Portal de Periódicos da CAPES

Pubertal timing: is there any new news?

2005; Elsevier BV; Volume: 37; Issue: 5 Linguagem: Inglês

10.1016/j.jadohealth.2005.08.014

1879-1972

Charles E. Irwin,

Hypothalamic control of reproductive hormones

Are children today experiencing puberty at an earlier age than their parents, and if so, why? The earlier onset of puberty in the United States was first reported by Herman-Giddens et al in the late 1990s [[1]Herman-Giddens M.E. Slora E.J. Wasserman R.C. et al.Secondary sexual characteristics and menses in young girls seen in office practice a study from the Pediatric Research in Office Settings network.Pediatrics. 1997; 99: 505-512Crossref PubMed Scopus (1377) Google Scholar]. This cross-sectional, clinically based study documented that the prevalence of Tanner Stage 2 breast and pubic hair development at age eight years was 15% for White females and 48% for Black females, representing a significant increase in the percentage of children entering puberty at an earlier age than previously reported in national cross-sectional studies. In spite of earlier entry into puberty by the girls in the study, the timing of menarche for White females remained relatively stable; however, the onset of menses for Black females was earlier than reported in the HANES cycles II (1963–1965) and III (1966–1970) findings [[2]MacMahon B. Age at Menarche, United States. National Center for Health Statistics, Vital and Health Statistics, Washington, DC1973Google Scholar]. The publication of this study has spurred an ongoing debate in the medical literature and lay press over whether there is conclusive evidence of earlier onset of sexual maturation for females in the United States and if so, what its etiology might be [3Wu T. Mendola P. Buck G. Ethnic differences in the presence of secondary sex characteristics and menarche among US girls the Third National Health and Nutrition Examination Survey, 1988–1994.Pediatrics. 2002; 110: 752-757Crossref PubMed Scopus (317) Google Scholar, 4Sun S.S. Shume S. Schubert C.M. et al.National estimates of the timing of sexual maturation and racial differences among US children.Pediatrics. 2002; 110: 911-919Crossref PubMed Scopus (444) Google Scholar, 5Chumlea W.C. Schubert C.M. Roche A.F. et al.Age at menarche and racial comparisons in US girls.Pediatrics. 2003; 111: 110-113Crossref PubMed Scopus (555) Google Scholar, 6Biro F.M. McMahon R.P. Striegel-Moore R. et al.Impact of timing of pubertal maturation on growth in black and white female adolescents the National Heart, Lung and Blood Institute Growth and Health Study.J Pediatr. 2001; 138 (646–43)Abstract Full Text Full Text PDF Scopus (242) Google Scholar, 7Anderson S.E. Dallal G.E. Must A. Relative weight and race influence average age at menarche results from two nationally representative surveys of US girls studied 25 years apart.Pediatrics. 2003; 111: 844-850Crossref PubMed Scopus (403) Google Scholar, 8Herman-Giddens M.E. Kaplowitz P.B. Wasserman R. Navigating the recent articles on girls’ puberty in pediatrics what do we know and where do we go from here?.Pediatrics. 2004; 113: 911-916Crossref PubMed Scopus (100) Google Scholar]. Some have suggested environmental exposure, others better nutrition [9Freedman D.S. Khan L.K. Serdula M.K. et al.Relation of age at menarche to race, time period and anthropometric dimensions the Bogalusa Heart Study.Pediatrics. 2002; 110 (Available from: www.pediatrics.org/cgi/content/full/110/4/e3.): e43Crossref PubMed Scopus (292) Google Scholar, 10Staessen J.A. Nawrot T. Hond E.D. et al.Renal function, cytogenetic measurements, and sexual development in adolescents in relation to environmental pollutants a feasibility study of biomarkers.Lancet. 2001; 357: 1660-1669Abstract Full Text Full Text PDF PubMed Scopus (186) Google Scholar]. Most recently, some investigators have associated the earlier onset of puberty with the increased prevalence of obesity in the child population [11Kaplowitz P.B. Slora E.J. Wasserman R.C. et al.Earlier onset of puberty in girls relation to increased body mass index and race.Pediatrics. 2001; 108: 347-353Crossref PubMed Scopus (555) Google Scholar, 12Wang Y. Is obesity associated with early sexual maturation? A comparison of the association in American boys versus girls.Pediatrics. 2002; 110: 903-910Crossref PubMed Scopus (485) Google Scholar, 13Davison K.K. Susman E.J. Brich L.L. Percent body fat at age 5 predicts earlier pubertal maturation among girls at age 9.Pediatrics. 2003; 111: 815-821Crossref PubMed Scopus (223) Google Scholar]. In this issue of the Journal of Adolescent Health, Sun and his colleagues use data for U.S. children from three national health surveys over a 30-year period (1966–1994) to assess secular trends of pubertal onset and completion for both males and females [[14]Sun S.S. Schubert C.M. Liang R. et al.Is sexual maturity occurring earlier among U.S. Children?.J Adolesc Health. 2005; 37: 345-355Abstract Full Text Full Text PDF PubMed Scopus (67) Google Scholar]. They report their data by gender. For boys, the secular trends are limited to Whites and Mexican Americans. During this time period, the data on non-Hispanic White boys from NHANES III (1988–1994) is compared with the measurements from NHES (1966–1970). Non-Hispanic White boys in the later cohort were in Tanner Stage 2 in greater proportion, and they entered Stage 3 genital development and Stages 3 and 4 pubic hair development earlier than the boys in the 1966–1970 cohort. These data support the assumption of an earlier onset and progression through the stages of sexual maturation for the NHANES III (1988–1994) White boys. However, the non-Hispanic White boys in the 1988–1994 cohort were significantly later than NHES White boys in their ages at entry into Stage 5 genital development, and there were no significant differences in the ages at entry into Stage 5 pubic hair. These data indicate that non-Hispanic White boys may start puberty earlier but finish it later than the earlier cohort, if genital development is used as the measure of completion of sexual development. The analyses of the Mexican American boys compare the HHANES (1982–1984) data set with NHANES III (1988–1994). The findings for Mexican American boys are similar to those for non-Hispanic White boys, with earlier onset and higher genital development in greater proportion in Stages 3 and 4 genital development for the later cohort. Also, the completion of sexual maturation and entry into Stage 5 was not significantly different for the time period studied. For girls, there was no secular trend in sexual maturation for non-Hispanic Black girls or White girls between 1966–1970 and 1988–1994. When comparing the proportions of NHANES III (1988–1994) non-Hispanic White and Black girls in Stage 2 or higher breast development and pubic hair development at age 12–13 years compared with NHES (1966–1970), there were no differences. Similar to the non-Hispanic White boys, the girls completed sexual maturity later in the NHANES III when compared with the NHES data. The Mexican American data indicate earlier entry into puberty and more rapid progression through Tanner Stage 4, but in the final analysis, these girls reached Tanner Stage 5 later than the earlier cohort. Sun and his colleagues also report on the median ages for menarche. In both of the most recent cohorts, median menarche ages were 12.06 years for non-Hispanic Black girls, 12.25 for Mexican American girls, and 12.55 for non-Hispanic White girls. The 30-year difference is .46 years for Blacks and .25 for Whites. These median differences support a trend toward earlier completion of puberty in females. This study continues to raise many questions about measurement, onset, progression, and completion of puberty for both males and females. Even though the analyses offer no definitive proof of sexual maturity occurring earlier, there is clear evidence for earlier onset of puberty for non-Hispanic White males and, most recently, Mexican American males and females. Therefore, because the current data support the notion that puberty may be a lengthier process at this point, the question of tempo is a critical one. The debate in the literature about timing and completion of puberty has been focused almost entirely on females, but finally we have an article that gives us the perspective from the other side [[14]Sun S.S. Schubert C.M. Liang R. et al.Is sexual maturity occurring earlier among U.S. Children?.J Adolesc Health. 2005; 37: 345-355Abstract Full Text Full Text PDF PubMed Scopus (67) Google Scholar]. Possible factors responsible for this early initiation are not addressed. The authors unequivocally state that childhood obesity does not account for this earlier onset, despite recent evidence regarding the causal mechanism of earlier entry into puberty in girls with higher body mass indices (BMIs) [15Biro F.M. Lucky A.W. Simbartl L.A. et al.Pubertal maturation in girls and the relationship to anthropometric changes pathways through puberty.J Pediatr. 2003; 142: 643-646Abstract Full Text Full Text PDF PubMed Scopus (122) Google Scholar, 16Schubert C.M. Chumlea W.C. Kulin H.E. et al.Concordant and discordant sexual maturation among U.S. children in relation to body weight and BMI.J Adolesc Health. 2005; 37: 356-362Abstract Full Text Full Text PDF PubMed Scopus (24) Google Scholar]. Furthermore, the Mexican American children are not evaluated by birth status; there is some evidence that country of origin and immigrant status may contribute to under-nutrition and therefore, affect pubertal timing. Measurement of pubertal status remains a central concern; because these national data are reported by visual inspection rather than palpation as used in clinical practice, there may be a tendency to overestimate entry into puberty, given the increasing prevalence of obesity in the United States. As the authors state, there is also some concern about the problems associated with inter-survey comparisons of maturity stage at a younger age due to insufficient numbers in the dataset and the lack of entry of children into the study at an early enough age [[14]Sun S.S. Schubert C.M. Liang R. et al.Is sexual maturity occurring earlier among U.S. Children?.J Adolesc Health. 2005; 37: 345-355Abstract Full Text Full Text PDF PubMed Scopus (67) Google Scholar]. A final point should be considered in our continued study of pubertal maturation and its timing. These national and clinical studies, as they are currently constructed, are able to explain only associations. To truly understand the mechanisms of puberty and a possible change in onset, progression, and completion, we need longitudinal data from diverse samples of children. As the National Children’s Study continues to be planned in the United States, we need to encourage the coalition of federal agencies planning the study to make certain that the sample is diverse and of adequate size [[17]The National Children’s Study [cited 2005 Aug 20]. Available from: http://nationalchildrensstudy.gov/news/e-updates/e_update_072005.cfm.Google Scholar]. The study must include validated pubertal measures so that we may have definitive answers on the critical question of sexual maturity in children. We also need studies from our international colleagues. But this study is in its planning phase, and results will not be available for over a decade. We must take certain actions now. We need to continue to advocate for the establishment of consistent measures for assessing the onset of puberty; for the collection of pubertal status measures in the NHANES study on children as early as seven years of age; and for ongoing clinical studies to elicit the associations among obesity, under-nutrition, geographical location, and environmental toxins, and their impact on pubertal development.