Why Are 7- and 8-Year-Old Girls Entering Puberty? There’s new research.
New insights into early onset development
In August this year, we learned that lots of seven- and eight-year-old girls are sprouting breasts. A study in the journal Pediatrics reported that 10 percent of white and 23 percent of black seven-year-olds, and 18 percent and 43 percent of eight-year-olds, are showing signs of sexual maturity.
It wasn’t the first time “precocious puberty” made headlines, but the numbers appear to be sliding even earlier. Last year in a Pediatrics study, it was reported that breast development started at an average age of almost 11 years in 1991 and 10 years in 2006. Indeed, most of the numbers out there indicate that girls in puberty have been getting progressively younger since the mid-1800′s. The trend used to signal a healthier population – the result of improved nutrition and lower incidence of disease. But that reasoning can only go so far.
It’s an unsettling idea – kind of creepy, actually – that something in our modern world could be messing with our kids’ biological clocks. Recently, a lot of explanations have been posed and red flags raised about the causes. Which ones should we pay most attention to?
Divorce or, more specifically, not having a biological father in the house was recently linked to early puberty. Absent dads in middle-class homes increased the risk of early breast development in girls ages six to eight. Family stress and insecure attachments spur on early sexual maturity, says Jay Belsky, a researcher who, in a separate study this year, reported that babies who didn’t smile, vocalize, and reach for mom (signs of secure attachment) started puberty earlier. Belsky’s explanation is that when times are tough, nature kicks in to start puberty earlier, because it ups the chance of a person mating and having offspring before it’s too late.
Other suspects include our old friends bisphenol-A (BPA) and phthalates. There is reason to think these compounds act on the body’s endocrine system, influencing how hormones are made and released. BPA (a building block of plastics) mimics estrogen, while phthalates (chemicals in soft plastics, cosmetics, and more) block the effects of testosterone and have been found to lower sperm count, for example, in male animals.
But if family stress and environmental toxins are scooching girls toward faster development, the effects are probably small. First of all, I’m not sure I buy that insecure homes speed up development, because as we’ve seen, when nutrition (one of the best indicators of a secure environment) improved, puberty age went down. And we can only speculate about endocrine-disrupting chemicals; yes we have some animal data, but it’s incredibly hard to sift apart the direct effects of one chemical on humans when we’re exposed to so many every day. One of the Pediatrics researchers is currently testing girls’ blood to look for more direct evidence of this link.
The most likely culprit of precocious puberty is the obesity epidemic. Overweight girls are 50 percent more likely to enter puberty early, and those considered obese have an 80 percent chance of developing breasts before their ninth birthday. In this country, nearly one third of children and teens are overweight or obese.
Why would fat signal the body to mature faster? Probably by tripping the hormone system that starts puberty in the first place. In the normal pre-teen brain, a grape-sized structure called the hypothalamus starts secreting the chemical GnRH, which then, by way of the pituitary gland, tells the ovaries and testes to make estrogen and testosterone, and in girls, “breast buds” are usually the first result. While this process is normal, chubbier children have more of the chemical leptin, which can stimulate the release of GnRH, as well as the pituitary’s hormones.
It’s important to point out that all these studies talk about the dropping age of breast development (a subjective measurement), but meanwhile the age of the most objective measure of puberty – the age of girls’ first periods – has stayed more or less stable, at just over 12 years, over the decades. No one knows what this means, but I take comfort in the fact that the most concrete marker of sexual development hasn’t budged.
Still there are plenty of reasons to be suspicious of toxins in our everyday products. The F.D.A. doesn’t require that manufacturers prove their safety before they are used — the burden of proof goes the other way around. But the body’s hormone system is complex, as is the combination of chemicals and other exposures our kids have every day of their lives, which makes it difficult to point the figure at one particular chemical.
Just to be safe, however, it probably makes sense to buy BPA-free bottles and be aware of phthalates – more products are labeling for this purpose, and why not hedge your bets? But in the trend towards earlier training bras for girls, our nation’s expanding waistline is probably the guilty party.
It sounds like comparing something subjective (breast buds) with objective (onset of menarche). One has changed and one has stabilised. I would guess that methods of measuring breast buds have changed/are not standardised/open to interpretation. Slate ran a good article on this a while ago.
DB: exactly – measuring breast tissue is subjective. The researchers say they’ve used the same methods over the years in long term studies, but we’re talking decades between samples – how can you be sure?
I have heard much talk about a link between early puberty in humans and growth hormones given to farm animals whose products we eat. I’m surprised there was nothing about that in this article.
@animalhormones -I’ve heard the same about animal hormones given to cows that end up in our milk as the cause too. Also surprised not to read that argument in this article. To me, seems like the most reasonable explanation.
So, soon we’ll be seeing toddlers with tampons? Is that where we’re getting at here?
Another possibility comes from epigenetics – the theory that something in earlier generations has spurred earlier breast development. But I agree, it is odd that we’ve heard so much about early puberty over the last decade but girls aren’t menstrating any earlier (as always, thanks for covering the topic without the hype!!). I’m also suspicious about how breast development has been assessed over the years, and we’ve had those same Tanner scales for decades, you’d think we moms and dad would have something better to go by thes days. Though I admire plenty of Jay Belsky’s work, I find it hard to believe that insecure social attachment in infancy could trigger early breast development. Sounds like a confounding factor or two! are missing from the equation. And if we’re talking evolutionary biology/psychology (which is always interesting but let’s face it, highly speculative) – if the goal is to procreate as soon as possible, why not menstrate earlier? Anyhow, it will be interesting to mine the data over the next decade when we can start to find groups of girls who haven’t had the hormones in milk, meat, etc. and of course, the bpa and phthalates.
Another possibility comes from epigenetics – the theory that something in earlier generations has spurred earlier breast development. But I agree, it is odd that we’ve heard so much about early puberty over the last decade but girls aren’t menstrating any earlier (as always, thanks for covering the topic without the hype!!). I’m also suspicious about how breast development has been assessed over the years, and we’ve had those same Tanner scales for decades, you’d think we moms and dad would have something better to go by thes days. Though I admire plenty of Jay Belsky’s work, I find it hard to believe that insecure social attachment in infancy could trigger early breast development. Sounds like a confounding factor or two! are missing from the equation. And if we’re talking evolutionary biology/psychology (which is always interesting but let’s face it, highly speculative) – if the goal is to procreate as soon as possible, why not menstrate earlier? Anyhow, it will be interesting to mine the data over the next decade when we can start to find groups of girls who haven’t had the hormones in milk, meat, etc. and of course, the bpa and phthalates.
I didn’t quite follow some of the writing – is it that having a single parent leads to stress, which is supposed to contribute? Or there is some physical correlation with having a biological father? As those of us who are adopted by happy families no, having no biodad (or biomom) doesn’t always mean living in stress or misery.
There is some interesting research, Danish I think, that follows adopted children and immigrant children from the same countries. The adoptees had a much higher rate of early puberty….lending some credence to the early trauma as well as the idea that abrupt nutritional changes (that adoptees but not immigrants experience) might be involved. I’m involved in the adoption community and many, many of us have daughters who entered puberty early (mine is from Ethiopia)