Study Finds Earlier Onset of Puberty in Girls

Cincinnati—The age of onset of puberty in girls continues to decline.

A new study shows that the number of 7- and 8-year-old girls who have breast development is greater than that indicated in studies conducted 10 to 30 years earlier.

"What causes earlier onset of puberty isn’t entirely clear at this time, but we are looking closely at several different potential factors, including genes and environmental exposures, as well as how those two may interact with each other,” says lead author Frank Biro, MD, director of adolescent medicine at Cincinnati Children’s Hospital Medical Center and a professor of pediatrics at the University of Cincinnati (UC) College of Medicine.

The study is published online in the Aug. 9, 2010, issue of Pediatrics, the journal of the American Academy of Pediatrics. UC’s Paul Succop, PhD, and Susan Pinney, PhD, were collaborators in the study.

The study was conducted through the Breast Cancer and the Environment Research Centers, which were established in 2003 by the National Institute of Environmental Health Science and the National Cancer Institute.

Previous studies have shown a link between an earlier age of menarche (first menstrual period) and an increased risk of breast cancer. 

Biro and his colleagues studied over a period of time 1,239 girls between the ages of 6 and 8 from the Cincinnati area, East Harlem, N.Y., and the San Francisco area. The researchers used well-established criteria of pubertal maturation, including the five stages of breast development known as the Tanner Breast Stages.

The researchers found a higher prevalence of onset of breast development among girls at age 7 and 8, especially in white girls, compared to those observed in a study conducted more than 10 years ago and another study conducted 30 years earlier.

The Breast Cancer and the Environment Research Centers include UC, the Fox Chase Cancer Center in Philadelphia and collaborators at University of Alabama Birmingham and Mount Sinai School of Medicine, Michigan State University and the University of California San Francisco Comprehensive Cancer Center and Kaiser Permanente Northern California and Zero Breast Cancer. The epidemiology programs were established to conduct studies in pre- and early puberty girls, in recognition of puberty as a potential window of susceptibility for breast cancer.

The study was funded by a seven-year grant from the National Institute of Environmental Health Sciences and the National Cancer Institute.