GIRLS as young as five are showing signs of early puberty and doctors warn that obesity is a major factor.
It is a worrying development for Irish parents as at least 370,000 children in Ireland - more than a quarter - are overweight or obese and the number is rising by at least 10,000 a year.
The average age for a girl to start puberty has fallen by five years in the past century, with the average age today being just over 10.
Professor Richard Sharpe, an expert in early puberty at the Medical Research Council, said: "Obesity is the biggest factor that we know of. There's clearly something else. Is it environmental chemicals, is it societal stress? I would say on the evidence, environmental factors are not a major player."
Heavier girls would start puberty earlier, he said. However, a number of social stress factors might be playing a part.
He said that more research is needed, but for now, parents need to look at their child's weight.
"People want to look to something outside to blame. But obesity is the biggest player we know of, " he said.
According to the HSE, an unusually early puberty would be diagnosed if symptoms of puberty "start before six to eight years of age in girls and nine years in boys".
It said that "for most girls, there is no known reason for starting puberty early. In boys, early puberty is less common and more likely to be associated with an underlying medical problem".
GPs may recommend a blood test to check for any problems with hormones to diagnose the cause of early puberty. Scans may also be used to check for tumours and the function of glands and organs.
The HSE website said that treatment with medication is usually only recommended "if it is thought that going through an early puberty would cause you problems later in life, such as having weak bones or growing up particularly short. If this is not the case, having an early puberty will not usually cause an health problems."