Magic number for sleep is 7 hours, study finds - INQUIRER.net, Philippine News for Filipinos

Magic number for sleep is 7 hours, study finds - INQUIRER.net, Philippine News for Filipinos

Magic number for sleep is 7 hours, study finds



Philippine Daily Inquirer
First Posted 05:19:00 08/03/2010

Filed Under: Diseases, Health


WASHINGTON—People who sleep more or fewer than seven hours a day, including naps, are increasing their risk for cardiovascular disease, the leading cause of death in the United States, according to a study published on Sunday.

The study, which was published in the journal “Sleep,” found that sleeping fewer than five hours a day, including naps, more than doubled the risk of being diagnosed with angina, coronary heart disease, heart attack or stroke.

The same study conducted by researchers at West Virginia University’s Department of Community of Medicine showed sleeping more than seven hours also increased the risk of cardiovascular disease.

Study participants who said they slept nine hours or longer a day were one-and-a-half times more likely than seven-hour sleepers to develop cardiovascular disease, the study found.

5-hour sleep

Most at risk were adults under 60 years of age who slept five hours or shorter a night. This group increased their risk of developing cardiovascular disease more than threefold compared to people who slept seven hours.

Women who skimped on sleep, getting five hours or fewer a day, including naps, were more than two-and-a-half times as likely to develop cardiovascular disease.

Short sleep was associated with angina, while both sleeping too little and sleeping too much were associated with heart attack and stroke, the study found.

Long lie-in

A separate study, also published in “Sleep,” showed that an occasional long lie-in could be beneficial for those who couldn’t avoid getting too little sleep.

In that study, David Dinges, who heads the sleep and chronobiology unit at the University of Pennsylvania School of Medicine, found that 142 adults whose sleep was severely restricted for five days—as it is for many people during the work week—had slower reaction times and more trouble focusing.

But after a night of recovery sleep, the alertness of sleep-deprived study participants improved significantly.

Greatest improvements

The greatest improvements were seen in those who were allowed to spend 10 hours in bed after a week with just a four-hour sleep a night.

“An additional hour or two of sleep in the morning after a period of chronic partial sleep loss has genuine benefits for continued recovery of behavioral alertness,” Dinges said.

In the study about sleep and cardiovascular disease, researchers led by Anoop Shankar, associate professor at West Virginia University’s Department of Community Medicine, analyzed data gathered in a national US study in 2005 on more than 30,000 adults.

The results were adjusted for age, sex, race, whether the person smoked or drank, whether they were fat or slim, and whether they were active or a couch potato.

Strong association

And even when study participants with diabetes, high blood pressure or depression were excluded from the analysis, the strong association between too much or too little sleep and cardiovascular disease remained.

The authors of the West Virginia University study were unable to determine the causal relationship between how long a person slept and cardiovascular disease.

But they pointed out that sleep duration affected endocrine and metabolic functions, and sleep deprivation may lead to impaired glucose tolerance, reduced insulin sensitivity and elevated blood pressure, all of which increase the risk of hardening the arteries.

Agence France-Presse