• Sun
  • Dec 28, 2014
  • Updated: 6:53pm

The dangers of staying up late

PUBLISHED : Tuesday, 23 March, 1999, 12:00am
UPDATED : Tuesday, 23 March, 1999, 12:00am

Many children in Hong Kong suffer from a deprivation that could seriously impair their mental and physical development. They are not spending enough time in bed.


Although there is no consensus as to how many hours of sleep children need, paediatricians recommend a minimum of 10.25 hours a night for a child aged eight and 10 hours for nine-year-olds, though individual children may have different needs. Many primary school children of this age, though, are sleeping at least two hours less than the minimum.


Of 135 pupils in the Primary Four year at Baptist Lui Ming Choi School in Sha Tin, 34 children said they slept between eight and nine hours, and 14 children said less than eight hours - two less than the suggested minimum. Forty-five children slept between nine and 10 hours and only 42 said they had more than 10 hours' sleep a night.


Victoria English Primary School's Primary Three class conducted a similar survey on sleep as part of its general-studies course. This revealed 11 out of 41 pupils sleep less than eight hours a night and 21 less than nine. None slept for 10 or more hours.


Many children in the class said they did not go to bed before 11pm, or even midnight, so they could finish their homework and watch television dramas. They were all up by 7am to start school an hour later.


Most parents, and even teachers, are unconcerned. Bed by 9.30pm is regarded as early.


But Dr Simon Wong Kam-kee, a paediatrician, warns that many Hong Kong children may be sleep-deprived, with damaging consequences. 'The requirement is way above eight hours. A child of eight requires definitely more than 10 hours. It is wrong for a child to be given sleep of eight to nine hours, or even less,' he says.


'If children don't get enough sleep it affects their growth and development, and even their ability to learn, because their body functions need those hours of sleep to recuperate.


'If a person is deprived of sleep they will become irritable, emotionally unstable and will have difficulty in their learning.' A child's learning capacity could be reduced by even one hour's lack of sleep, he warns.


The results of this informal study are indicative of the lack of awareness about children's sleeping needs. Homework, television and other activities take precedence over giving brains and bodies enough 'down time'.


Dr Wing Yung-kwok, director of the Sleep Assessment Unit at the Chinese University of Hong Kong, says lack of sufficient sleep is a hidden problem in Hong Kong, one that teachers and parents should be more concerned about.


Until now, children's sleeping habits here have not been seriously studied. But Dr Wing's unit has completed a preliminary study involving 280 children aged seven to 16, with a mean age of 11.5.


The time they spent sleeping ranged from five to 12 hours, with the mean being 8.5. Fifteen per cent said they slept less than eight, while 20 per cent complained of fatigue and finding it hard to wake up.


At weekends, they sleep at least an hour longer, which indicates they are sleep-deprived during the week, says Dr Wing.


The 8.5-hour average may be considerably less than children sleep in the United States. A recent study conducted by the Institute for Social Research at the University of Michigan found the average there was 10.75 hours a night. The 22 eight-year-olds in Dr Wing's study did, though, sleep 10 hours on average, though the seven-year-olds slept 9.25, an hour and a quarter less than recommended in Nelson's Text Book of Paediatrics. While it is normal for young Hong Kong children to be up late, it is not in the West.


This difference is reflected in indications that children studying in an English Schools Foundation school sleep more. Jenny Quinton, a teacher at Kennedy School, found only a handful of eight-year-olds slept less than 10 hours a night. The exact functions of sleep are still unknown, and the amount required varies between individuals.


'But we know we definitely need sleep. The longest recorded duration for a person not to sleep is around one week. There is no single person who does not require sleep,' says Dr Wing.


Growth hormones are secreted at night, and children who sleep poorly do not grow as well, says Dr Wing.


Sleep allows the body to rest. There is also a hypothesis that there is a link between creativity and longer periods of rapid eye movement (REM) sleep. REM sleep, when dreams are most likely to occur, happens around every 90 minutes and increases in duration the longer a person stays asleep. The first period lasts for five to 10 minutes but later periods can extend to about an hour.


In Dr Wing's survey, usual bedtime was found to be 10.30pm, as reported by 40 per cent of the children. But one-third said they slept at 11.30pm. One-third woke at about 7.30am and a quarter at 6.30am.


Dr Wing was also surprised that a large number of children experienced sleep problems. Ten per cent said they had difficulty falling asleep or woke too early at least three times a week and five per cent felt anxious while falling asleep. Dr Wing says these were indications of stress. Most children reported experiencing these problems from the age of seven, when pressures of school increase.


The study is highly revealing as to how children spend time before going to bed. Children in the survey spent an average of three hours a day doing homework, four hours watching television and one hour playing computer games. Only 12 children have regular afternoon naps to compensate for being up late at night. In the mainland, this tradition is still prevalent, a natural way of avoiding the hottest hours of the day.


Dr Wing plans to extend his survey, but only a handful of schools were willing to take part in the first study. This indicates a lack of interest in the issue, he says. 'Sleep in children is under-studied, in Hong Kong and internationally.' Dr Wong, the paediatrician, says the pressures of Hong Kong's education system and our urban lifestyle cause many children not to spend enough time in bed. Working parents often return home late and expect to enjoy the company of their children late into the evenings. This may also be the only time they have to help their children with homework.


Many parents and teachers believe that the more work a child is given during school and at home, the more they will excel. The reverse, though, may be true if their learning ability is reduced by lack of sleep.


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