How much sleep is really enough? The sleep deprivation studies suggest a minimum of perhaps two hours a day. Psychological studies show that it depends on whether we are larks or owls, or a bit of both. Statistically, it is reported that most healthy adults sleep 15 hours a day.
It is now known that how much we sleep each night may be determined by our genes. Studies of identical twins, who share the same genes, reveal that their sleep is similar in quality and quantity even if they live in different environments for years. We can be trained to sleep a shorter number of hours each night, but it appears that we revert to our former number of hours of sleep when the training is over.
It has also been shown that longer sleepers who sleep more than ten hours each night may not be the healthiest group of people. The American Cancer Society carried out a six year survey which showed that the death rate of these long sleepers was nearly double that of those who sleep between seven and eight hours each night The reverse is also true for short sleepers who claim they sleep less than four hours each night; their death rate is two-and-a-half-times that of average sleepers. At present the exact relationship between sleep and health remains a mystery.
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