'Alarming' trend of girls getting their periods younger revealed - and the frightening factors behind phenomenon

The age at which girls get their first period has decreased over the last 50 years, research has shown.

Researchers from Harvard found that girls who are now aged 19 to 24 got their first period when they were 11, on average, compared to women now aged 55 to 74, who were an average age of 12 when they got their first period.

Over fifty years, there has also been a rise in the number of girls younger than nine who start menstruating.

The trend could be due to rising childhood obesity, the researchers said. Previous research has linked the phenomenon to junk food consumption, chemical contamination and certain pollutants.

Menarche, which is the first time girls get their period, usually occurs between age 11 and 15, according to the Cleveland Clinic

Researchers from Harvard found that girls who are now aged 19 to 24 got their first period when they age 11.9 years, on average, compared to women now aged 55 to 74, who were an average age of 12.5 years when they got their first period

The researchers studied 71,341 individuals as part of the Apple Women's Health Study, which used cycle tracking data from iPhones and Apple Watches in addition to surveys to gain extra information about menstrual cycles.

They also found that Asian and non-Hispanic Black participants were more likely to report earlier menstruation.

Other studies have suggested this is unlikely to be due to genetic variations, and may be driven by 'other environmental or contextual factors that may, through racism, impact different pathways, leading to earlier menarche,' the researchers said.

Menarche, which is the medical name for girls' first periods, traditionally occurs between age 11 and 15, according to the Cleveland Clinic.

Girls in the study also reported their period cycle took longer to became regular. 

The amount of participants whose cycle became regular within two years of starting their periods dropped over the past five decades.

The percentage of participants who got their period younger than age 11 increased over the years

The amount of participants who reported regularity within two years of starting their periods dropped over the past five decades

Zifan Wang, the study's lead author, told The Washington Post it was worrying that girls appeared to be taking longer to reach a regular menstrual cycles.

'This is also very concerning because irregular cycles are an important indicator of later-in-life adverse health events. It alarms us. 

'We need to do more early counseling and intervention on irregular cycles among children and adolescents,' Dr Wang said.

Irregular periods has been linked to various diseases including coronary heart disease, type 2 diabetes, and rheumatoid arthritis.

The data also showed that the proportion of girls with very early periods - before the age of nine - was higher in the latest birth group compared with the earliest group. 

The decrease in age at first period could be due to rising childhood obesity, the researchers said, as it is a risk factor for earlier puberty.

Overweight children have higher sex hormone levels and levels of leptin, a hormone produced by fat cells, which can accelerate puberty.

While childhood obesity may play a role, the decrease in age of first period started prior to the obesity epidemic, suggested other factors may be involved.

One big concern is forever chemicals - a group of around 15,000 human-made chemicals which are found in everything from consumer products to food and water.

These can disrupt hormones, potentially bringing puberty on earlier.

Things like poor diet, including lots of sugary foods, stress and adverse childhood experience can also impact the starting point of puberty.

Other research has shown that very early puberty increased during the pandemic, which may have been due to the stress it caused in young children's lives.

The study was published in the journal JAMA Network.