[The importance of sleep in the mental health].

Japanese average sleeping time is decreasing year by year. The National Sleep Foundation of United States of America released that Japan reports the least amount of sleep. Japanese reports sleeping about 30 to 40 minutes less on workdays than those in the other countries surveyed, averaging 6 hours 22 minutes of sleep. There are many reports that insomnia has been suggested to cause depression and other mental disorders. And epidemiological evidence supports a link between sleep loss and obesity. Obesity is one of risk factors of obstructive sleep apnea syndrome which causes cognitive dysfunction, mood disorders and so on. Sleep loss and sleep insufficiency can cause mental disorders and be impaired cognitive function and performance.