It seems that girls are experiencing puberty at a younger age than in the past.
From the 90s, researchers began document that girls began developing breasts around the age of 10, which was more than a year earlier than had been recorded in the previous medical literature. The same study found that black girls started puberty even earlier, on average around the age of 9.
This study was not an isolated case. Researchers began observing the trend in countries around the world over the following decades, and these research findings suggest a global trend. In many countries, the age of puberty for girls appears to have declined by about three months every decade since the 1970s. The same trend was seen in boys, but less dramatically.
Early puberty in girls is associated with an increased risk of anxiety, depression, substance abuse and other problems compared to those who hit puberty later. It has also been linked to some cancers if they start menstruating earlier than others.
A definitive answer as to why this happens is difficult to determine, but researchers have identified three factors that likely contribute to the problem: body weight, stress, and exposure to certain chemicals.
Obesity is a major factor and this has been shown in various studies. One theory holds that fat cells are known to produce a variety of hormones, some of which can trigger bodily processes that stimulate the onset of puberty. Fat cells are not inherently bad, and this is part of a normal, healthy developmental process. However, it can be a problem when girls accumulate a lot of body fat at a young age, but researchers believe this may not be the full explanation because many girls who are not overweight hit puberty early.
Another possibility could be chemicals. A Study 2009 of nearly 1,000 young girls in Copenhagen discovered that the average age for breast tissue formation was much earlier in the 2006 group of girls compared to 1991. The 2006 cohort entered puberty more than a year earlier than their 1991 counterparts.
The doctor behind this study hypothesized that chemicals could be part of the change. He said the girls with the earliest breast development in the study also had the highest levels of phthalates in their urine. Found in many plastics and some hair products, phthalates have long been on researchers’ radar as potentially harmful.
Phthalates belong to a larger group of chemicals known as “endocrine disruptors” that can also affect hormones. Although various studies have looked at it, they have had difficulty establishing a definitive link between certain chemicals and early puberty.
There is some preliminary evidence that girls who experience sexual abuse early in life are at increased risk of earlier puberty, but establishing a causal link is difficult.
Researchers have also identified some other interesting correlations. For example, it’s more common for a girl to hit puberty early if her mother has mood disorders or if she doesn’t live with her birth father. Again, it’s difficult to establish causality, but ongoing stress may be the common factor.
A very interesting study implying stress is an Italian study published in February. She analyzed the number of children presenting with suspected precocious puberty at five pediatric endocrinology practices in Italy in 2020 compared to 2019. The study found that in 2019 only 140 girls had symptoms of precocious puberty, compared to 328 in 2020. The number of girls with these symptoms more than doubled in 2020. Researchers also found a link between confirmed precocious puberty in girls and a sedentary lifestyle and greater use of electronic devices.