My impression, during the past several years, is that many people are sleeping less than would be considered adequate for optimal overall well being and functioning. However, the definitions of "too little" vary somewhat and the available research on the subject provides rather mixed information.
The National Sleep Foundation in the United States maintains that eight to nine hours of sleep for adult humans is optimal and that sufficient sleep improves alertness, memory, problem solving ability, and overall health, as well as reducing the risk of accidents. A widely publicized 2003 study performed at the University of Pennsylvania School of Medicine demonstrated that cognitive performance declines with fewer than eight hours of sleep. However, a University of California, San Diego psychiatry study of more than one million adults found that people who live the longest self-report sleeping for six to seven hours each night. It is also true that like so many things, one formula does not necessarily apply to everyone. There are those who thrive well with much less sleep than others who begin to malfunction if they don’t satisfy their minimum sleep requirement.