Girls are entering puberty much younger than before, causing a myriad of problems. Why is this happening, and what does it mean?
Most endocrinologists in North America agree that girls begin to menstruate at a younger age than in decades past. What is not as clear – and the subject of much debate – is why this is happening, and what – if anything – needs to be done about it.
Over the last 100 years, the average age of first menstruation for young white girls in the U.S. has declined from 17 to 13 years old, a drop that has significantly slowed over the last 50 years.
There is also wide ethnic disparity. White girls in the U.S. now menstruate at the average age of 12.6 years, black girls at 12.1 years, and Mexican American girls at 12.2 years. Small cohort studies indicate that Canadian data are comparable.
What is more difficult to determine are historical changes in the earlier signs of puberty, such as the appearance of breasts and pubic hair, though the available data demonstrates a dramatic and continuing decline in the onset age for both (unlike the onset of menstruation which has appeared to plateau).
Half of America’s white girls now show signs of breast budding before their 10th birthday, with as many as 14 per cent showing breast development by the age of 8. The average age of breast budding for black girls in the U.S. is just under 9 years of age, with a significant percentage under the age of 8.
In other words, while first menstruation may be happening a few months sooner compared to 20 or 30 years ago, the development of breasts and pubic hair is happening one to two years earlier.
The change has many health experts and advocates sounding the alarm.
**Turning puberty on in America**
The early decline in the age of puberty, most agree, is likely attributable to less disease and more nutrition, because the sexual maturation of girls adapts to environmental cues.
This is why it is difficult to speak of a “normal” age for puberty. Because we are adaptive creatures, “normal” depends on our environment (both personal and communal). But this can also mean that “normal” rates of puberty development are not necessarily “good” or “healthy.”
In her meta-analysis ["The Falling Age of Puberty in U.S. Girls"](http://www.breastcancerfund.org/site/pp.asp?c=kwKXLdPaE&b=3266489 ), Sandra Steingraber argues that recent trends in the falling age of the onset of puberty in the U.S. (which are similar to countries of comparable affluence or ethnic heritage) seem to be responding to stimuli beyond nutrition and general health.
Her report highlights numerous studies that have linked exposure to chemicals in our environment – particularly endocrine-disrupting chemicals that can mimic hormones in the body – to a plethora of health concerns, including shortened gestational periods in infant development, babies with a low birth weight, higher rates of obesity and poor insulin regulation in the body, which are all risk factors for early puberty.
Other studies have linked chemical flame-retardants to earlier signs of puberty in girls. Similarly, high levels of dioxin exposure have been associated with elevated risks for breast cancer and early menstruation.
Hormonally active agents, which have been linked to earlier pubertal development, can be found in a wide array of consumer products, including hair tonics, pesticides, food packaging, and building materials. Studies have found such agents in the urine of U.S. girls.
The use of natural and synthetic hormones to promote growth in U.S. livestock and stimulate milk production in dairy cattle (a practice banned in Canada and the European Union) has also raised concern. Critics of the practice believe that it may also be contributing to the early onset of puberty.
Exposure to this chemical cocktail may be a significant factor in causing the “new normal” rates of pubertal development in girls, but there isn’t enough research to say for certain. Still, the data are enough to raise red flags.
**The loss of childhood**
Why does it matter in any case? Why should earlier puberty in girls be a subject of concern and study?
Firstly, there are physiological concerns. Research indicates that an early start of menstruation is a risk factor for breast cancer later in life.
Secondly, there are also sociological concerns. A variety of good studies show that girls who enter puberty earlier report more anxiety, negative self-images, and suicide attempts. They are also more likely to abuse drugs, smoke cigarettes, and drink alcohol than their counterparts. Girls who have early pubertal development are also more likely to be the victims of physical and sexual violence.
On the whole, they have lower levels of academic achievement and an earlier and higher level of sexual activity with a greater chance of having a teenage pregnancy. It is interesting to note that early maturing boys do not have the same behavioural patterns or outcomes.
**What we need to do**
In Canada, there is a dearth of research on environmental health. Forthcoming studies from the federal government’s [Chemicals Management Plan](http://www.chemicalsubstanceschimiques.gc.ca/plan/index_e.html) – including national biomonitoring and surveillance through the Canadian Health Measures Survey, Maternal-Infant Research on Environmental Chemicals, and the Northern Contaminants Project – are welcome, but do not go far enough.
None of these initiatives plan to focus on the declining age of puberty of Canadian girls to establish if trends in America are mirrored here. We need, at the very least, a baseline to track trends over time and allow for comparisons with sub-populations (both within and beyond our borders).
We also need data to explore the relationship between environmental chemicals and early puberty. We need to routinely screen for endocrine-disrupting chemicals and hormonally active agents in our environment, and monitor the effects these chemicals have on infants, children, and adults.
What research we do have reveals that the trigger for early puberty development in girls does not have a single cause. Rather, there is an intermingling web of causal factors that initiate multiple physiological changes and set the stage for other responses.
To unravel all of this, we need to begin, in earnest, to appreciate the interplay between the chemical burden in our environment and our physical and social development. Our evolution may depend on it.