By Kevin Buckley in Milan
Watching too much television may distort the hormonal balance of
adolescents and push many of them into early puberty, say researchers.
Many children watch hours of televsion a day
Italian researchers found children denied access to television for just one week experienced a 30% jump in their melatonin levels.
The hormone is thought to prevent the early onset of puberty.
If confirmed, this would be the first sign of a direct physiological impact on television watching upon the young.
Many researchers believe that exposure to on-screen violence and sex has a damaging psychological effect on children - although this theory is hotly disputed.
Researcher Professor Roberto Salti, of the Mayer Hospital at the University of Florence, said: "This is statistically a very significant result.
"It suggests that an excess of television (viewing) can modify some hormones."
Some animals use melatonin to time their reproduction, changing it to suit their environments.
In humans, the hormone regulates the body's internal 'clock'. Levels are at their lowest in the daylight hours, but peak in the evening around eight o'clock as the body prepares for a night's sleep.
Melatonin is also used as a means of regulating sleep patterns for travellers suffering from jet lag.
Professor Salti said: "The hypothesis that TV has a psychological effect on children is widely accepted, but it is very difficult to prove.
"Our hypothesis is that the light and radiation coming from exposure to television screens, and computer screens, disturbs the production of the hormone melatonin, and may be one of the factors influencing the start of puberty.
"There is a big difference between the children of today and those of thirty years ago.
"Today they spend very many hours, five or six a day in some cases, in front of the TV."
The phenomenon of precocious puberty - when children develop the first signs of puberty earlier than the normal ages of ten for girls and eleven-and-a-half for boys - is increasing all over the western world.
In 1990 the first signs of precocious puberty were around the age of eight for girls - the whole process taking two years to complete.
Now, according to Professor Salti, some children enter puberty as young as seven.
Boys, too, are entering puberty at an earlier stage, albeit still slightly later than girls.
Professor Salti believes that there are probably multiple causes for this effect - but he believes that television viewing may be one of those factors.
His work focused on around 75 junior-school children in the Tuscan village of Cavriglia, whose parents agreed to deny them access to television, computers and videogames for a week.
Ball games, public book-reading and other activities were organised by the local authority to involve parents and children.
Although almost 20% of Italian parents say they bar their children from watching television without them, some 14% admit that they permit their offspring to watch
Professor Roberta Giommi, of the International Institute of Sexology in Florence, said: "This is a very interesting development because television is a continuous stimulant, a hyper-stimulant sensorily for the brain, which could well effect children.
"I would be very interested to follow further research."