Individuals who slept less than 6 hours per day had twice
the risk of myocardial infarction(odds ratio, 2.04) or
stroke(OR, 2.01), compared with those who slept 6-8 hours
a day, even after adjusting for a multiple confounders
associated with cardiovascular risk.
Individuals with less than 6 hours of sleep duration were also
at increased risk of heart failure(OR, 1.67).
Intriguingly, persons who slept more than 8 hours per night
had a twofold increased risk of angina pectoris(OR, 2.07)
as well as an increased rsik of coronary artery disease
(OR, 1.19).
It seems that the optimal time is 6-8 hours.

Dr. Rohit R. Arora, Chair of Cardiology and professor of
medicine, at the Chicago Medical School reported the above
findings at the Annual Meeting of the American College of
Cardiology.

The analysis included 3,019 individuals, at least 45 years
of age, who participated in the 2007-2008 National Health
and Nutrition Examination Survey(NHANES).
Patients were asked about sleep quality and then stratified
into one of three categories:
fewer than 6 hours of sleep a night, 6-8 hours a night, and
more than 8 hours of sleep per night.

The analysis adjusted for the covariates of age, systolic
blood pressure, gender, body mass index, diabetes,
smoking status, total cholesterol, HDL cholesterol,
sleep apnea, and family history of heart attack.