Puberty: two studies & news item

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" The relationship between body fat and timing of pubertal onset is not

the same in boys as it is in girls. " (1)

1. *Body Mass Index and Timing of Pubertal Initiation in Boys (see also

cite-3)*

Joyce M. Lee et al.

Arch Pediatr Adolesc Med, Feb 2010; 164: 139 - 144.

http://tinyurl.com/ygvnrzt

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.

Design Longitudinal prospective study.

Setting Ten US sites that participated in the National Institute of

Child Health and Human Development Study of Early Child Care and Youth

Development.

Participants 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.

Main Exposure 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.

Main Outcome Measure 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.

2. *Longitudinal Development of Secondary Sexual Characteristics in

Girls and Boys Between Ages 91/2 and 151/2 Years*

J. Susman et al.

Arch Pediatr Adolesc Med. 2010;164(2):166-173.

http://archpedi.ama-assn.org/cgi/reprint/164/2/166

Objectives To identify ages when adolescents were in sexual maturity

stages 2 through 5; to explain the relations between breast (girls),

genital (boys), and pubic hair (girls and boys) development between ages

91/2 and 151/2 years; and to evaluate synchrony of pubertal development

across characteristics.

Design Annual pubertal assessments.

Setting Ten locations in the United States.

Participants A total of 859 adolescents (427 boys [49.7%] and 432 girls

[50.3%]; 737 white [85.8%] and 122 black [14.2%]).

Main Outcome Measures Changes in the 5 stages of breast, genital, and

pubic hair development.

Results Girls were in breast maturity stages 2 and 3 earlier than

comparable pubic hair stages. Although breast development in girls

started earlier than pubic hair development, girls completed breast and

pubic hair development at approximately the same age. Black girls were

in all stages of breast and pubic hair development earlier than white

girls. Boys were in stages 2, 3, 4, and 5 of genital development before

the comparable pubic hair stage. In boys, genital development started

earlier than pubic hair development, but pubic hair development was

completed in less time. Black boys were in genital and pubic hair

development about 7 months earlier than white boys. Black and white boys

completed genital development in approximately 41/2 years, but black

boys took approximately 6 months longer than white boys to complete

pubic hair development. At stage 2, for 66.2% of girls, breast

development preceded their pubic hair development; for 91.1% of boys,

genital development preceded their pubic hair development.

Conclusions The results of this study are useful in understanding

normative variation in the timing and change in the development of

secondary sexual characteristics at puberty. They will help identify

adolescents with atypical changes in sexual maturation and unusual

progression of sexual maturation and growth disorders.

3. *Obese boys more likely to begin puberty late: study finds

fat-puberty link that is opposite of girls'*

February 1, 2010 | 2:00 pm

http://latimesblogs.latimes.com/booster_shots/2010/02/fat-boys-more-likely-to-be\

gin-puberty-late-study-finds-fatpuberty-link-that-is-opposite-of-girls.html

While obesity has been shown to bring on puberty earlier in girls, a new

study finds the opposite trend for overweight boys: Male children whose

body-mass index (BMI) is consistently highest through early and

mid-childhood are significantly more likely than thinner boys to have

delayed puberty. (BMI is assessed somewhat differently for children and

teens than for adults. See here for kids' BMI calculators.)