UK Edition
The number of girls getting their first period before the age of 11 has doubled amid a rise in childhood obesity, a Harvard study has found.
Early periods can be an indicator of potential adverse health conditions in later life such as an increased risk of cardiovascular diseases, cancers and premature death.
A study of more than 71,000 US women born between 1950 and 2005 were asked when they had their first period, known as the menarche.
The average age was 12.5 years in the 1950s and 1960s, and is 11 years and nine months for those born in the 21st century, data show.
However, the gradual decrease in overall average age is also marked by an almost doubling in the proportion of girls having early or very early periods, classed as before 11 and before nine years respectively.
Around one in seven girls born after 2000 (15.5 per cent) have a period before 11 years old, compared with just 8.6 per cent for the boomer babies.
Those experiencing very early periods before nine years old has also increased from 0.6 per cent to 1.4 per cent.
The scientists said their study could have some errors from women misremembering their first period but that the size of the study population strengthens the data.
A second analysis of 10,000 women who provided data on childhood weight and height as well as their periods found a link between BMI and menarche.
“Exploratory mediation analysis estimated that 46 per cent of the temporal trend in age at menarche was explained by BMI,” the scientists write in the paper, published in JAMA Network Open.
“This finding suggests that childhood obesity, a risk factor for earlier puberty, which has increased in the US, could be a contributing factor to the trend toward earlier menarche. However, the remaining 54 per cent remain unclear.”
The authors also said it was unlikely that genes were to blame for the trend of early periods.
Dr Lauren Houghton, an epidemiologist at Columbia who was not involved in the work, said it was possible that stress also caused earlier periods, a factor overlooked during the Covid pandemic.
“It is very likely that BMI and stress interact to accelerate age at menarche and prolong cycle regularity,” she writes in an editorial published in JAMA.
“My working hypothesis is that more stress increases the pool of androgens and more adipose tissue converts the abundance of androgens into estrogens, leading to earlier puberty.”
Dr Michelle Wise, an obstetrics and gynaecology researcher at the University of Auckland, said: “In my practice, 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.
“Having irregular cycles is associated with long-term health conditions such as mental health, cardiovascular disease and breast cancer.
“In the gynaecologist’s office, 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.
“The epidemic of obesity is contributing to this and not enough is being done at the societal and policy level to address it,” she added.