Lack of linkage between height and weight and age at menarche during the secular shift in growth of Japanese children

Pubertal timing, bone acquisition, and risk of fracture throughout life

Pubertal maturation plays a fundamental role in bone acquisition. In retrospective epidemiological surveys in pre- and postmenopausal women, relatively later menarcheal age was associated with low bone mineral mass and increased risk of osteoporotic fracture. This association was usually ascribed to shorter time exposure to estrogen from the onset of pubertal maturation to peak bone mass attainment. Recent prospective studies in healthy children and adolescents do not corroborate the limited estrogen exposure hypothesis. In prepubertal girls who will experience later menarche, a reduced bone mineral density was observed before the onset of pubertal maturation, with no further accumulated deficit until peak bone mass attainment. In young adulthood, later menarche is associated with impaired microstructural bone components and reduced mechanical resistance. This intrinsic bone deficit can explain the fact that later menarche increases fracture risk during childhood and adolescence. In healthy individuals, both pubertal timing and bone development share several similar characteristics including wide physiological variability and strong effect of heritable factors but moderate influence of environmental determinants such as nutrition and physical activity. Several conditions modify pubertal timing and bone acquisition, a certain number of them acting in concert on both traits. Taken together, these facts should prompt the search for common genetic regulators of pubertal timing and bone acquisition. It should also open epigenetic investigation avenues to pinpoint which environmental exposure in fetal and infancy life, such as vitamin D, calcium, and/or protein supplies, influences both pubertal timing and bone acquisition.

Onset of breast and pubic hair development and menses in urban chinese girls

OBJECTIVES

To determine the current prevalence and mean ages of onset of pubertal characteristics in healthy urban Chinese girls.

METHODS

A cross-sectional study of sexual maturation of healthy Chinese girls was conducted in 9 representative cities of the eastern, western, southern, and northern parts and central region of China between 2003 and 2005. At examination, stages of breast and pubic hair development were rated on girls 3 through 19.83 years of age, and height and weight were also recorded. Data on menses were collected by the status quo method. Probit analysis was used to calculate the median age and 95% confidence interval (CI) for onset of breast and pubic hair development and menarche.

RESULTS

Data were analyzed for 20654 apparently healthy girls. At age 8 years, 19.57% of these girls had evidence of breast development. The median ages of onset of Tanner stages 2 and 3 for breast development were 9.20 (95% CI: 9.06-9.32) years and 10.37 (95% CI: 10.28-10.45) years, respectively. The median ages of onset of Tanner stages 2 and 3 for pubic hair development were 11.16 (95% CI: 11.03-11.29) years and 12.40 (95% CI: 12.25-12.55) years, respectively. Menses occurred at 12.27 years (95% CI: 12.16-12.39).

CONCLUSIONS

These data suggest that urban Chinese girls are actually experiencing earlier breast development than currently used norms. The up-to-date reference for normal pubertal development in urban Chinese girls needs to be established for the purpose of determining precocious puberty or pubertal delay.