People who sleep for less than six hours a night may have an increased risk of developing hardening of the arteries compared to those who sleep for seven or eight hours per night, the results of a new study indicate.

Previous research has found that a lack of sleep can raise the risk of cardiovascular disease by increasing risk factors such as blood pressure and obesity.

This latest study looked at almost 4,000 people in Spain, with an average age of 46 years. They were divided into four groups:
-Those who slept less than six hours each night
-Those who slept six to seven hours
-Those who slept seven to eight hours
-Those who slept more than eight hours.

All underwent detailed heart tests.

The study found that after traditional risk factors for heart disease were taken into account, those who slept for less than six hours a night were 27% more likely to have atherosclerosis than those who slept for seven or eight hours a night.

Atherosclerosis, also known as hardening of the arteries, occurs when plaques build up in the lining of the arteries. These plaques are made up of a number of substances, such as cholesterol and cellular waste products.

If an artery becomes too narrow, it cannot supply adequate blood to organs and tissues, which can lead to major health problems such as a heart attack or stroke.

The study also found that those who had a poor quality of sleep were 34% more likely to have atherosclerosis than those who had a good quality of sleep.

The quality of sleep was determined by how often a person woke during the night, and the frequency of movements during sleep, which reflect the sleep phases. All participants wore an actigraph, which is a small device that continuously measures activity or movement, in order to measure their sleep.

The researchers pointed out that ‘shorter sleep duration that is of good quality can overcome the detrimental effects of the shorter length'.

They also noted that alcohol and caffeine consumption tended to be higher in participants with short and disrupted sleep.

"Many people think alcohol is a good inducer of sleep, but there's a rebound effect. 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," they said.

When it comes specifically to coffee, the researchers said that genetics are key.

"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," they commented.

Meanwhile, the researchers also noted that while the number of participants who slept for more than eight hours a night was small, women who slept for more than eight hours a night appeared to have an increased risk of atherosclerosis.

"Cardiovascular disease is a major global problem, and we are preventing and treating it using several approaches, including pharmaceuticals, physical activity and diet. But this study emphasises we have to include sleep as one of the weapons we use to fight heart disease - factor we are compromising every day.

"This is the first study to show that objectively measured sleep is independently associated with atherosclerosis throughout the body, not just in the heart," commented the study's senior author, Dr José M. Ordovás, director of nutrition and genomics at the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University in the US.

Details of these findings are published in the Journal of the American College of Cardiology.