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CHICAGO -- Skimping on sleep -- or hitting the snooze bar too many times -- may have a negative effect on cardiovascular health, researchers found.

In a nationally representative study, getting less than 6 hours of sleep each night was associated an increased likelihood of having congestive heart failure (OR 1.67), MI (OR 2.05), and stroke (OR 2.01), according to Rohit Arora, MD, of the Chicago Medical School.

In addition, sleeping more than 8 hours was associated with greater odds of having coronary artery disease (OR 1.19) and angina (OR 2.07), Arora reported at the American College of Cardiology meeting here.

So it seems, he said at a press briefing, that the optimal amount of sleep is 6 to 8 hours.

The findings are consistent with prior studies that have identified relationships between the quality and duration of sleep and heart health.

A recent study of more than 140,000 participants showed that perceived sleep disturbance on at least three nights out of the week was associated with obesity, diabetes, MI, coronary artery disease, and stroke.

A 2008 study showed a relationship between shorter sleep duration and an indicator of coronary artery disease. In that study, each additional hour of sleep was associated with a 33% lower likelihood of coronary artery calcification.

And a large Norwegian study found that people who had trouble falling or staying asleep appeared to have an elevated risk of MI.

Arora and colleagues performed a retrospective analysis of data from more than 3,000 people older than 45 who participated in the National Health and Nutrition Examination Survey (NHANES) from 2007 to 2008.

After adjustment for several potential confounders, including age, systolic blood pressure, gender, body mass index, diabetes, smoking status, total cholesterol, HDL cholesterol, obstructive sleep apnea, and family history of heart attack, getting less than 6 hours of sleep each night was associated with greater odds of heart failure, MI, and stroke -- but not coronary artery disease or angina -- compared with getting 6 to 8 hours of sleep.

Sleeping more than 8 hours each night was associated with greater odds of coronary artery disease and angina, but none of the other outcomes.

Although an observational study cannot prove cause and effect, there are possible mechanisms through which getting too little sleep may worsen cardiovascular health, according to Arora and colleagues.

Shorter sleep duration has been tied to hyperactivation of the sympathetic nervous system, glucose intolerance, increased cortisol levels, increased blood pressure, decreased variability in heart rate, disruption of the hypothalamic axis, and increased inflammation.

A possible mechanism for the relationship between too much sleep and cardiovascular outcomes is less clear, but Arora said that it could be that patients who are sleeping for more than 8 hours a night have more underlying coronary artery disease and angina, more comorbid conditions like chronic obstructive pulmonary disease or diabetes, or socioeconomic circumstances that cause them to sleep longer.

The researchers acknowledged some limitations of the analysis, including the retrospective design, the possible influence of recall bias, and the lack of information on sleep quality.

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