Girls start puberty a year earlier than they did in 1970s

GIRLS are starting puberty nearly a year earlier than they did four decades ago, research suggests.

Scientists believe the global obesity epidemic may be to blame for this because being overweight skews the hormones in the body.

The researchers, from the University of Copenhagen in Denmark, assessed data from 38 studies involving tens of thousands of girls from around the world.

Each study examined when the development of glandular breast tissue – which is known in medical terms as ‘thelarche’ and is a key marker of the onset of puberty – began to take place.

This was found to have crept forwards by three months per decade between 1977 and 2013.

Puberty among girls generally starts between the ages of eight and 13. But in Europe, the most recent studies found that the average age of onset among girls is now about ten years.

Boys tend to start puberty slightly later than girls – about a year on average.

The researchers told JAMA Pediatrics medical journal: ‘The ongoing global obesity epidemic could partially explain the observed change in age at pubertal onset assessed as age at thelarche.’

They pointed to US research, published in 2017 in the International Journal of Environmental Research and Public Health, which found that obese girls were more than twice as likely to start puberty early than those of normal weight.

This is thought to be because being overweight causes insulin resistance, which in turn increases levels of the sex hormone oestrogen, which is key in puberty. Obesdriving ity rates are soaring across the world as junk food becomes more readily available and income levels increase in developing countries.

Two billion people worldwide are overweight or obese – with 70 per cent of them in low or middleincome countries. In Britain, a third of children and two-thirds of adults are now overweight.

The Danish researchers, however, pointed out that obesity is not the only theory as to what is

early puberty. Chemicals in the environment –including ‘endocrine [gland]-disrupting’ chemicals – are another possible cause. Many of these, such as insecticides DDT and DDE, have been banned but remain as pollutants in the soil.

‘Changes in age at pubertal onset may serve as a sensitive indicator of environmental influences on human health,’ the team of researchers wrote.

‘The banned but persistent chemicals such as DDT (dichlorodiphenyl-trichloroethane) and DDE (dichloro-diphenyldichloro-ethylene) have been associated with earlier age of puberty.’

Psychological factors may also have an influence on the age of puberty, with stress thought to hasten the biological transition to adulthood.

One study found that children who were adopted from a developing country to parents in Denmark were up to 20 times more likely to start puberty at an early age.

Other research has found similar trends among children immigrating to Sweden, France, Belgium, Switzerland and the US.

The early onset of puberty is linked to a higher lifetime risk of heath conditions such cancer, heart attack and stroke. It is also linked to early menopause.

‘Obesity may be to blame’