Early puberty for girls. The new ‘normal’ and why we need to be concerned

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Review Essay

Many of us have heard the anecdotal evidence and may even know someone—a neighbour, a niece, a daughter: girls with breast buds and pubic hair at age 6 or 7 and first menstruation for 8-year-olds becoming the norm, not the exception.  

In The Falling Age of Puberty in US Girls (2007), Sandra Steingraber, who is probably best known for her groundbreaking work on the links between environmental health contaminants and cancer, undertakes a thorough meta-analysis of the existing data on early puberty in girls. She carefully traces the complex and interlocking relationships between puberty, which includes the advent of breast buds, pubic hair and menarche (first menstruation), with physiological, psychological and environmental (nutritional, chemical) conditions, and the consequences for the maturation process of our young women.

The impetus for Steingraber’s meta-analysis may surprise some: breast cancer. While many of us may think of breast cancer as a tragedy far removed from the early years of puberty, research now indicates that early menarche is a known risk factor for breast cancer developed later in life. Thus, the Breast Cancer Fund commissioned Steingraber to undertake an analysis of declining puberty age rates to help trace the neuro-hormonal mechanisms that govern breast development in its earliest stages, and to find what may influence and trigger this earlier growth.

What Steingraber uncovers is not simply a series of cause and effect operations in pubertal development, but interwoven and interdependent systems with complex variables that make it extremely difficult to trace cause from effect.

Turning puberty on in America

According to Steingraber, a simple definition of “puberty” for girls can be stated succinctly as the “attainment of fertility,” but of course this includes many important neural and hormonally triggered developmental milestones, including a significant growth spurt, breast development (thelarche), pubic hair (pubarche) and first menstruation and ovulation.

What is remarkable about puberty is how little we still know about it; while we know the basic neural and hormonal pathways that must interact to initiate the processes involved in puberty development, there is no predetermined onset nor is the length of the process itself predetermined; timing (commencement and duration) may vary widely from person to person and is influenced by a wide range of environmental factors and cues that are not entirely known. “Normal” puberty onset can range from ages 8-13 years of age and may take, on average, 1.5 to 6 years to complete. 

Steingraber reveals that good documentation exists over the last hundred or so years to establish that the average age of first menstruation in young white girls in the United States has declined by several years, from an average age of 17 to 13. Over the last 50 or so years, the age of first menstruation in the United States has continued to decline, but at a much slower—by a few months, and with wide ethnic disparity.

Small cohort studies indicate that Canadian data are comparable. According to Professor Diane Francœur, specialist in Obstetrics and Gynecology at the University of Montreal, the Canadian pattern is similar, though no wide-ranging, Canadian-specific studies have yet been completed.

White girls in the United States now menstruate at an average age of 12.6 years and black girls at 12.1 years, while Mexican American girls menstruate at an average age of 12.2 years (though it is not clear how far these differences in menarche can be traced back, since most of the historical documentation focuses on white American and European girls). 

What is more difficult to determine historically due to the dearth of information, Steingraber demonstrates, are the changes in the earlier signs of pubertal development, such as the onset age of breast budding and of pubarche. However, data from the last few decades have shown a dramatic decline in the onset age for both breast budding and pubarche and these rates are continuing to decline significantly (unlike menarche onset which has appeared to plateau).

To put this into context, Steingraber says, “girls get their first periods, on average, a few months earlier than girls 40 years ago, but they get their breasts one to two years earlier.”

Fifty percent of white girls in the United States now show signs of breast budding before their 10th birthday with as many as 14% showing breast development by the age of 8; average age of breast budding for black girls in the United States is just under 9 years of age with a significant percentage of thelarche development before age 8.

As Steingraber concludes, “It is now the opinion of most endocrinologists...that the falling age of puberty among US girls is a real and ongoing phenomenon.”  What is not as clear is why this is happening, and what (or if something) needs to be done about it.

Chemical cocktails and the new “normal”

Most experts, including Steingraber, agree that the early decline in the age of puberty is likely directly attributable to decreased rates of disease and increased nutrition, and the ability of human females to adapt their sexual maturation to environmental cues (e.g., health, food and shelter). This is why it is difficult to speak of a “normal” age and time for puberty. We are adaptive creatures, so “normal” is always changeable: dependent upon our environmental (personal and communal) conditions.

Implicit in Steingraber’s assessment is that this also means that “normal” rates of puberty development are not necessarily “good” or “healthy” either (as the word “normal” often implies): it is simply an average marker of response to external circumstances which impact internal functions.

Steingraber argues that more recently, particularly in the last several decades, trends in the decline of the onsetof puberty in the United States (which are similar with other affluent countries or countries with similar ethnic heritage) seem to be responding to stimuli beyond nutrition and general health.

Her report highlights numerous studies which have linked exposure to chemicals in our environment, particularly endocrine-disrupting chemicals (which can mimic hormones in the body), to a plethora of health concerns, such as shortened gestational periods in fetal development, low birth weight babies, higher rates of obesity and poor insulin regulation in the body, which are all risk factors for early puberty. This should make us sit up and take notice, since as Steingraber says, “children are exposed continuously to low-level endocrine disruptors in their diets, drinking water and air supply.” 

Chemical flame retardants, for example, polybrominated biphenyls (PBBs) have been linked to earlier menstruation in girls and with earlier pubarche. Similarly, high levels of dioxin exposure have been associated with elevated risks for breast cancer and early menarche.

Also, hormonally active components, which have been linked to earlier pubertal development, can be found in a wide array of consumer products, including hair tonics, pesticides, packaging and building materials.

As a result, studies have shown hormonally active agents in the urine of US girls and traces of such known human contaminants as phthalates and bisphenol A (which was originally developed as a synthetic hormone, but is now used in all polycarbonate plastics and the linings of food and beverage cans, among other uses; it has been recently been banned in Canada for use in baby bottles). Rat studies on bisphenol A indicate that prenatal and early-life exposure can induce earlier sexual maturity.

The use of natural and synthetic hormones to promote growth in US livestock and stimulate milk production in dairy cattle (a practice banned in European countries) has also raised concern; critics of the practice believe this may contribute to early puberty onset, but again, more research is necessary.

Steingraber concludes that, in combination, this chemical cocktail may be a significant factor in causing the “new normal” rates of pubertal development in US girls, but we don’t have enough research to say for certain—only enough research to raise red flags and caution.

And we also need to know how these chemical contaminants act and combine with other known risks for earlier puberty development, such as smoking, obesity, physical inactivity and psychosocial stressors (e.g., family dysfunction), to contribute to early puberty onset, and what other physical consequences this may have for human development.

The loss of childhood

In addition to the increased risk for breast cancer as a result of earlier puberty onset, and the other effects of chemical contaminants on human development, Steingraber makes clear in her assessment that there are also many social reasons why we should be concerned about the declining age of puberty.

While one may argue that as puberty declines, we may need to separate our notions of “childhood” from physiological development (an 8-year-old with breasts is no less a child than an 8-year-old who has not yet developed), society nevertheless projects a multitude of pressures on young girls who mature at an early age.

Steingraber details a variety of studies that show that girls who enter puberty earlier report more anxiety, negative self-images and suicide attempts; they are also more likely to abuse drugs, take up cigarette smoking and drink alcohol than their counterparts.

Girls who have early pubertal development are also more likely to be on the receiving end of physical and sexual violence. On the whole, they have lower levels of academic achievement and a higher and earlier level of sexual activity. They are also more likely to have a teenage pregnancy.

Early maturing boys do not have these same behavioural patterns or outcomes. As Steingraber says, it may be that “early puberty alters a girl’s social interactions in ways that produce trauma and erode self-esteem.” 

What we need to do

Steingraber’s exhaustive analysis in The Falling age of Puberty in US Girls is a tribute to her ability to integrate biomedical knowledge with environmental and chemical research and social and cultural determinants and consequences. This is no simple endeavor.

What is striking is our continued lack of information on the chemicals in our environment and the consequences they may have on human health; this is combined with our tendency to view human bodies (and processes) independent of their environmental conditions and surroundings, when only a more integrated approach will bring us the answers (or raise the proper questions) we need.

In particular, Steingraber believes that we need to routinely screen for endocrine-disrupting chemicals and hormonally active agents in our environment (air, water and food) and monitor the effects these chemicals have on infants, children and adults and their development.

But more importantly, we need to study the potential damaging effects of chemicals on human and environmental health, singly and in combination, prior to their mass use in consumer and other products. Governments also need to regulate more stringently the use and release of these chemicals into our environment.

According to Kathleen Cooper, Senior Researcher at the Canadian Environmental Law Association, in the absence of comparable population health data on puberty rates in Canada, but given our similar industrial trends, we can probably expect a similar pattern in Canada as in the United States. She adds that “as part of a bigger need for environmental health research, particularly in the early years, we should be investigating whether the age at menarche is declining in Canada, and if so, investigate the possible contribution of substances suspected of endocrine disruption here, especially those in common consumer products.”

What Steingraber’s report effectively concludes is that the trigger for early puberty development in girls—which is real and should be a cause for concern—is not a simple single cause with effect, but an intermingling web of causal factors that initiate multiple 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 environments (our water, food and air) and our physical and social development. Our evolution may depend on it.

Kathleen O’Grady is the co-author of Sweet Secrets: Stories of Menstruation (Sumach Press) and a Research Associate at the Simone de Beauvoir Institute.