The sleep is a state of natural rest and it is necessary for survival. The sleep is a dynamic time of healing and growth processes. According to the National Sleep Foundation an adult person needs eight to nine hours of sleep in order to be alert, able to solve problems and in good overall health. Another study found that people who live the longest sleep for six to seven hours, but this could have something to do with the fact that older people tend to sleep less or perhaps a genetic ability to generate cells faster gives an advantage in some cases.Other researchers concluded that not getting enough sleep doubles the risk of death form cardiovascular disease, but sleeping too long also hides risks. As a conclusion the most sources advise us to sleep around 7 to 8 hours per night in order to be healthy and to reduce the risk of diseases.

Photo: Dan Hershman; source: Flickr.com