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      Timing of puberty in boys and girls: A population‐based study

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          Abstract

          Background

          A secular trend towards earlier puberty has been observed in girls, while a similar trend has been more uncertain in boys. We estimated current ages at pubertal development in both boys and girls.

          Methods

          In this population‐based cohort study, 14 759 of 22 439 invited boys and girls born from 2000 to 2003 in the Danish National Birth Cohort gave half‐yearly self‐reported information on puberty from the age of 11.5 years and throughout puberty. This late start of follow‐up limits the estimation of age at onset of puberty but not later pubertal milestones. We estimated mean age at attaining the following pubertal milestones in years with 95% confidence intervals ( CI): age at menarche, voice break, first ejaculation of semen and Tanner stages for pubic hair development and breast development or genital development. Further, the difference in mean age at menarche between mothers and daughters was estimated.

          Results

          In boys, voice break occurred at 13.1 (95% CI 13.0, 13.1) years, first ejaculation of semen occurred at 13.4 (95% CI 13.3, 13.4) years, and Tanner Genital Stage 5 occurred at 15.6 (95% CI 15.5, 15.6) years. In girls, age at menarche occurred at 13.0 (95% CI 13.0, 13.1) years and Tanner Breast Stage 5 occurred at 15.8 (95% CI 15.7, 15.9) years. Daughters had menarche 3.6 (95% CI 3.1, 4.2) months earlier than their mothers had.

          Conclusion

          These data indicate that age at menarche has declined and to some extent support a decline in age at attaining other markers of pubertal development among boys.

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          Most cited references24

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          The epidemiology of obesity.

          In the United States, obesity among adults and overweight among children and adolescents have increased markedly since 1980. Among adults, obesity is defined as a body mass index of 30 or greater. Among children and adolescents, overweight is defined as a body mass index for age at or above the 95th percentile of a specified reference population. In 2003-2004, 32.9% of adults 20-74 years old were obese and more than 17% of teenagers (age, 12-19 y) were overweight. Obesity varies by age and sex, and by race-ethnic group among adult women. A higher body weight is associated with an increased incidence of a number of conditions, including diabetes mellitus, cardiovascular disease, and nonalcoholic fatty liver disease, and with an increased risk of disability. Obesity is associated with a modestly increased risk of all-cause mortality. However, the net effect of overweight and obesity on morbidity and mortality is difficult to quantify. It is likely that a gene-environment interaction, in which genetically susceptible individuals respond to an environment with increased availability of palatable energy-dense foods and reduced opportunities for energy expenditure, contributes to the current high prevalence of obesity. Evidence suggests that even without reaching an ideal weight, a moderate amount of weight loss can be beneficial in terms of reducing levels of some risk factors, such as blood pressure. Many studies of dietary and behavioral treatments, however, have shown that maintenance of weight loss is difficult. The social and economic costs of obesity and of attempts to prevent or to treat obesity are high.
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            A structural approach to selection bias.

            The term "selection bias" encompasses various biases in epidemiology. We describe examples of selection bias in case-control studies (eg, inappropriate selection of controls) and cohort studies (eg, informative censoring). We argue that the causal structure underlying the bias in each example is essentially the same: conditioning on a common effect of 2 variables, one of which is either exposure or a cause of exposure and the other is either the outcome or a cause of the outcome. This structure is shared by other biases (eg, adjustment for variables affected by prior exposure). A structural classification of bias distinguishes between biases resulting from conditioning on common effects ("selection bias") and those resulting from the existence of common causes of exposure and outcome ("confounding"). This classification also leads to a unified approach to adjust for selection bias.
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              The Danish National Birth Cohort--its background, structure and aim.

              It is well known that the time from conception to early childhood has importance for health conditions that reach into later stages of life. Recent research supports this view, and diseases such as cardiovascular morbidity, cancer, mental illnesses, asthma, and allergy may all have component causes that act early in life. Exposures in this period, which influence fetal growth, cell divisions, and organ functioning, may have long-lasting impact on health and disease susceptibility. To investigate these issues the Danish National Birth Cohort (Better health for mother and child) was established. A large cohort of pregnant women with long-term follow-up of the offspring was the obvious choice because many of the exposures of interest cannot be reconstructed with sufficient validity back in time. The study needs to be large, and it is aimed to recruit 100,000 women early in pregnancy, and to continue follow-up for decades. The Nordic countries are better suited for this kind of research than most other countries because of their population-based registers on diseases, demography and social conditions, linkable at the individual level by means of the unique ID-number given to all citizens. Exposure information is mainly collected by computer-assisted telephone interviews with the women twice during pregnancy and when their children are six and 18 months old. Participants are also asked to fill in a self-administered food frequency questionnaire in mid-pregnancy. Furthermore, a biological bank has been set up with blood taken from the mother twice during pregnancy and blood from the umbilical cord taken shortly after birth. Data collection started in 1996 and the project covered all regions in Denmark in 1999. By August 2000. a total of 60,000 pregnant women had been recruited to the study. It is expected that a large number of gene-environmental hypotheses need to be based on case-control analyses within a cohort like this.
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                Author and article information

                Contributors
                nis.brix@gmail.com
                Journal
                Paediatr Perinat Epidemiol
                Paediatr Perinat Epidemiol
                10.1111/(ISSN)1365-3016
                PPE
                Paediatric and Perinatal Epidemiology
                John Wiley and Sons Inc. (Hoboken )
                0269-5022
                1365-3016
                11 October 2018
                January 2019
                : 33
                : 1 ( doiID: 10.1111/ppe.2019.33.issue-1 )
                : 70-78
                Affiliations
                [ 1 ] Department of Public Health, Section for Epidemiology Aarhus University Aarhus Denmark
                [ 2 ] Department of Epidemiology Fielding School of Public Health University of California Los Angeles California USA
                [ 3 ] Department of Public Health, Section for Biostatistics Aarhus University Aarhus Denmark
                [ 4 ] Department of Clinical Epidemiology Aarhus University Hospital Aarhus Denmark
                [ 5 ] Perinatal Epidemiology Research Unit Department of Paediatrics Aarhus University Hospital Aarhus Denmark
                Author notes
                [*] [* ] Correspondence

                Nis Brix, Department of Public Health, Section for Epidemiology, Aarhus University, Aarhus, Denmark.

                Email: nis.brix@ 123456gmail.com

                Author information
                http://orcid.org/0000-0002-1499-8401
                Article
                PPE12507
                10.1111/ppe.12507
                6378593
                30307620
                95cde33e-eb89-4ef6-bb58-584a1e50b5c3
                © 2018 The Authors. Paediatric and Perinatal Epidemiology Published by John Wiley & Sons Ltd

                This is an open access article under the terms of the http://creativecommons.org/licenses/by/4.0/ License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

                History
                : 02 May 2018
                : 25 July 2018
                : 21 August 2018
                Page count
                Figures: 1, Tables: 4, Pages: 9, Words: 7242
                Funding
                Funded by: Aarhus Universitet
                Funded by: Det Frie Forskningsråd
                Award ID: DFF ‐ 4183‐00152
                Funded by: Danish National Research Foundation
                Funded by: Danish Regional Committees
                Funded by: the Pharmacy Foundation
                Funded by: the Egmont Foundation
                Funded by: the March of Dimes Birth Defects Foundation
                Funded by: the Health Foundation
                Funded by: other minor grants
                Funded by: Novo Nordisk Foundation
                Award ID: 02‐2013‐2014
                Funded by: the Lundbeck Foundation
                Award ID: 195/04
                Award ID: R100‐A9193
                Funded by: Danish Medical Research Council
                Award ID: SSVF 0646
                Award ID: 271‐08‐0839/06‐066023
                Award ID: O602‐01042B
                Award ID: 0602‐02738B
                Funded by: the Innovation Fund Denmark
                Award ID: 0603‐00294B (09‐067124)
                Funded by: the Nordea Foundation
                Funded by: Aarhus Ideas
                Award ID: AU R9‐A959‐13‐S804
                Funded by: the University of Copenhagen Strategic Grant
                Award ID: IFSV 2012
                Categories
                Original Article
                Timing of Puberty
                Custom metadata
                2.0
                ppe12507
                January 2019
                Converter:WILEY_ML3GV2_TO_NLMPMC version:5.5.9 mode:remove_FC converted:18.02.2019

                Pediatrics
                cohort studies,humans,menarche,puberty,sexual development,sexual maturation
                Pediatrics
                cohort studies, humans, menarche, puberty, sexual development, sexual maturation

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