Girls who menstruate at an early age likely to have sons, research

The age when a girl goes through puberty has long been linked to when her mother started menstruating, and a new study adds to evidence suggesting the same holds true for boys.

Researchers surveyed almost 16,000 youth in Denmark about their progression through puberty every six months starting when participants were 11 years old and continuing until they fully matured or reached 18. Researchers also surveyed mothers during pregnancy about their age when they first began menstruation.

Compared to mothers who were late bloomers, those who started menstruating at a younger age were more likely to have sons with earlier genital and pubic hair development as well as earlier voice changes, facial hair growth, acne and first ejaculation, the study found.

Daughters of women who developed early were more likely to start menstruating and developing breasts at a younger age and they, too, were more prone to early acne and pubic hair growth.

“A mother that had early puberty is more likely to turn ‘genes for early puberty’ over to her children,” said study co-author Dr. Nis Brix of Aarhus University in Denmark.

“Because these ‘genes for early puberty’ affect both boys and girls, both sons and daughters will on average be expected to go through puberty earlier,” Brix said by email. “That’s the most likely explanation.”

Children who go through early puberty may be shorter than average adults because after their early growth spurt, their bones may stop growing at a younger age, and they are also at increased risk of obesity as adults. During adolescence, they may face an increased risk of social and emotional problems and earlier sexual experiences.

A younger age at puberty has been linked to increased risk of diseases in later adult life, such as breast and testicular cancer, diabetes and cardiovascular disease.

Some recent research points to puberty onset becoming earlier in general, especially for girls in developed countries. Environmental factors like diet, obesity and chemicals that mimic human hormones have all been suspected of playing a role.

The current study does offer some evidence to suggest genetics are not the only factor influencing puberty timing for girls, and environment is also playing a role.

That’s because the timing of girls’ menstruation and breast development was more strongly associated with mothers’ own development timeline than other aspects of female maturation like pubic hair or acne, researchers note.

Based on the mothers’ responses about when they started menstruating, the researchers found that half of the women were 13 years, 3 months or older. So, the study team categorized maternal menstruation starting at age 12 or younger as “early” and starting at age 15 years or older, as “late.”

They found that breast development, for example, started up to six months earlier in girls whose mothers had experienced early menstruation than for their peers, or up to four months later than peers in girls whose mothers had started puberty later.

Similarly, voice breaking happened a little over two months earlier than peers in boys whose mothers had an early puberty, and underarm hair developed three months earlier.

The study wasn’t designed to prove whether or how mothers’ puberty timing influenced development in their children. Another limitation is that it relied on surveys rather than medical records or exams to determine the participants’ timeline for development.

Still, the study adds to growing evidence suggesting that mothers’ puberty timing and genes may impact the timeline of maturation for both sons and daughters, said Qiguo Lian, a researcher at the Shanghai Institute of Planned Parenthood Research and Fudan University in China who wasn’t involved in the study.

“Many factors can influence timing of puberty,” Lian said by email. “A child may start puberty earlier because she/he is obese or just her/his mother (started menstruation) earlier.”

Early puberty might not necessarily lead to physical or mental health problems, but parents should be aware of this possibility, said Jane Mendle, a human development researcher at Cornell University in Ithaca, New York, who wasn’t involved in the study.

“Certainly, not every child who goes through puberty early will have a rough time later in life,” Mendle said by email. “But it’s important to recognize that this transition can be a pivotal one in people’s lives.”

SOURCE: bit.ly/2qYBaob Human Reproduction, online October 12, 2018.