People who sleep less than six hours a night may be at an increased risk of cardiovascular diseases compared to those who sleep for seven to eight hours, according to a study.
The study, published in the Journal of the American College of Cardiology, found that poor quality sleep increases the risk of atherosclerosis -- plaque buildup in the arteries throughout the body.
"Cardiovascular disease is a major global problem, and we are preventing and treating it using several approaches, including pharmaceuticals, physical activity and diet," said Jose M Ordovas from the Centro Nacional de Investigaciones Cardiovasculares Carlos III (CNIC) in Spain.
"But this study emphasises we have to include sleep as one of the weapons we use to fight heart disease -- a factor we are compromising every day," said Ordovas, who is also associated with Tufts University in the US.
This is the first study to show that objectively measured sleep is independently associated with atherosclerosis throughout the body, not just in the heart, researchers said.
Previous studies have shown that lack of sleep raises the risk of cardiovascular disease by increasing heart disease risk factors such as glucose levels, blood pressure, inflammation and obesity, they said.
The new study included 3,974 bank employees in Spain and used imaging techniques to detect the prevalence and rate of progression of subclinical vascular lesions in a population with an average age of 46 years.
All participants were without known heart disease and two-thirds were men. All participants wore an actigraph, a small device that continuously measures activity or movement, for seven days to measure their sleep.
They were divided into four groups: those who slept less than six hours, those who slept six to seven hours, those who slept seven to eight hours and those who slept more than eight hours.
The participants underwent 3D heart ultrasound and cardiac CT scans to look for heart disease.
The study found that when traditional risk factors for heart disease were considered, participants who slept less than six hours were 27 per cent more likely to have atherosclerosis throughout the body compared with those who slept seven to eight hours.
Similarly, those who had a poor quality of sleep were 34 per cent more likely to have atherosclerosis compared with those who had a good quality of sleep.
Quality of sleep was defined by how often a person woke during the night, and the frequency of movements during the sleep which reflect the sleep phases.
"It is important to realise that shorter sleep duration that is of good quality can overcome the detrimental effects of the shorter length," Fuster said.
The study also suggested sleeping more than eight hours a night may be associated with an increase in atherosclerosis.
While the number of participants who slept more than eight hours was small, the study found women who slept more than eight hours a night had an increased risk of atherosclerosis.
Alcohol and caffeine consumption were higher in participants with short and disrupted sleep, the study found.
"Many people think alcohol is a good inducer of sleep, but there's a rebound effect," Ordovas said.
"If you drink alcohol, you may wake up after a short period of sleep and have a hard time getting back to sleep. And if you do get back to sleep, it's often a poor-quality sleep," Ordovas said.
While some studies show drinking coffee can have positive effects on the heart, Ordovas said it can depend on how quickly a person metabolises the coffee.
"Depending on your genetics, if you metabolise coffee faster, it won't affect your sleep, but if you metabolise it slowly, caffeine can affect your sleep and increase the odds of cardiovascular disease," he said.
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