A new study of over 70,000 women born between 1950 and 2005 has shown that girls are getting their periods earlier and they’re taking longer to become regular.
While the average age reduced by a relatively small amount, the percentage of girls whose first period would be classified as ‘early’ or ‘very early’ has nearly doubled.
Over 71,000 American women with an iPhone were asked to remember the age at which they had their first period (menarche) and how long it took before their cycles regulated.
The women were categorised by year of birth, self-reported ethnicity and self-reported level of deprivation, revealing that from 1950s/1960s up to early 2000s, the age of first period decreased from on average 12.5 years old to 11.9 years old.
Most women had their cycles regulate within 1-2 years (which is considered the ‘norm’), but a higher proportion of the younger women in the study took more than two years compared to the older women.
Lead author Dr Zifan Wang from Harvard University’s Chan School of Public Health, explained that as early periods were strongly linked to poorer health outcomes later in life, it was essential to understand the underlying causes.
“Onset of menarche is closely related to attainment of adequate body fat via pathways such as increased insulin-like growth factor 1 and leptin that stimulate gonadotropin-releasing hormone,” Dr Wang said.
“In our exploratory analysis, we found that BMI at menarche may explain 46% of the temporal trends in menarche. This finding suggests that childhood obesity, which has increased in the US, is a risk factor for earlier puberty and could be a contributing factor to the trend toward earlier menarche.”
While a higher body mass index could explain about half of the early start times observed in the study, stress, poor nutrition, and environmental pollution could also be playing a role.
Associate Professor Michelle Wise, from the Department of Obstetrics and Gynaecology at the University of Auckland highlighted the potential impact of socio-economic disadvantage on early menarche, noting that the age reduction was more pronounced for dark-skinned women than pale-skinned women, and for women in more deprived areas than better-off women.
“I suspect we would see similar results here in Australia and NZ as we, like the United States, are high-income countries,” she said.
“In my practice as a gynaecologist in a large public hospital, we see many women every day with irregular menstrual cycles, and our routine questioning includes age of menarche and how long it took for cycles to become regular.
“We see heavy menstrual bleeding resulting in anaemia and poor quality of life, new diagnoses of endometrial cancer in women in their 30s and 40s, and couples having difficulty conceiving.
“However, we would have to do a similar survey using our ethnicity and socioeconomic mix, otherwise it is difficult to know if we too would see similar variations in age of menarche over time.”
Associate Professor Wise also pointed out that local research was scant.
“For example, a prospective longitudinal cohort of 497 girls born in Christchurch, published in 2011, found the average age of menarche was 12.1 years old, as well as an association between earlier menarche and increased risks of STDs and teenage pregnancy,” she said.
“By comparison, the NZ Health Survey of 2014/2015 found the average age of menarche to be 13.2 years.”