An American study linked life spans with sleep amount and found that those who sleep 4 to 7 hours live the longest, with those sleeping less than 4 or more than 9 hours living shorter lives. The National Sleep Foundation however maintains that 8 hours of sleep is optimal, claiming improved performance in tests, reduced risk of accidents and a better immune system. It is important to mention this does not apply to children and adolescents, particularly children who require as much as 13 hours a night.

Children. Surprisingly enough older children and even teenagers should also be getting a similar amount of sleep and ten hours sleep a day for children is a good figure to aim for.
Teenagers. Teenagers need about 9 hours of sleep a night. For many years it has been thought that teenagers, who were sleeping for more than eight hours a day were simply lazy, but this is in fact far from the truth. Bearing in mind the level of activity that most children are involved in each day, both at school and in their free time, and the fact that their bodies are growing and changing rapidly, there is a genuine need for more than the traditional eight hours of sleep to be given the best conditions for development.

Missing the odd few hours of sleep here and there will not do you any harm but if you find that you're regularly falling short on sleep then this can have serious consequences. We all suffer from the occasional insomnia, but insomnia that continues for more than a month or six weeks can have a marked effect on your health and general quality of life.