Danish children are reaching puberty earlier

January 2, 2019 - 06:25

A new study shows that Danish children start puberty earlier than their parents did.

Researchers have collected information about puberty from almost 15,000 Danish children. (Photo: Shutterstock)

Girls today are getting their first menstrual period three months earlier than their mothers did, according to a new study. The first menstrual period – or menarche – is often used as an important marker of when girls start puberty.

The research also shows that Boys reach puberty six months to a year earlier than they did 15 years ago., and that male voices drop a year earlier than previously documented.

The researchers have collected information about puberty from 14,759 Danish children. The children answered a total of 73,160 questions over a 6 month period. The questions dealt with their puberty development from the time they were 11.5 years old.

The girls were asked about how their bodies changed (when they developed breasts, pubic hair, pimples, and underarm hair) and when they had their first period. The boys were asked about when their voices changed, when they had their first ejaculation, and developed pubic hair, pimples, and underarm hair. Researchers used this information to determine when the children reached puberty.

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Results apply to other countries

According to Nis Brix, one of the scientists behind the research, the new results should be viewed alongside previous studies.

"The finding that boys hit puberty six months to a year earlier than previously is particularly uncertain. Earlier Danish studies collected information differently from the way we did in our study, but if you look at this study next to the previous research, they point in the same direction. Both boys and girls are starting puberty earlier," says Brix in a press release.

The researchers will now see if they can explain the trend of earlier puberty by events that occur at the foetal stage. In doing so, they might even be able to halt the trend.

In Norway, the age of girls' first menstrual period has also dropped.

"This trend was first described in Norway decades ago. Earlier onset of puberty has probably been going on for well over a hundred years and seems to be continuing," says Fartein Ask Torvik, a researcher at the Norwegian Institute of Public Health.

He explains that studies from other continents are also showing the same trend.

"For example, the average age of menarche fell from age 17 to 13 in South Korea during the 20th century," says Torvik.

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Researchers know relatively little about puberty in boys

"When it comes to boys, we know very little from earlier research. A lot of studies haven't looked at boys' puberty development as thoroughly as girls'," Torvik says.

He therefore finds it particularly interesting that the Danish study also looked at the earlier age of onset of puberty among boys.

The Norwegian Mother and Child Cohort Study (MoBa) is one of the world's largest health surveys. Among other things, researchers are using the data to further study puberty development in both boys and girls.

Torvik hopes that the MoBa survey will provide more answers and a greater understanding of puberty in boys, since it tracks the progress of children born in the early 2000s.

The researchers are now waiting for all of the survey participants to reach puberty before they start analysing the information.

There could be several reasons why puberty occurs earlier for some individuals than others. Genetics, nutrition, physiology, and higher body fat percentages are important factors.

"Some studies have also shown that different forms of stress may be the cause, but it's difficult to distinguish between associations and causes," says Torvik.

He believes that the decline in age has taken place over such a short time period that it points to changes in the environment, not in the genes.

"The most important single factor is probably a change in nutrition. But we don't fully know why that's the case," said Torvik.

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Could it be a good thing?

Torvik explains that reaching puberty earlier is not necessarily a disadvantage, but it depends on how much earlier we're talking about.

"Some studies using Finnish and British data indicate that early maturation may correlate with doing well at school, especially for boys. However, there is some uncertainty around these results," says Torvik.

Overall, girls reach puberty earlier and tend to do better than boys at school.

"The difference in school performance is greatest exactly when puberty differences are the greatest," Torvik says. He wonders whether early maturation might help explain gender differences in school performance.

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Read more in the Norwegian version of this article at forskning.no

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