A study of over 1,200 girls in three American cities revealed that young American girls are entering puberty at earlier ages (between seven and eight years of age) than studies investigating the age of puberty conducted 30 years ago. This new study published in the online journal Pediatrics used the Tanner Breast Stages system for defining puberty; this system uses a five-stage system for classifying breast development. The data indicated that the largest increase in girls entering puberty early are white girls with 10.4 percent of the seven year old girls studied showing breast development consistent with the signs of the onset of puberty. This percentage of girls entering early puberty is up from about five percent that was reported in a study conducted in 1997.
The results also indicated that the percentage of seven-year-old black (non-Hispanic) girls, and Hispanic girls who entered early puberty were 23.4 percent and 14.9 percent respectively. For girls entering early puberty at age eight, the percentages of girls was 18.3 percent (white), 42.9 percent (black non-Hispanic), and 30.9 percent (Hispanic). Of note, the researchers indicated that the proportion of girls who attained breast stage two developments varied by body mass index and site, although proportionally, obese girls reached puberty early.
The lead investigator of this study, Dr. Frank Biro from the Cincinnati Children???s Hospital Medical Center in Ohio, stated that this study was not necessarily representative of all of the young girls in the United States. Of course, this study does represent a trend in the U.S., so there may be important implications for the health of young girls. Dr. Biro also stated that there was no clear reason for the trend of these girls entering puberty early, although some potential factors cited include the genetic makeup of these girls, the environment, and how these two factors interact. Another potential causal factor is that these girls come into contact with chemicals that can mimic the effects of female hormones, such as estrogen.