"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 WVU'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.
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 WVU study were unable to determine the causal relationship between how long a person sleeps and cardiovascular disease.
But they pointed out that sleep duration affects endocrine and metabolic functions, and sleep deprivation can lead to impaired glucose tolerance, reduced insulin sensitivity and elevated blood pressure, all of which increase the risk of hardening the arteries.