In Depth

Why are girls starting puberty earlier?

New study suggests obesity could be linked to breast tissue development

A global study has found that by 2013 girls were starting puberty almost a year earlier on average than they did in 1977.

Co-author Dr Alexander Busch, who is based in Denmark, believes it is the first study to draw together global data on the development of glandular breast tissue, known as thelarche, says The Guardian.

Thelarche is thought to be the best marker of the start of puberty in girls, says the newspaper. As Busch says: “That means also that there are not many studies out there concerning the implications of early breast development for [girls’] lifelong health.”

The study, published in the journal JAMA Pediatrics, could be significant because girls starting their periods earlier are thought to be at higher risk of health problems including obesity and cardiovascular disease.

Bringing together information from 38 separate studies, all published before mid-2019, the team found that the onset of thelarche varied around the world – as well as changed through time.

Ignoring studies that looked at malnourished or pathologically obese children, the new study found that the average age at which girls developed breast tissue in Europe was between 9.8 and 10.9 years. In Africa it was 10.1 to 13.2 years and in the US 8.8 to 10.3 years.

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Why is this happening?

The team was not looking for a cause, just examining the effect – but it does suggest a possible explanation: increased obesity. The researchers point out that a higher BMI (body mass index) is linked to earlier development of glandular breast tissue.

The team cites the “ongoing global obesity epidemic”, saying it could “partially explain” the results. However, one of the limitations of the study is that not all of the data provided included the body mass index of the participants.

It has been suggested several times in the past that increased exposure to chemicals through cosmetics and other sources could be lowering the age at which puberty starts. In 2018, the Daily Mail reported a Californian study suggesting there was a link.

The University of California team said its study suggested exposure to diethyl phthalate, used in perfumes, or methyl paraben, found in hand creams, could make girls start their periods earlier in life.

Another area of uncertainty is whether puberty is both starting and finishing earlier in girls, or is starting earlier and therefore lasting longer.

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