New York, March 19 (IANS): Getting too much or too little sleep, may be bad for your heart, say researchers, adding that people who get seven or eight hours of sleep per night have less stiffness in their arteries, which is associated with a lower risk of developing heart disease or suffering a stroke.

"The message, based on our findings, is 'sleep well, but not too well.' Getting too little sleep appears bad for your health but too much seems to be harmful as well," said study lead author Evangelos Oikonomou from Yale University in the US.

For this analysis, researchers assessed sleep patterns in 1,752 people living in the Corinthia region of Greece using a standard questionnaire.

They ranged in age from 40 to 98 years, with a mean age of 64 years old

Participants were then divided into one of four groups based on self-reported sleep duration: normal (seven to eight hours a night), short sleep duration (six to seven hours a night), very short sleep duration (less than six hours a night) or long sleep duration (greater than eight hours a night).

At the time of the study, each participant also underwent ultrasound imaging to measure the thickness of the inner part of the arterial wall.

Thickening of the arterial walls reflects plaque buildup and is associated with an increased risk of stroke and other cardiovascular events.

The researchers found that even after accounting for other known risk factors for heart disease or stroke, people who slept less than six hours or more than eight hours a night had significantly greater odds of having plaque buildup in the walls of their carotid arteries--a 54 per cent and 39 per cent increase, respectively--compared with those who got seven or eight hours of shut eye.

The study adds to mounting evidence that sleep patterns, similar to diet and exercise, may play a defining role in someone's cardiovascular risk.

"We don't fully understand the relationship between sleep and cardiovascular health. It could be that sympathetic nervous system withdrawal or a slowing [of this system] that occurs during sleep may act as a recovery phase for [usual] vascular and cardiac strain," Oikonomou said.

"Moreover, short sleep duration may be associated with increased cardiovascular risk factors--for example, unhealthy diet, stress, being overweight or greater alcohol consumption--whereas longer sleep duration may be associated with a less active lifestyle pattern and lower physical activity," Oikonomou added.

The research is scheduled to be presented at the American College of Cardiology's Annual Scientific Session Together with World Congress of Cardiology on March 28-30 in the US.