Past research has shown a steady decrease in the age that children -- specifically girls -- are hitting puberty. Evidence first surfaced in a study published in the journal Pediatrics in April 1997. In that study, researchers found that the average age for breast development or the growth of pubic hair was 9.7 years old for Caucasian girls and 8.1 years old for African-American girls. A number of subsequent studies have shown similar results -- that girls are "growing up" at younger and younger ages.
"This study adds to the literature in terms of looking at whether puberty is happening early so we can figure out what's causing it," said Dr. Elizabeth Alderman, professor of clinical pediatrics at the Albert Einstein School of Medicine.
So far, there's been no clear, singular explanation as to exactly why this is happening. One theory suggests girls' exposure to estrogens and other organic pollutants in the environment could be providing the early trigger that sets puberty into motion.
There are hypotheses that bisphenol A, or BPA in the environment could be triggering early puberty. Other environmental toxins which are believed to have an impact on pubertal age are parabens -- preservatives found in shampoos and other cosmetic products -- and phyoestrogens found in plants.
"None of these possible triggers have been studied adquately," said Budzak.
The authors of the current study concur. They wrote "[v]ariations in the timing of pubertal maturation may be sensitive 'sensors' of the effects of environmental exposure in human populations," and are in fact in the first year of a study looking whether environmental factors cause early puberty.
Another theory places blame on the growing epidemic of obesity among children because fat tissue is known to produce estrogen. But that theory raises questions of its own.
"If puberty happens earlier because girls are heavier, and gaining that weight is sending hormonal signals to start puberty earlier, is that really normal, or a sign of obesity, which is abnormal?" said Hollander.
One 2007 study seemed to suggest that a stressful family environment may cause puberty to kick in early for young girls. And in 2008, yet another study found a gene mutation that could be responsible for a small number of these cases.
Occasionally, precocious puberty can be the result of a tumor or other problem in the brain, or a brain injury or infection; these cases, however, are rare.
There are also endocrine disorders that can cause early puberty, including thyroid disease, polycystic ovarian syndrome and others.
"These are the types of things to screen for when a little girltarget="external" seems to be showing signs of early puberty," said Budzak.
Experts have conflicting opinions about whether or not this study will redefine what is normal in terms of early puberty.
According to Budzak, a new definition of normal can have huge treatment and evaluation implications. "If a girl is in this new range of normal, the child doesn't need to go through all the tests to evaluate something that is no longer abnormal," she said.
"It shows that it could be totally normal for an 8- or 9-year-old to have breast development," said Alderman.
Experts do agree that finding the cause for early puberty is important because of potential health concerns and developmental issues in the future.