title: Body mass index and timing of pubertal initiation in boys.
abstract: OBJECTIVE
  To examine the association between body mass index (BMI [calculated as weight in kilograms divided by height in meters squared]) and timing of pubertal onset in a population-based sample of US boys.
  
  
  METHODS
  Longitudinal prospective study.
  
  
  METHODS
  Ten US sites that participated in the National Institute of Child Health and Human Development Study of Early Child Care and Youth Development.
  
  
  METHODS
  Of 705 boys initially enrolled in the study, information about height and weight measures and pubertal stage by age 11.5 years was available for 401 boys.
  
  
  METHODS
  The BMI trajectory created from measured heights and weights at ages 2, 3, 4.5, 7, 9, 9.5, 10.5, and 11.5 years.
  
  
  METHODS
  Onset of puberty at age 11.5 years as measured by Tanner genitalia staging.
  
  
  RESULTS
  Boys in the highest BMI trajectory (mean BMI z score at age 11.5 years, 1.84) had a greater relative risk of being prepubertal compared with boys in the lowest BMI trajectory (mean BMI z score at age 11.5 years, -0.76) (adjusted relative risk = 2.63; 95% confidence interval, 1.05-6.61; P = .04).
  
  
  CONCLUSIONS
  The relationship between body fat and timing of pubertal onset is not the same in boys as it is in girls. Further studies are needed to better understand the physiological link between body fat and timing of pubertal onset in both sexes.
authors.affiliation: Division of Pediatric Endocrinology, Child Health Evaluation and Research Unit, University of Michigan, 300 NIB, Room 6E08, Campus Box 5456, Ann Arbor, MI 48109-5456, USA. joyclee@umich.edu
authors.forename: Joyce M
authors.initials: JM
authors.lastname: Lee
authors.forename: Niko
authors.initials: N
authors.lastname: Kaciroti
authors.forename: Danielle
authors.initials: D
authors.lastname: Appugliese
authors.forename: Robert F
authors.initials: RF
authors.lastname: Corwyn
authors.forename: Robert H
authors.initials: RH
authors.lastname: Bradley
authors.forename: Julie C
authors.initials: JC
authors.lastname: Lumeng
mesh_terms: D000273:Adipose Tissue; D001827:Body Height; D015992:Body Mass Index; D001835:Body Weight; D002675:Child, Preschool; D005500:Follow-Up Studies; D005837:Genitalia, Male / Q000254:growth & development; D006801:Humans; D008297:Male; D011159:Population Surveillance; D011446:Prospective Studies; D011627:Puberty / Q000502:physiology*; D013997:Time Factors