Too little sleep linked to heart disease risk.

People who do not sleep a lot are more likely to suffer from negative health effects than people who sleep more than eight hours a night.

People who tend to get less than six hours sleep a night are more likely to have high blood pressure, high cholesterol, diabetes and tend to be obese, a large US study has found.

The research is the first to look at differences in risk between racial and ethnic groups and also finds the strongest effect among black and Hispanic Americans.

"This is important, since racial minorities are generally at increased risk of cardiovascular disease, diabetes and obesity," said Michael A. Grandner, who led the study at the Centre for Sleep and Circadian Neurobiology at the University of Pennsylvania in Philadelphia.

"And if they also tend to have more sleep difficulties, that could be making things worse," said Grandner.

Poor health

Using nationwide survey data from 2008, researchers divided results from more than 5 000 respondents representing the US population into three groups: people who were sleeping less than five hours a night; the next group who slept between five and six hours and people who slept more than nine hours a night.

Grandner's team reported in the journal Sleep Medicine that people who didn’t sleep a lot and the next group were both linked to poor health. 

People who didn’t get a lot of sleep were twice as likely to have high blood pressure and high cholesterol, compared to people who slept around seven to eight hours a night. People who slept the less were also 75% more likely to have diabetes and 50% more likely to be obese. They were 20% more likely than normal sleepers to report high blood pressure and obesity. 

Blacks were most likely to report sleeping less than five hours and the same group was also most strongly linked to obesity.

Populations
Sleeping just a few hours at night was strongly linked to high blood pressure among blacks, whites and non-Mexican Hispanics, while people of Asian descent had the strongest link between short sleep and high cholesterol.

People who slept the longest at night did not appear to experience any negative health effects once researchers adjusted for other factors. 

There is no consensus on what the ideal minimum amount of sleep should be for good health, Kristen L. Knutson said.

She studies sleep and heart health in different populations at the University of Chicago’s  Department of Medicine.

Younger people

There’s no set number for sleep, in part "because there is likely to be some variability in how much sleep different people need," Knutson said, but the majority of large studies had found that people who said they slept between seven and eight hours a night were the healthiest.

"Recommendations vary by age, with younger people generally needing more sleep than older people.

"Like most aspects of health, too little is bad for you and too much is also likely bad for you," Grandner said.

"It’s hard to say that short sleep is worse than sleeping too many hours - it's just that we currently have a better idea of why short sleep is detrimental to health," she said.

Quantity of sleep isn't the only important factor though, Grandner said.

Insomnia, sleep apnoea and waking frequently during the night may be related to heart disease, diabetes and obesity.

Stress on  the body

"These data do suggest that short sleep, whatever the cause, is associated with important negative health outcomes," Knutson said.

Sleep and health are likely linked in a two-way relationship, Grandner said. 

Less sleep may negatively impact health and certain health conditions like obesity might make sleep more difficult.

"Lack of sleep limits your body's ability to keep itself healthy, increasing risk for disease, which puts stress on the body, making sleep harder," he said. 

"It is likely a cycle like this."