The jury is still out on just why young people are experiencing puberty earlier than ever, and experts are now calling for a better understanding of the causes, and what it might mean for health.
In the 1860s in Europe, the average age at which girls got their first period was around 16 years, six months. By 1950, the age was just older than 13 years, reports The Lancet.
In dozens of countries, the age of puberty in girls, which is marked by the onset of breast development, has dropped by about three months per decade since the 1970s, according to a 2020 systematic review. Several studies have also documented a trend towards earlier puberty among boys in some countries, a trend, that while less pronounced than in girls, has been more profound among minority ethnic groups.
Whether these trends will continue is unknown.
One long-running study of 1 000 young people in Melbourne, Australia, suggests that the timing of puberty has stabilised in predominantly white populations over the past few decades. However, regardless of what the future holds, researchers are urging an examination of how structural factors influence puberty and menstrual health and the potential health implications.
One study by researchers at Harvard TH Chan School of Public Health examined trends – over 55 years – in age at first period and time to cycle regularity in 70 000 females. They found that the trend towards earlier periods across all demographics existed and, on average, menstruation began at age 11 years, nine months in 2000-05, with the proportion of girls getting their period before 11 in 2000-2005 being almost double the proportion in 1950-1969.
However, this trend was more pronounced among girls from racial and ethnic minorities and those from lower incomes. Researchers found that BMI at the age of the first period could explain part of the trend towards periods starting earlier.
While numerous studies have established that girls who are overweight or with obesity often start their periods earlier than girls of average weight do, several experts believe this explains only part of the effect.
“While BMI is one potential driving factor that we evaluated, we need to look more into other factors that may be causing earlier age of first period/taking longer to establish regular periods,” said Zifan Wang, a postdoctoral research fellow at Harvard Chan School's Department of Environmental Health and one of the authors of the study.
“These factors may include what’s in the environment – like chemicals that affect hormones, or air pollution, dietary patterns such as the increased consumption of sugar-sweetened beverages, stress and adverse childhood experiences. Studying these factors could help us find better ways to stop or slow down these trends.”
The Covid-19 pandemic saw an increase in early puberty worldwide, where more girls attended clinics with physical pubertal signs before the age of eight. Several studies suggested psychosocial and environmental factors were involved, including weight gain.
One study in Italy found that 328 girls were referred to clinics across the country for early puberty in 2020, compared with 140 during the same period in 2019. No difference was found in boys.
The study cited the prolonged use of electronic devices, decreased physical activity and stress as possible drivers.
Lauren Houghton, an assistant professor of Epidemiology at Colombia University, told The Lancet that stress and exposure to endocrine-disrupting chemicals could have a role in earlier periods, along with other factors, all of which are “much harder to measure and study”.
“If we have broken food systems, unsafe neighbourhoods that restrict physical activity, damaging social media causing internalised stress, racially-targeted advertising of personal care products which have harmful chemicals, then it is not a surprise that the average age of menarche is now reflecting an unhealthy society,” she said.
“Many people overly attribute declining age of menarche to rising rates of obesity (but) obesity is only one driver.” Anders Juul, a paediatric endocrinologist and clinical professor at the University of Copenhagen, said that exposure to endocrine-disrupting chemicals in combination with increasing fat mass was likely to be affecting the “worrying trend towards earlier puberty”.
“Environmental chemicals with hormone-like activities may promote the premature activation of the pituitary-gonadal hormone axis, resulting in pubertal development and/or act directly to stimulate the breast gland with oestrogenic or anti-androgenic activity,” he said.
However, in a recent meta-analysis in which Juul and colleagues analysed hundreds of studies looking at endocrine disrupters and their effects on puberty, they were unable to show a clear association between any individual chemical and the age of puberty.
“Studies are difficult to compare, so more studies are required,” he said. Wang expressed concern about the health implications of early periods or longer time to regulate cycles on adolescents later in life, including diabetes, cardiovascular disease, infertility, polycystic ovary syndrome, pregnancy complications, and breast and uterine cancer.
Likewise, Houghton was concered about the health implications of not only early age at menarche but early age at breast development, both of which, she said, are associated with a 20%-30% increased risk of breast cancer.
Breast screening programmes do not usually begin until the age of 40. She anticipates a higher incidence of early-onset breast cancer.
“What is most worrying about these trends is how menstrual stigma and biology intersect to worsen gaps in health outcomes between women and men,” Houghton said. “If there are more youth beginning puberty earlier, are we adequately equipping them with the tools they need to know their bodies and to manage it?
“Are we educating their non-menstruating peers so that their generation can come of age in a culture with less stigma around menstruation? Society needs to support menstruation as a vital sign across the life course so that these young women understand their bodies and are empowered to voice their concerns.
“Likewise, policy makers need to create health systems that are ready to receive, treat, and not dismiss, menstrual health-related problems.”
Regardless of when puberty begins, the transition from childhood to adulthood is accompanied by an increase in mental health disorders, including depression and anxiety.
In a recent study, Nandita Vijayakumar (a cognitive neuroscientist at Deakin University in Geelong, Australia, and the Murdoch Children’s Research Institute) and colleagues compared brain scans of girls who started puberty early with those who started puberty later.
During adolescence, those who started puberty earlier had, on average, less connectivity between their prefrontal cortex and the amygdala in the brain. “We found that kids who were early developers had a differential pattern of this functional connectivity and that this pattern went on to predict future mental health problems,” Vijayakumar told The Lancet, adding that this connection was vital for emotional processing and reactivity.
The brain connectivity changes, the study found, were related to increased risk of depression, a hypothesis that requires further investigation.
“It’s important to keep in mind that not who goes through early puberty will have mental health problems. Family environments, neighbourhood characteristics and peer experiences might all increase the risk. We need to try to understand the different pathways through social contexts, factors that we can change.”
Beyond neuroscience, Vijayakumar hopes to see research examine the impact of social media on the development of early puberty and explore how sexual and gender minority children experience early puberty and its impact on mental health.
Houghton would like to see a multi-level intervention that provides sexual health literacy, access to healthy food, and improved medical systems, and which would recognise that structural factors can interfere with menstrual health and be modified.
Similarly, Wang wants greater investment in early counselling, education around menstrual health as a vital sign, and individualised healthcare plans. If menstrual health is an indicator of overall health, then considering it as the fifth vital sign could not only raise the importance of understanding menstrual health and its influences but could also help tailor medical care to individual needs.
The Lancet article – The great puberty shift (Open access)
See more from MedicalBrief archives:
Health concerns as girls reach puberty earlier than ever
Adolescence ‘now lasts from ages 10-24’
Early menstruation linked to sugar in drinks