Men who jerked and flexed their legs involuntarily at night were more likely to develop cardiovascular disease in a new study of sleep and chronic disease in the 65-and-up crowd.
During a one-night sleep assessment, more than two-thirds of men had the involuntary movements, which usually occur in the foot or at the ankle or hip joint, and most of them woke up during the night because of it.
Those men had a higher risk of a combination of heart and blood vessel conditions, including heart attack, stroke, and blocked or ruptured arteries. Although those events happened over a few years after researchers measured nighttime leg movements, the study isn't proof that overactive limbs caused the heart problems, researchers said.
Still, "people have to keep an open mind into some other possible risk factors for these things," said Dr. Brian Koo, the study's lead author from Case Western Reserve University School of Medicine in Cleveland.
So-called periodic limb movements are considered a different condition from restless leg syndrome (RLS) — although many people with restless legs also move around involuntarily and unknowingly at night.
People with RLS feel an uncontrollable urge at night and during the day to move their legs, sometimes causing insomnia. Although it's been the subject of zealous disease awareness campaigns — and, some claim, disease mongering — RLS isn't considered a sign of a serious medical condition and symptoms may go away with lifestyle changes, such as relaxation, exercise, and avoiding caffeine.
In contrast to restless legs, many people who have periodic limb movements don't know about it, Koo said. One hint, though, is being very sleepy during the day — a result of many brief nighttime wake-ups. Sleep tests are needed to make the diagnosis, researchers said.
They estimate that between 5 percent and 8 percent of the U.S. general population experiences periodic limb movements and movements in the most severe cases may "number well into the hundreds each night."
For the current study, Koo and his colleagues gave single-night tests to close to 3,000 men age 65 and older. In the tests, researchers measured how frequently men had involuntary jerks and flexes and how often their sleep was interrupted by a quick arousal.
They found that 70 percent of the sleepers had those leg movements at least five times per hour while they slept and at least 60 percent woke up — without knowing it — at least once an hour.
Over the next four to five years, 500 of the men had a new case of heart disease, or a stroke or artery condition, the researchers report in Circulation.
The limb movements weren't linked to any one single event, such as heart attacks. But when all types of cardiovascular disease were combined, men with frequent leg movements had a 25 percent to 30 percent higher disease risk than men with no or few involuntary movements.
And those who had a lot of wake-ups during the night were 20 percent to 25 percent more likely to get cardiovascular disease than men who slept soundly.
Even though the researchers were able to take into account underlying diabetes and high blood pressure, plus how much men smoked and drank, the findings can't prove that anything about the nighttime behavior causes heart problems.
Still, they say it seems possible that the leg movements and arousals also come with increases in heart rate or blood pressure during sleep. And over enough repeated nights, that could drive up long-term heart-related risks.
The jerks and flexes are sometimes treated with medications for Parkinson's disease and anti-convulsants.
Koo said that more studies are needed before his team's findings should lead to any changes in diagnosis or treatment of involuntary nighttime activity.
"I don't think it would change the implications of management at this point," agreed Dr. Brian Murray, who studies sleep at Sunnybrook Health Sciences Center in Toronto and wasn't involved in the new paper.
"We need a further study to see if you treat these movements, would you decrease the risk of cardiovascular diseases?" he told Reuters Health. "At this point we don't have that evidence."
Murray added that because many people have leg movements at night, it's unclear how severe or frequent they have to be to warrant concern. Still, he said that research "continues to paint a picture that indeed the limb movements aren't as benign as we thought they were."
"There's still a lot that needs to be sorted out, but potentially sleep in general is important to look at in terms of cardiovascular risk," Koo told Reuters Health.
The study authors caution that the findings shouldn't be generalized to women, to men under 65, or to non-white men — since less than 10 percent of those in their study were minorities.
Dr. Fouzia Siddiqui, a sleep specialist at Rockingham Memorial Hospital in Harrisonburg, Virginia, pointed out that the sleep tests were done in people's homes, instead of in the lab where they may have been more precise. She called the study "a beginning" toward exploring a possible link between nighttime movements and cardiovascular disease.
She said that anyone who is concerned about their sleep shouldn't keep it to themselves.
"Disturbed sleep at night can predispose you to so many different disorders," Siddiqui, who didn't participate in the new research, told Reuters Health. "If it's interfering in your daytime function, there's definitely a need to talk to your physician," she said.
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