Newborn infants require about 16 hours of sleep per day and as new parents know, they spread this over a 24 hour period. Over time, sleep consolidates and the need for sleep decreases to between 12-14 hours in the second year of life, 10–12 hours by age 3, and to about 10 hours from ages 8-12. Teenagers require between 9-10 hours and mature adults, in general, between 7-9 hours, and contrary to some beliefs the need for 7-9 hours of sleep continues well into old age.
About 3% of the population is thought to have a short-sleep gene and about 3% have a long-sleep gene.
There are however some people who genetically require more or less sleep. About 3% of the population is thought to have a short-sleep gene and about 3% have a long-sleep gene. Those who carry the short-sleep gene sleep on average about two hours less a night — but still function perfectly well. On the other hand those who carry the long-sleep gene need more sleep and it is not unusual for them to require up to two hours more sleep than most other people.
As the short and long sleep gene are a genetic characteristic the need for sleep tends to run in families so if your parents or grandparents typically slept short (or long) hours you are more likely to be like them. However, the vast majority of us do require between 7 - 9 hours for optimal physical and mental health.