Girls are entering puberty a year earlier than their mothers’ generation

The first signs of puberty are showing themselves earlier. Gradually, the age when children’s bodies start to undergo these changes is getting lower and lower: girls of this generation are starting to experience thelarche or breast-budding, the first sign of puberty, a year earlier than their mothers did, according to an international study published in the scientific journal Jama Pediatrics. The researchers found that thelarche has been advancing by an average of three months a decade since the late 1970s and they point to obesity and endocrine disruptors as the probable causes of this trend. Menstruation, a sign of puberty having been completed, is also gradually arriving sooner, although not nearly as rapidly, say sources consulted for this story. Experts are warning of long-term health risks if puberty continues to start earlier.

This transitory stage between childhood and adulthood begins, according to scientific consensus, with the first signs of puberty, such as thelarche in girls and testicular growth in boys, which tends to start at the age of 10 in the latter case and around the age of nine in the former, according to Raquel Corripio, spokesperson for the Spanish Society of Pediatric Endocrinology. “Between the ages of nine and 13, 99% of girls show some sign of pubertal change. It is equally normal for this to occur at age nine, 10 or 11.” However, before the age of eight (or nine in the case of boys) is considered premature puberty and it requires medical consultation to determine if treatment is needed.

But when the scientific community talks about an earlier start of this vital stage of growth, they are not referring to premature puberty as such, but rather pointing to the fact that this transition from childhood to adulthood - although still within the canons of normality – is beginning ever earlier, says Manuel Tena, head of the Spanish Biomedical Research Centre in Physiopathology of Obesity and Nutrition. “These are not cases of premature puberty. It is an epidemiological problem: we are talking about the fact that, from a population point of view, the age of onset of breast development in girls is being brought forward.”

Anders Juul, author of the Jama Pediatrics study and head of the Department of Growth and Reproduction at the Rigshospitalet in Copenhagen, notes that an article published in 2009 already highlighted this trend. “In Copenhagen we discovered that the average age of breast development had decreased from 11 years in 1991 to 9.9 years in 2006,” he says. The new scientific review, based on an analysis of around 30 studies, calculates that the age of thelarche onset has dropped by around three months per decade. In terms of menstruation, Juul says that even though “there is a tendency toward an earlier age,” this is “less marked in comparison to the trend in breast development.”

According to Tena, science is witnessing “a disassociation between the start and end of puberty.” There is a kind of “distortion” in the natural progression of the beginning of this transitory phase, which generally starts with thelarche in girls – although sometimes the appearance of pubic and axillary hair is also seen – and ends, around two years later, with the appearance of a first period. “Today, girls are entering puberty earlier but they are not menstruating earlier. The space of puberty is widening: there is a widening of the pubertal performance period.”

In the case of boys there is more controversy. Earlier onset of puberty has also been witnessed but it has been less studied to date, says Corripio. “It appears that in boys the onset of puberty is becoming more advanced. But it has not been studied and demonstrated to the same extent because there are fewer cases and it is more difficult to measure testicular growth indicators.” Boys are considered to have entered puberty when testicular size exceeds four milliliters. Tena agrees that it may be under-diagnosed “because testicular growth is difficult to see” and also because greater exposure to estrogenic factors may have more effect on boys.

Risk factors

In girls, experts point to several factors as causes for this trend. There are no absolute certainties, but all agree that obesity is a key element: there is a correlation between girls with a higher body mass index (BMI) and earlier onset of menarche (the first menstrual cycle) and thelarche. Sudden weight gain is enough to trigger early onset of puberty, says Lourdes Ibáñez, head of endocrinological clinical research at the Sant Joan de Déu Children’s Hospital in Barcelona. An increase in BMI that involves a change in the percentile at birth can trigger a response. “We are not talking about being obese. A weight gain of three kilos in a month can be enough,” she says.

Tena concurs and warns that “a rapid change in weight near puberty can be as decisive as sustained obesity.” A key factor could be leptin, a hormone that is produced in adipose cells and acts as a signal to the brain that there are sufficient energy reserves for the beginning of the reproductive age to commence. “With weight gain, there is an increase in leptin levels, which tell the brain there is enough critical fat mass for puberty to begin. That’s why in very thin girls, who have low leptin levels, this phase is delayed.”

Juul maintains though that if girls who are carrying more weight reach puberty faster, “it is likely that other causes are involved.” The Rigshospitalet researcher points to endocrine disruptors, chemical substances that are found in many plastics and that imitate hormones within the body. “High levels of phthalates have been found to be associated with the early onset of puberty, but firm general conclusions cannot be drawn by studies on humans,” he says. The review published in Jama Pediatrics also notes that some chemicals, such as DDT (dichlorodiphenyltrichloroethane) and DDE (dichlorodiphenyldichloroethylene) have also been associated with early puberty.

Experts also point to a third factor: mental health. Ibáñez says that the hypothalamus – the area of the brain that secretes gonadotropin hormones, which are key to the development of puberty – “is very sensitive to stress and this can lead to the onset of puberty or inhibit ovulation.” Corripio states that adoption is also a risk factor for the early onset of puberty. Another US study found a link between exposure to childhood sexual abuse and earlier puberty.

Tena notes that the impact of mental health “is not as well characterized as the role of leptin,” but he adds that he has seen that “pubertal activation accelerates in girls from single-parent families.” Juul agrees: “Socioeconomic factors are important. Stress during infancy can play a role: the absence of a parent is associated with early puberty in the child.” In children whose parents have divorced, a study also found that menstruation begins earlier. Another investigation among children in Srebrenica, the scene of a genocidal massacre in July 1995, during the Bosnian War, found that the age of menarche was higher than in the control group, which was made up of children who lived in areas that were not as affected by the conflict. The researchers concluded that “psychological traumas, physical injuries and a low socioeconomic level, brought about by the events of the war, delay the onset of menarche.”

Health impacts

In any case, the earlier onset of puberty carries health implications. Juul says that it “can cause psychosocial distress and loneliness. The long-term effects of early puberty include a greater risk of metabolic syndrome and breast cancer.” A study published in Breast Cancer Research concludes: “The development of the breast ducts may be a moment in which there is increased risk of carcinogenesis, and greater attention needs to be paid to the relationship between the risk of breast cancer and the different stages of puberty.”

Tena highlights other risks, such as short stature, cardiovascular and metabolic ailments or gynecological problems as well as more psychological and psychiatric issues “due to the disassociation between physical and psychological maturity.”

Despite negative effects on health, experts believe that early puberty does not require any medical intervention, at least not in the case of premature puberty, for which there is an intramuscular treatment available to inhibit the hormones that drive the beginning of puberty. “What is the solution? Avoiding all of the factors that lead to it, such as obesity,” says Tena.