loss; increase/gain) are presented. The probabilities for 1-year intervals were very low and, therefore, they are not presented. Additionally, probabilities were calculated for transitions from the canal between the 5th and 10th percentiles to the zone below the 5th percentile and from the canal between the 90th and 95th percentiles to the zone above the 95th percentile. Both these transitions are shifts to levels that are outside the normal range, and are more common than decanalization. The probabilities of decanalization and of transitions from the normal range were generally larger for weight than for stature except for transitions from the canal between the 90th and 95th percentiles to the zone beyond the 95th percentile. The probabilities for both weight and stature tended to be larger for changes toward the medians than for changes from the medians. Decanalizations that involved increases in level were significantly related to advanced skeletal maturation at ages younger than the usual age of peak height velocity and to retarded skeletal maturation at ages older than the usual age of peak height velocity. Am. J. Hum. Biol. 10:351-359, 1998. © 1998 Wiley-Liss, Inc.

Serial changes in blood pressure from childhood into young adulthood for females in relation to body mass index and maturational age.

This study determines: (1) patterns of change from childhood to young adulthood in body mass index (BMI), systolic blood pressure (SBP), and diastolic blood pressure (DBP), (2) effects of elevated BMI values on changes in blood pressures (BP), (3) extent of tracking for SBP, DBP, and BMI, and (4) prediction of future risk for elevated BP from earlier values. Annual serial BP and BMI data were available for 198 white females, ages 8-22 years, enrolled in the Fels Longitudinal Study. Patterns of change in BMI were described by a random effects model with a time series model for the correlated residuals. Serial BMI measures were differentiated from age-specific means to measure relative individual BMI levels. Serial BP were analyzed using a similar model to the BMI where relative individual BMI levels were included as an explanatory variable. There was a general increasing trend for SBP, DBP, and BMI from 8-22 years, but the rates of increase declined with age. At the same chronological age, early menarche females had a significantly greater BMI mean value than late menarche females. An average increase of 1 kg/m2 in deviation from BMI population means resulted in an average increase of 1.2 mmHg in SBP and 0.6 mmHg in DBP. Having SBP and DBP levels 1 standard deviation above mean levels, relative to females at mean levels, as early as age 9 represents an odds ratio of 2 for exceeding national 75th percentile levels of SBP and DBP at age 21. Am. J. Hum. Biol. 10: 589-598, 1998. © 1998 Wiley-Liss, Inc.

Longitudinal assessment of hormonal and physical alterations during normal puberty in boys. IV: Predictions of adult height by the Bayley-Pinneau, Roche-Wainer-Thissen, and Tanner-Whitehouse methods compared.

To determine how accurately the Roche-Wainer-Thissen (RWT), Tanner-Whitehouse (TW2), and Bayley-Pinneau (BP) prediction models estimated adult height, serial height predictions were made for 23 healthy boys (mean initial age 10.4 ± 1.1 years) every 8 months from 8-15 years of age. The RWT model was tested using Greulich-Pyle (RWT-GP) and Fels (RWT-Fels) bone ages. Stature was measured every 4 months until near final height was attained (growth rate <1cm · 8 mo-1). Mean age at near final height was 18.4 ± 1.4 years. To assure that the predictions were as accurate and precise as possible, bone age assessments were made by experts in each method. To investigate the influence of maturation on the predictions, the boys were grouped by Fels bone ages: <11 yr, 11-13.99 yr, and 14-14.99 yr. Comparison of the prediction bias and of the root mean square errors (RMSE) showed that the TW2 model gave the most accurate results, followed by the RWT and BP models. The adult height was generally underpredicted by the TW2 model and overpredicted by the RWT and BP models. The RMSE was reduced for each of the models as the bone age approached maturity. The TW2 model had the smallest average RMSE in all bone age groups. In the <11 yr bone age group, the RWT-Fels, RWT-GP, and BP models produced RMSEs that were 16.4%, 18.4%, 62.1%, respectively, greater than the TW2 model. For the 11-13.99 yr group, RMSE by the RWT-Fels, RWT-GP, and BP models were 7.5%, 18.0%, and 15.2%, respectively, greater than the TW2 model. In the 14-14.99 yr group the RWT-GP model had a 45.5% greater RMSE than the TW2 model, whereas the RWT-Fels model produced a RMSE only 15.2% greater than TW2. The RWT-Fels model produced a lower RMSE than the RWT-GP model for all bone age groups. Although the data are probably as accurate and precise as presently possible, biologically significant error remains, especially with overprediction of adult height in normally growing boys by the BP and RWT models. It is recommended that regardless of the prediction model implemented, caution be used when advising patients of their predicted adult height since all of the models tested had outlying predictions. Am. J. Hum. Biol. 9:371-380, 1997. © 1997 Wiley-Liss, Inc.

The decanalization of weight, recumbent length, and head circumference during infancy.

This study has estimated the extent to which 659 infants in the Fels Longitudinal Study maintained their positions in canals on the current NCHS growth charts during 6- and 12-month intervals. These canals are the zones between adjacent major percentile lines (5th, 10th, 25th, 50th, 75th, 90th, and 95th) on the growth charts. The probabilities of increases or decreases in level by two or more canals were calculated. Additionally, the probabilities were calculated for changes in level from between the 5th and 10th percentiles or between the 90th and 95th percentiles to zones beyond the 5th or 95th percentiles, respectively (transitions from normal limits). The analyses were made from birth to 36 months for weight and from 1-36 months for length and head circumference. The probabilities of decanalization were larger for weight than for length or head circumference for the interval from birth to 6 months, but not later. The probabilities for each variable analyzed tended to be large for young age intervals and larger for changes toward the medians than for changes from the medians. The directions of decanalization for weight from birth to 6 months were related to birth weight and those for length were related to midparent stature for the intervals from 6-12 months in each sex, 1-12 months in girls, and 6-18 months in boys. Am. J. Hum. Biol. 9:689-698, 1997. © 1997 Wiley-Liss, Inc.

Reference data for arm muscle and arm adipose tissue areas in Mexican Americans from the Hispanic Health and Nutrition Examination survey (HHANES 1982-1984): Comparisons with whites and blacks from NHANES II (1976-1980).

Data for arm muscle area (AMA) and arm adipose tissue area (AATA) from 3695 Mexican American children 6 months to 18 years of age included in HHANES (1982-1984) were used to obtain age-and gender-specific means and selected percentiles. These statistics were compared with those for non-Hispanic white and non-Hispanic black children from NHANES II (1976-1980). In comparison with non-Hispanic white and non-Hispanic black children, the Mexican American children tended to have smaller means and percentile values for AMA but larger values for AATA. There was considerable sexual dimorphism in AMA and AATA. Within each population, boys tended to have larger means and percentile values for AMA than girls, and girls tended to have larger values for AATA than boys. Within each population of boys, there was a prepubescent gain in AATA, followed by a midpubescent loss, and then an increase near the middle of the second decade. This "fat wave" pattern was not noticeable in girls. Population differences in age- and gender-specific mean values for AMA and AATA were small. Few statistically significant differences were observed; these were no more common than would occur by chance. Therefore, population-specific reference data for AMA and AATA may not be needed for the clinical evaluation of Mexican Americans, non-Hispanic blacks, and non-Hispanic whites. © 1996 Wiley-Liss, Inc.

Relationship of skeletal age to limb composition during pubescence.

The relationships between skeletal age (SA) and limb composition (arms, legs, and all four limbs) in terms of fat mass (FM), fat-free mass (FFM), muscle mass (MM) and bone mineral content (BMC) were investigated in 55 males and 53 females aged 9-15 years. The Fels method was used to assess hand-wrist SAs which were expressed as SA/chronological age (SA/CA). The limb composition data were obtained from a Lunar dual-energy x-ray absorptiometer using 3.6z software. The means for the limb composition variables increased gradually with age except in males for whom FM decreased from 12 to 13 years, and FFM and MM increased markedly from 13 to 14 years. There were similar findings when the limb composition data were expressed as percentages of body weight. All of the regressions of SA/CA on limb composition variables had positive slopes. Each of the slopes was significant for males, but nonsignificant for females. © 1996 Wiley-Liss, Inc.

Head circumference for Mexican American infants and young children from the Hispanic health and nutrition examination survey (HHANES 1982-1984): Comparisons with Whites and Blacks from NHANES II (1976-1980).

This study presents descriptive statistics for head circumference in Mexican American children 6 months to 7 years of age using data from the Hispanic Health and Nutrition Examination Survey (HHANES, 1982-1984) and compares these statistics with national estimates of head circumference for non-Hispanic White children and non-Hispanic Black children from the Second National Health and Nutrition Examination Survey (NHANES II, 1976-1980). Head circumference was measured in the same standardized fashion in the two surveys. The patterns of change with age in means and in empirical percentiles were similar for both genders and for all three ethnic groups. Values for head circumference increased with age, but the rate of increase became less as age advanced. Analyses indicated that at 1, 2, and 4 years of age, mean values for head circumferences for non-Hispanic White boys were significantly larger than those for Mexican American boys. The differences in mean values for head circumferences ranged from 0.7 to 1.1 cm. Because ethnic differences in head circumferences are small in magnitude, ethnic-specific sets of reference data for head circumference are not needed for clinical evaluation of Mexican Americans, non-Hispanic Whites, and non-Hispanic Blacks. Further analyses may be necessary when additional information from NHANES III allows the calculation of the 5th and 95th percentiles for Black and Mexican American children with small confidence limits. © 1995 Wiley-Liss, Inc.

Sarcopenia: A critical review of its measurements and health-related significance in the middle-aged and elderly.

A summary of the work performed by Stanley Garn relating to muscle mass while he worked at the Fels Research Institute is followed by a critical review of the measurement of sarcopenia, which is a deficiency of muscle mass, and its implications for health. The only satisfactory data for total muscle mass come from one cadaver study of a small selected sample. Analyses in relation to health (mortality rates) are limited to indices of muscle mass of which the body mass index (BMI) and arm muscle area or circumference are the most important because large amounts of serial data are available for analysis. The association between low BMI values and increased mortality rates is well established. Multiple studies, some of large samples, indicate that the increased mortality in those with low BMI values at entry is not fully explained by smoking behavior or disease at entry. There are, however, contrary findings from one major study. Associations between arm muscle circumference or area with mortality rates have also been reported. Independent effects of low BMI and low arm muscle values on mortality rates could be due to effects of low fat-free mass, particularly low muscle mass, on host defense mechanisms and risk factors for disease but few relevant data have been reported. © 1994 Wiley-Liss, Inc.

Family resemblance for Preece-Baines growth curve parameters in the fels longitudinal growth study.

The Preece-Baines Model 1 (PB1) nonlinear regression equation was fit to serial stature measurements from 456 participants in the Fels Longitudinal Growth Study. The resulting model parameters and derived biological parameters, such as age, stature, and velocity at take-off (TO) and peak velocity (PV) are analyzed for family resemblance in 228 nuclear families through estimation of familial correlations and path coefficients. Significant family resemblance was found for all of the growth parameters. Transmissibility estimates ranged from 41%-71%, suggesting that some of the factors controlling the timing and shape of the adolescent growth spurt are transmitted from parent to child. Significant gender effects were found in sibling resemblance, with brother-brother pairs more similar than other pairs for age at TO and PV and sister-sister pairs more alike for stature at TO and PV and for velocity at PV. © 1993 Wiley-Liss, Inc.

Development of reference data for increments in variables related to growth.

This paper directs attention to the progress made during the last few decades in methods for the development of reference data for increments and in the application of such data. This progress is exemplified by analyses of increments in recumbent length during infancy based on data from the Fels Longitudinal Study that have led to the development of reference data that can be applied easily to individuals and groups. The methods used to develop incremental reference data have improved considerably, but further progress is needed to construct better models, to refine the procedures for fitting models, and to simplify the application of incremental reference data. © 1992 Wiley-Liss, Inc.