Many Australian kids stay up late on Sunday nights, affecting them with sleep deficit that compromises their performance at school throughout the week.

According to the study of sleep patterns of more than 4,000 children across Australia, Professor Tim Olds said poor sleep was a known to trigger memory recall problems and cognitive impairment.

Overall, based on his study, many children were sleep deprived for up to two to three hours from Monday through Friday, he said and this affected not only their education.

Kids who are overweight and obese sleep less, said Prof Olds from the University of South Australia.

And it's probably because they sleep less they have a predisposition to being overweight, and not the other way around.

Prof Olds said weight gain could be the result of these children being less active in general, as they often also had more screen time spent watching TV, using a computer or games console.

He also said that poor sleep routine could also cause hormonal changes that would promote weight gain.

It may be hormonal disruption, said Prof Olds.

We know that short sleep can increase the hormones which make you very hungry and decrease the hormones which make you feel satisfied.

The study which involves children aged 9 to 17 is published in the Australian and New Zealand Journal of Public Health.

Prof Olds referred to another study from Korea - a country which he said had an extreme study culture - warned Australian adolescents were moving in that direction in terms of sleep.

Korean 18 year olds sleep 4.5 hours on school nights and 13.5 hours a night over the weekend.

On Sunday, (Australian children) are in the habit of staying up late to midnight and beyond and they still have to get up to go to school.

They accumulate this sleep deficit on Sundays that increases on Monday to Thursday, and they have a big catch-up on Friday and Saturday before the whole cycle begins again.

Australian parents are advised to focus not on trying to get their children to sleep more; rather they should seek to make a child's sleep more consistent through the week.

The important thing is to even out the sleep they get, concluded Prof Olds.

Australia