If it seems like girls these days are hitting puberty earlier than in decades past, you're not imagining things—and researchers now suggest obesity and environmental chemicals may be playing a role. The Guardian reports on new research out of the University of Copenhagen that looked at 30 global studies on thelarche, which is the beginning of the development of glandular breast tissue, widely seen as the first sign of puberty's onset. Scientists found, per the research published in the Feb. 10 edition of JAMA Pediatrics, that puberty in girls has started about three months earlier per decade from 1977 to 2013—meaning girls today are heading into puberty about a year earlier than their '70s counterparts.
The researchers also found this early breast-tissue development varies around the world, and over time: The average age of onset in the US is 8.8 to 10.3 years, while in Europe it's between 9.8 and 10.8 years, and in Africa 10.1 to 13.2 years. How this affects girls in the long term isn't clear, though study co-author Alexander Busch notes an early arrival of the final clinical sign of puberty, menstrual bleeding, has been tied to an increased risk of Type 2 diabetes, heart disease, and obesity, per HealthDay. The latter may even be partly responsible for puberty's early call: The researchers note a higher BMI has been associated with an earlier menstruation kickoff, while chemicals in the environment like DDT and DDE have also been linked to earlier puberty. More research is needed, the scientists say, as "a younger age at pubertal onset may change current diagnostic decision-making." (Read more puberty stories.)