BOSTON, MASSACHUSETTS. Some people love to watch television late into the night while others retire before the 10 o'clock news. Is this just habitual behaviour or do some people actually need more sleep than others? Researchers at the National Institutes of Mental Health have just completed an experiment to shed some light on this question. The study involved 10 healthy volunteers (5 women and 5 men aged between 20 and 30 years) who habitually got more than 9 hours of sleep every night ("long sleepers") and 14 volunteers (8 women and 6 men aged 21 to 34 years) who slept less than 6 hours a night ("short sleepers"). The long sleepers usually went to bed around 11 pm and woke up around 9 am while the short sleepers went to bed at around 1 am and awoke around 6:30 am. The researchers found that the long sleepers experienced a significantly longer period of high melatonin levels and a longer period of low body temperature than did the short sleepers. The interval of increasing cortisol levels was also longer for long sleepers and the peak cortisol level was reached later (9 am) than in short sleepers (6:30 am).
The researchers conclude that the body's internal Circadian pacemaker, which governs sleep duration, is
genetically programmed to stabilize an individual's sleep duration to prevent sleep deprivation which may be
implicated in the development of conditions such as diabetes, hypertension, and memory loss. They also
point out that the presence of a genetically programmed pacemaker makes it difficult to willfully change
sleep patterns and may account for the detrimental effects of shift work.