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.