Americans suffer from a chronic lack of sleep, according to a study released, which says the problem is a bigger public health problem than is generally recognized.
The report by the Centers for Disease Control and Prevention (CDC) analyzed American sleep patterns, which was gathered by state health departments in phone interviews with more than 400,000 adults around the United States last year.
The study, published in the most recent issue of the Morbidity and Mortality Weekly Report, a health journal, found that almost one-third of Americans get less than seven hours of sleep per night, which is generally considered the minimum for an average adult to feel rested.
As many as 70 million can be classified as having chronic sleep and wakefulness disorders, the CDC study found.
The survey, conducted in 2008, asked the question: "During the past 30 days, for how many days have you felt you did you not get enough rest or sleep?"
Just three Americans in 10, the CDC said, reported no days of insufficient sleep, while one American in 10 reported not having had a restful night's sleep in 30 days or longer, the study found.
Meanwhile, the researched detected notable demographic variations in the amount of shut-eye Americans get, broken down by geographic location, age, race, gender, class and education.
The greatest rates of sleeplessness were found in the southeastern United States and among racial and ethnic minorities, the study found.
People who don't have a high school diploma tend to sleep better than university graduates, for example.
Thirty-eight percent of people with little schooling -- less than a high school diploma or equivalency test -- said they got enough sleep every night during the previous month, while only 28 percent of college graduates said the same.
Women slept worse than men, younger people worse than the elderly, whites slept better than Latinos and blacks, the study showed.
The CDC warned that chronic lack of sleep could have serious health consequences, including depression, obesity and high cholesterol, and is associated with risk behaviors including cigarette smoking and heavy drinking.