Girls seem to experience puberty at a younger age than they used to.
From the 1990s onwards, researchers started with documentation That girls started developing breasts around the age of 10, more than a year earlier than has been recorded in the previous medical literature. The same study found that black girls hit puberty even earlier, averaging around age nine.
This was not a one-off study. Researchers began tracking the trend in countries around the world over the next few decades, and that research points to a global trend. In many countries, the puberty age for girls seems to have decreased by about three months per decade since the 1970s. The same trend was seen in boys, but it’s less dramatic.
Early puberty in girls is associated with an increased risk of anxiety, depression, substance abuse and other problems compared to those who reach puberty later. It has also been linked to some cancers when menstruation starts earlier than others.
It’s difficult to give a definitive answer as to why this happens, but researchers have identified three factors that likely contribute to the problem: body weight, stress and exposure to certain chemicals.
Obesity is an important factor, and this has been shown in several studies. One theory is that fat cells are known to produce a variety of hormones, some of which can activate the body processes that stimulate the onset of puberty. Fat cells are not necessarily bad, and this is part of a normal healthy growth process. However, it can be a problem when girls accumulate a lot of body fat at a young age, but researchers think this cannot be the complete explanation, as many girls start early puberty who are not overweight.
Another possibility could be chemicals. a 2009 study study Of the nearly 1,000 young girls in Copenhagen who found that the mean age of puberty for breast tissue in the girls group as of 2006 was much earlier than in 1991. The 2006 group had started puberty more than a year earlier than their 1991 peers.
The doctor behind that study hypothesized that chemicals could be part of the change. The girls with early breast development in the study also had the highest levels of phthalates, he said in their urine. Phthalates are found in many plastics and in some hair products, and have long been on researchers’ radar because they can be harmful.
Phthalates are part of a larger group of chemicals known as ‘endocrine disruptors’, which can also affect hormones. Although several studies have looked at this, they have struggled to establish a definitive link between certain chemicals and precocious puberty.
There is some preliminary evidence that girls who have been sexually abused early in life are at increased risk in early puberty, but a causal relationship is difficult to prove.
The researchers also identified some other interesting associations. For example, it is more common for a girl to reach early puberty if her mother has a history of mood disorders, or if she does not live with her biological father. Again, causation is difficult to prove, but lingering tension may be the common factor.
An interesting study that points to stress is an Italian study published in February. It looked at the number of children with suspected precocious puberty in five pediatric endocrinology offices in Italy in 2020, compared to 2019. The study found that only 140 girls had symptoms of precocious puberty in 2019, compared to 328 in 2020. The number of girls with these symptoms will more than double by 2020. Researchers have also identified a link between assertive precocious puberty in girls and a sedentary lifestyle, as well as increased use of electronic devices.