Lancet
Why are girls entering puberty earlier than ever?
Obesity is one driver to the dropping age of puberty onset, but it may not be the only one—environmental chemicals may also play a role, according to this report about relevant studies. The age of menarche in the 1860s was approximately 16.5 years in Europe; by 1950 it had dropped to just over 13 years; and in the U.S., down to 11.75 years by the early 2000s. Around the world during the COVID-19 pandemic, more girls younger than 8 years old presented to clinics with signs of puberty compared with the past. A 2020 systematic review across multiple countries showed that breast development onset has dropped by about 3 months for every decade since the 1970s.
Obesity as a driver. Researchers at Harvard’s Chan School of Public Health analyzed trends in menarche age and time to cycle regularity in 70,000 females, spanning more than half a century. A trend of earlier periods was seen across all demographics: in 2000–2005, menstruation began at an average age of 11 years, 9 months. The proportion of girls with first period under age 11 years in 2000-2005 was almost double the proportion in 1950-1969. The trend was more pronounced in ethnic minority groups and those with lower household incomes. However, BMI at menarche explained only part of the trend.
Potential environmental factors. Environmental chemicals, including from air pollution, may possess hormone-like properties that may activate the pituitary-gonadal axis prematurely. This activation could result in estrogenic or anti-androgenic stimulation of breast tissue. However, one meta-analysis of studies examining endocrine disruptors failed to demonstrate an association between individual chemicals and pubertal onset. Researchers reported that these chemicals are challenging to measure and study.
Health implications. Early menarche and early age of breast development may influence overall breast cancer risk. Stigma about menstruation may also be an issue for young girls. Educators are encouraged to view menstruation as a “vital sign” throughout the course of life.
Source:
Cousins, S. (2024, August 10). Lancet. The great puberty shift. https://pubmed.ncbi.nlm.nih.gov/39128480/