Girls are developing breasts earlier, and everyone should be concerned. While any right-headed person would want to stop this trend, no one knows the cause. Yes, there are a great many theories, but theories are just hypotheses that need to be tested. You will read about the two biggest theories: Diet and diet. Diet-1 is that increased weight (i.e., diet) as measured by body mass index (BMI) is a possible culprit. Diet-2 is that what we eat and what is in what we eat is more important. This usually comes down to discussions about environmental estrogens. There is going to be a great deal of thrashing around by different public policy groups depending on their special interests. While I am generally not prone to being an alarmist, the collection of data on this subject is just plain scary.
Earlier this week, the Journal of Pediatrics released a new article that measures onset of puberty in young girls and compares it to past US data. The measure of puberty that is grabbing the headlines is that, according to the article, girls as young as 7 are developing breasts.
This study is startling but not, per se, a generally new finding. In fact, this is NOT an US issue. It is a worldwide issue. Lise Aksglaede, et al, found similar results in "Recent Decline in Age at Breast Development: The Copenhagen Puberty Study" (Copenhagen Study) published in Pediatrics in 2009. A quick search of the web or any medical database will find additional articles on the subject including research in numerous other countries.
The Copenhagen Study compared two groups of about 1,000 girls, each in 1991-1993 and 2006-2008. The study found that girls achieved breast development stage 2 at 10.86 years in the earlier group and 9.86 years in the later group. This is a one-year decrease in the development of breasts in a 15-year time frame! The authors state:
We found significantly earlier breast development among girls born more recently. Alterations in reproductive hormones and BMI did not explain these marked changes, which suggests that other factors yet to be identified may be involved.
So while BMI has a known association with earlier puberty, as least in one study it was not identified as a culprit but as an unindicted co-conspirator.
Estrogen is a different topic. The article found no increase in estradiol levels (i.e., estrogen) between the two groups and found a LOWER level of estradiol in the 2006-2008 population of 8-10 year old girls.
Here's the puzzle. Weight is NOT a causal factor. Estrogen levels are not increasing and may be decreasing. Yet, breast development stage 2 is occurring earlier. It is precisely this puzzle that the new US study is trying to address.
A plausible hypothesis is that environmental estrogens in our food somehow cause the earlier onset. First, you need to understand how environmental estrogens work. Many women who reach the age of menopause try to eat more soy and take naturally estrogenic foods and supplements (phytoestrogens). These are weak estrogens that stimulate the estrogen receptor in the absence of naturally produced estrogen. In a young girl, a similar situation would exist. In an older woman's body, the estrogen receptors have been acclimated to a high level of estrogen. The use of phytoestrogens may be helpful but may not be powerful enough to achieve the desired effect. However, in a young girl whose body is just beginning (or may not be ready) for an influx of estrogen, the phytoestrogens may represent a much stronger signal than in an older woman. Add to this information the class of suspected environmental estrogens, and you have a rich brew that is worthy of further research to see if phytoestrogens and environmental estrogens are the ultimate culprits.
This is exactly what the authors of the new US Study hope to examine in the future. As I understand the press releases, the authors have collected blood samples from the girls for analysis of environmental estrogens. This will not tell us if environmental estrogens are the ultimate culprits, but it will go a long way to narrowing some of the unknowns.
What's the bottom-line? The usual. Watch what your children eat. Try to eat a more organic diet. Moderate your family's intake of soy products and other phytoestrogens. Stop buying products that you feel are manufactured or packaged in a way that increases the risk to your family, e.g. the whole unresolved BPA issue. Make smart decisions, but accept the reality: Each action may be rational, but none may be the ultimate cause of the problem.
To be continued.