A new study suggests that girls are starting to hit puberty nearly a year earlier than they did 4 decades ago.

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

Researchers from the University of Copenhagen in Denmark assessed data from 38 studies, which involved tens of thousands of girls all over the world.

Each study examined when the development of the glandular breast tissue, which is also known as thelarche, began to take place.

The thelarche is a key marker of the onset of puberty.

This was found to have crept forwards by 3 months per decade between 1988 and 2013.

Puberty among girls generally starts from the ages 8 and 13, but in Europe, recent studies found that the average onset among girls is now about 10 years.

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.”

The pointed to US Researcher that was 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 than those girls that are in the normal weight.

This is because having excess weight causes insulin resistance, which in turn increases the levels of the sex hormone estrogen, which is key in puberty.

Obesity rates are rapidly increasing all over the world as junk food becomes more readily available for kids.

It is said that 2 billion people all over the world are overweight or obese.

70 percent of the overweight or obese people come from low or middle-income countries.

In Britain, a third of children and 2 thirds of adults are overweight.

The Danish researchers pointed out that obesity is not the only theory that is driving early puberty in girls.

Chemicals in the environment such as endocrine are another possible cause.

Many of these, such as insecticides DDT and DDE have been banned, but they still remain as pollutants in the soil.

The researchers wrote, “Changes in age at pubertal onset may serve as a sensitive indicator of environmental influences on human health. The banned but persistent chemicals such as DDT (dichloro-diphenyl-trichloroethane) and DDE (dichloro-diphenyldichloro-ethylene) have been associated with earlier age of puberty.”

The researchers said psychological factors can also have an influence on the age of puberty.

Stress is known to fasten the biological transition to adulthood.

Early puberty is also linked to higher lifetime risk of health conditions such as heart attack, stroke, and cancer.

Early puberty is also linked to early menopause.