Sydney - Some are calling sleep the new sex - lives are so frazzled that at the end of the day what many adult Australians long for isn't a cuddle but temporary death.

When the working day begins and ends in the dark, the absolute height of luxury has become slipping between the sheets for five, six, even seven hours.

Doctors worry that the sleep-deprived are getting ever younger.

The chronic tiredness that comes with a frantic lifestyle, according to University of South Australia researcher Tim Olds, is causing "serious drop-offs in school performance, attention and memory."

In the first, large-scale local study of children's sleeping habits, Olds found that teenagers were missing out on an average of one hour's sleep during the school week. Half of children weren't getting enough sleep during the week and a quarter were in deficit at the weekends too.

Surprisingly, perhaps, television is not the culprit. Bedtime is put back by socializing, listening to music and family matters.

"Kids' time is much more regimented than it was previously and (late evenings) may be the only time they get to chill out," he said.

Lifestyles have changed but the need for sleep has not. The recommendation is that those aged 13-18 need at least eight and a half hours' sleep a night. Younger children are best with nine to 
11 hours.

In the past, it was easier to get children to bed. The television close-down came earlier, bedrooms were not lit with the twinkling lights of video games, computers and hi-fi systems. Even the street outside was quieter. Parents went to be earlier too.

Academic performance is not the only casualty. Children get grumpy and may develop psychological problems. There is also the link between lack of sleep and extra kilogrammes.

Olds found that overweight children were spending less time in bed than those of normal weight. The big debate about this is whether obesity causes lack of sleep or whether it's the other way round and sleep deprivation is causing children to put on weight.

Olds, who reckons the latter may be true, said: "It seems very likely that it's the low sleep duration that's contributing to obesity, probably through various hormonal mechanisms that we know are associated with sleep deprivation." (dpa)