Women who started their periods before their peers go on to have sons who enter puberty early, research suggests.
Mothers who first menstruated between eight and 11 years old later have sons whose armpit hair grows two-and-a-half months before most boys, a study by Aarhus University found.
These boys are also more at risk of developing acne and having their voices break two months earlier than normal, the research adds.
And the daughters of women who started their period young often develop breasts six months earlier than other girls, the study found.
Teenage boys enter puberty earlier if their mothers started their periods at a young age (stock)
The Danish researchers, led by Signe Sørensen, analysed 15,822 11-year-olds from 2012 to 2016.
Of the participants, which were taken from the Danish National Birth Cohort, 8,125 were girls.
Every six months, the participants answered questionnaires about what stage of puberty they were in.
While they were pregnant, the participants’ mothers provided information on when they started their periods.
Results, published in the journal Human Reproduction, suggest when a mother starts her period influences when her son first ejaculates and develops pubic hair.
The timing of their mother’s first bleed is also linked to genital development, armpit hair growth and voice breaking in teenage boys.
IS POVERTY LINKED TO PUBERTY ONSET?
Children from poor families are up to four times more likely to start puberty early, research suggested in June 2017.
Boys are at the greatest risk, yet disadvantaged girls are still twice as likely to prematurely develop breasts or pubic hair, a study found.
Researchers believe this may be due to poverty causing youngsters stress, which leads to the early release of reproductive hormones.
Previous research suggests an early puberty increases a person’s risk of certain cancers, such as breast and endometrial in women, and prostate in men.
The past study’s author says parents can help delay their child’s puberty onset by encouraging them to exercise and eat well.
This is because overweight youngsters have more energy reserves that ‘trick’ the body into sexually maturing.
The researchers, from Murdoch Children’s Research Institute in Australia, asked 3,700 parents of children aged between eight and 11 years old whether signs of puberty had occurred.
Signs in girls include developing breasts, pubic and armpit hair, menstruating and acne. Puberty symptoms in boys include acne, facial and pubic hair, and muscle and height growth.
The researchers then compared the families’ incomes, level of education and occupations.
The study defined nine-to-14 as being a normal age for a boy to start puberty.
In girls, an early period was deemed to be starting at eight-to-11, while a late puberty began at 15-to-19.
A woman’s first period particularly influences when her daughter will menstruate and develop breasts.
It also affects when she grows pubic and armpit hair, and suffers from acne.
‘Whenever a doctor meets a patient with delayed or early onset of puberty, the doctor obtains a family history,’ study author Dr Nis Brix said.
‘The relationship between the mother’s pubertal age and the son’s pubertal age has been taken as common knowledge but now our data from a large study confirms it.’
Starting puberty at a young age has been associated with a greater risk of depression and anxiety.
This thought to be due to teens, particularly girls, feeling sexualised at a young age, as well as being self conscious of their changing bodies.
An early puberty has even been linked to cancer.
This is due to people having higher levels of certain hormones in their bodies for longer over their lifetimes.
Research suggests girls are starting their periods four months earlier every decade.
In the 1800s, both sexes typically started puberty in their late teens, while between eight and 13 is now the norm for girls and nine-to-14 for boys.
Rising rates of obesity may be to blame, with research suggesting a link between a child’s BMI and when they first show symptoms.
Stress and exposure to chemicals, such as pesticides, have also been named as potential culprits.
This comes after research released last year suggested children from poor families are up to four times more likely to start puberty early.
Boys are at the greatest risk, yet disadvantaged girls are still twice as likely to prematurely develop breasts or pubic hair.
Researchers, from Murdoch Childrens Research Institute, Melbourne, believe this may be due to poverty causing youngsters stress, which then leads to the early release of reproductive hormones.