Across America, Girls Are Beginning Puberty Younger

By Andrew Moseman | August 9, 2010 4:47 pm

girl-mathGirls around the country are starting puberty ever younger, says a new study out in Pediatrics.

Researchers led by Frank Biro studied more than a thousand girls between six and eight years old from New York, Cincinnati, and San Francisco. Their findings: By the age of 7, about 23 percent of black girls, 15 percent of Hispanic girls, and 11 percent of white girls showed enough breast development to be considered pubescent. Those numbers are even more extreme than the findings of a similar 1997 study that seemed to show the age entering puberty was dropping fast.

Says Biro:

“In 1997, people said, ‘That can’t be right; there must be something wrong with the study’. But the average age is going down even further” [Los Angeles Times].

The starkness of Biro’s statistics has drawn plenty of attention. But just what it means is a difficult question, because there’s no “ideal” age for entering puberty.

A girl needs a certain amount of body fat to start menstruating, and girls who are malnourished or ill may have delayed puberty. In developed countries, the age of puberty dropped from the 19th to 20th centuries, as nutrition improved and infectious diseases were brought under better control, and it was seen as a sign of progress [The New York Times].

However, seven and eight years old might be “too young,” given the possible psychological and medical effects. Going through puberty early might affect cancer risk by increasing one’s lifetime exposure to hormones like estrogen and progesterone, which can speed tumor growth in some cases. There are probably other consequences yet unknown.

And then, Biro says, there’s the concern of one’s physical and emotional maturity moving at different rates:

“For the 11-year-old that looks like she’s 15 or 16, adults are going to interact with her like she’s 15 or 16, but so are her peers.”… Girls who develop young “look physically older,” he said, adding, “It doesn’t mean that they’re psychologically or socially more mature” [New York Daily News].

The big question is why this is happening—studies in China and Denmark recently have picked up the same phenomenon. Biro’s study can’t address that part, but he has some ideas.

He speculates that its primary driver may be overweight and obesity, because estrogen is sequestered in fat tissue. But environmental exposures to chemicals — including pesticides and endocrine-disrupting chemicals like bisphenol A, commonly found in plastics, and phthalates, which are contained in many personal-care products — could also play a role [TIME].

Related Content:
DISCOVER: Girls Hit Puberty Earlier Around the World
DISCOVER: Growing Up in a Hurry
80beats: This Is Your Brain on Puberty: Study Probes Why Learning Slows for Teens
Gene Expression: Genes That Effect Female Development

Image: iStockphoto

CATEGORIZED UNDER: Health & Medicine
  • d
  • Donna F

    Maybe it is natures way of keeping the population going. Many modern women in developed countries are having less babies. To counter balance that girls are reaching puberty earlier. My daughter was 10 years old when she went through puberty.

  • blueshifter

    heh heh heh

  • Christina

    Donna: I don’t think the human population needs any help maintaining itself. Also, earlier puberty wouldn’t help much when women are increasingly delaying childbirth, even if there were need to help “keep the population going”

  • Darren Garrison

    Yet another way the Chinese are beating us…

  • m

    D – you are right. It was in a previous Discover article. It’s sad what journalism schools are churning out these days.

    I’m old enough to remember when Discover was run by people with a science background.

  • Eliza Strickland

    m – I’m not sure what your complaint is.

    D helpfully pointed out a link to a blog post about the possible effects of phthalates on young boys, while this article is about the age at which girls are entering puberty. It does seem possible that there’s a connection, and that both boys’ and girls’ sexual maturation is being affected by exposure to environmental chemicals. But that’s by no means proven, and this current study didn’t address that question directly.

    We strive every day to provide accurate, engaging coverage of the latest developments in science. If you’d like to offer your input on how we can do better, I ask that you do so politely.

    Eliza, DISCOVER online news editor

  • fatkid

    “Got milk?” Should be “Got hormones?” I can picture 10 yr. old girls chugging milk so their boobs grow bigger to keep up with the 11 yr. olds.

    What’s the impact of puberty on a 10 yr. Olds body down the line from the developmental tax placed on it now? It’s ironic that drinking milk may lead to osteoperosis..

  • Idlewilde

    I had early puberty, so I’m being careful about my health. iIm only 18, but I figure I’d better get into the habit early.

  • Lucas

    I believe we’re reverting back to old times when we matured early and started having children of our own by the age of 15/16 and therefor died early. I believe in evolution but I also believe in devolving. We read about great civilizations like the Ancient Egyptians. They were intelligent enough that we have no idea how they built things. When you get too good at what you’re here for you solve the equation and disappear. Maybe our bodies are doing the same thing here. Soon enough the life expectancy will also revert to a man living up until the age of 47 once more. We’re not made of special after all.

  • http://Discover Greg Fritz

    I just read your short story about girls showing puberty at younger ages. I am 54 years old and not being educated in this area, I have been telling friends for years this is happening as I have noticed this change over the last 20 years. I am not a scientist by any means. I have not read about this before but it is something I have believed for a log time. I think you should look at the food cows are fed and the milk additives combined with the hormones and other chemicals. From there look at anything else that uses this altered cow milk and any other human food products that may have some of the same additives as the cows food. This would include beef from the cows, all dairy products, pork products as the feeds are similar and so on. Think about it. If your over 50 like I am and you are aware of the subtle changes and advancements in bioengineering you would notice these changes as well. And now after reading about the plastics leaching chemicals out in the products the are made to contain further convinces me that the NEW ways of treating food products are not always better. IE: why do you think others only buy organinc foods and organic grown meat products. This not rocket science to me. if any of you folks feel I am close to being right I would like to know. I hope my thoughts are considered worthy of investigation.
    Serious Thinker in Michigan

  • Brian Too

    Haven’t we known about this for decades? Somehow I think this has been published since the 1960’s.

    To me this is simply a part of the larger trend towards good nutrition, improved health, longer lifespans, and so forth. How do we differentiate between superior public health factors that enable earlier puberty (which must have a metabolic cost associated), and something else going on like estrogen mimics?

  • http://Discover Dawn

    I feel Greg is on the right track. I do believe it’s the hormones that are added into our food (cows,pigs,and chickens) that is causing our kids to start puberty early. I just read an article that those who go through puberty early also has a higher rick of cancer. This scares me to death because I have a daughter and she is going through it early. I blame myself for us not eating more fresh food. Something needs to be done! More studies and less additives.


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