In a large U.S. study, people who tended to get less than six hours of sleep nightly were more likely to have high blood pressure, high cholesterol, diabetes and to be obese.
Grandner led the study at the Center for Sleep and Circadian Neurobiology at the University of Pennsylvania in Philadelphia.
Using nationwide survey data from 2008, researchers divided results from more than 5,000 respondents representing the U.S. population into three groups. Very short sleepers got less than five hours per night, short sleepers got between five and six hours and long sleepers got more than nine hours.
Very short and short sleep were both linked to poor health, Grandner's team reports in the journal Sleep Medicine.
Very short sleepers were twice as likely to have high blood pressure and high cholesterol, compared to people who slept around seven to eight hours. Very short sleepers were also 75 percent more likely to have diabetes and 50 percent more likely to be obese.
Short sleepers were about 20 percent more likely than normal sleepers to report high blood pressure and obesity.
Blacks were most likely to report sleeping less than five hours and very short sleep was most strongly linked to obesity among Blacks.
Short sleep 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.
Long sleepers 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.
Knutson studies sleep and heart health in different populations at the University of Chicago Department of Medicine. She was not involved in the new study.
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. "Still, the majority of large studies have found that people who say they sleep between seven and eight hours are 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 is hard to say that short sleep is worse than long - it's just that we currently have a better idea of why short sleep is detrimental to health," he said.
Quantity of sleep isn't the only important factor though, Grandner said. Insomnia, sleep apnea and waking frequently during the night may be related to heart disease, diabetes and obesity, he said.
"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."