LONDON: Growing levels of obesity are seeing some girls start puberty as young as seven, studies show.
Experts say the extra fat tissue is encouraging young bodies to produce hormones which kickstart sexual changes.
Researchers in the U.S. found that one in ten girls aged seven had developed breast tissue, one of the first signs of puberty.
Doctors in Britain backed up the research, saying they have treated girls of seven and eight with puberty problems.
They warn that the early exposure to oestrogen has serious health implications because it puts the girls more at risk of breast cancer and heart disease.
They are also more likely to be bullied and could be encouraged into sexual relationships by teenage boys who take them to be a few years older.
Dr Jeremy Allegrove, a consultant paediatrician at the Royal London Hospital, said: ‘We do see girls as young as seven and eight who have started puberty.
'The reason we see them is that mothers bring them in concerned that they are developing very early and will be starting their periods before secondary school. ‘It is only a small amount. I could not say how many.
‘Sometimes we treat them to delay the onset of puberty, sometimes we don’t, depending on the circumstances.’
The U.S. study, published in the journal Pediatrics, is further evidence of a trend which has seen the age of puberty plunge dramatically over the past 200 years. By the 1950s it had fallen from around the age of 15 to 11 or 12.
The researchers from the Cincinnati College of Medicine and Mount Sinai School of Medicine in New York and Kaiser Permanente in San Francisco studied more than 1,239 young girls.
They found that almost one fifth of white girls aged eight had reached puberty compared with a third of Hispanics and almost half of black girls.
Frank Biro, director of adolescent medicine at the Cincinnati Children’s Hospital Medical Centre, who led the research, said teenage boys may be sexually attracted to very young girls, who appear older than their actual age, potentially putting pressure on them.
‘We need to understand better all the factors that are contributing to earlier maturation,’ he added.
There are no figures available for the numbers of seven and eight-year-old girls starting puberty in Britain.
However, it is likely that the figure would not be as high as it is in the U.S. because obesity rates are lower here.
Earlier this year a Danish study revealed that girls were starting puberty roughly a year earlier than they would have done two decades ago.
The researchers, from the University Hospital in Copenhagen, warned that earlier development could lead to increased sexual activity among youngsters.
Girls who start puberty early often say they are teased at school, particularly when getting changed for PE when their classmates can see they are wearing a bra.
Al though researcher s say obesity is the main cause of earlier puberty, other factors may be responsible.
Some scientists believe the trend is linked to a chemical called bisphenol A, a plastic found in the lining of tin cans and babies’ feeding bottles.
Men with high levels of bisphenol A in their bodies are more likely to have low sperm counts, according to one study.