A scientist studying sleep patterns, attaches wires to a patient's head during an experiment in 2006. According to a study chronic sleep deprivation can do more than leave you short-tempered: it can also stress your heart and raise your risk of cardiovascular disease and death.[AFP]

The neurological and behavioural effects of long-term sleep loss have been well-documented, ranging from lowered concentration and hand-eye coordination to poor mood.

But the study by researchers at the University of Pennsylvania School of Medicine adds to a growing body of evidence that there is also a physiological price to be paid for insufficient time under the sheets.

The study found that a sleep deficit built up over just five nights can significantly stress the heart.

The researchers tested the cardiac function of their 39 volunteers twice -- once at the beginning of the study, after a night of 10 hours' sleep, and again after five nights when they got a mere four hours of shut-eye each night.

The electrocardiograms revealed that all of the volunteers had a much faster heart beat and significantly less heart rate variability following the nights of sleep deprivation.

Heart rate variability describes the naturally occurring beat-to-beat changes in heart rate which reflect the body's adjustment to a host of stresses and stimuli.

Reduced variability can be a marker for cardiac problems and other diseases and has been linked to high blood pressure.

"The effect of the sleep deficit was to increase the stress on the hearts of these volunteers," said Siobhan Banks, a lead author on the study.

"If our finding is sustained by a larger group and further analysis, it may suggest why short sleep duration is associated with a heightened risk of cardiovascular disease and mortality."

The findings are consistent with previous research showing that shift workers are at higher risk for cardiovascular disease due to the fact that they get less sleep because of the disruption in their circadian or sleep-wake rhythms.

Banks, an assistant professor at the University of Pennsylvania in Philadelphia, will present her study Wednesday at SLEEP 2007, the annual gathering of the Associated Professional Sleep Societies in Minneapolis, Minnesota.

In another study to be presented at the same meeting Wednesday, researchers reported that extra sleep can help athletes raise their game.

Investigators who tracked six men on the Stanford University basketball team found that the ball players were able to shave seconds off their sprint times and improve their shooting percentages by getting as much extra sleep as possible over an extended period of time.

The athletes also reported improved energy and improved mood during practices and games, according to the Stanford University investigators.