A new study has looked into sleep problems and daytime fatigue in 33 U.S. states and identified the states that are most sleep-deprived.

"People need to understand that sleep is an important part of health. This study tells us that there are certain regions of the country struggling with sleep problems more than others," study researcher Michael Grandner of the University of Pennsylvania told LiveScience.

Dr. Gradner works at the university's Center for Sleep and Circadian Neurobiology. He and his research team studied data from 157,319 participants who had answered two questions. The first was on the number of days over the prior two weeks (from zero to 14) they had trouble falling asleep, staying asleep or sleeping too much.

Second question was on the number of days they felt tired or had little energy within the same period.

Those who answered six out of 14 days to the questions raised were identified as persons with real sleep problems.

According to Dr. Grandner, "three nights per week" is the most commonly accepted cutoff for determining whether insomnia is classified as a separate disorder. This means the cutoff he and his team decided on "has some clinical relevance."

The sleep survey yielded the following rankings:

10 states with the highest sleep disturbance: (percent of individuals who reported six or more days of sleep issues)

West Virginia: 26 percent

Oklahoma: 24.7

Mississippi: 22.4

Alabama: 22.3

Arkansas: 22.1

Missouri: 21.3

Utah: 21

Louisiana: 20.8

Michigan: 20.4

Nevada: 20

10 sleepiest states: (percent of individuals with daytime fatigue for six or more days)

Mississippi: 30 percent

West Virginia: 29.9

Oklahoma: 27.7

Alabama: 27.1

Arkansas: 26.8

Louisiana: 25.4

Missouri: 25.2

Tennessee: 24.4

Utah: 23.8

Delaware: 23.5

The National Sleep Foundation has maintained that there is no definitive number when it comes to the number of hours that a person must sleep because sleep requirement varies per individual.

In its website, the foundation cites a 2005 study, which "confirmed the fact that sleep needs vary across populations, and the study calls for further research to identify traits within genes that may provide a "map" to explain how sleep needs differ among individuals."