New research suggests that restless leg syndrome is tied to heart and kidney problems.

Considered a neurological, sleep, or movement disorder, restless leg syndrome affects up to 1 in 10 people in the U.S. For those coping with a more severe form of RLS, countless sleepless nights--during which they may toss and turn constantly, or get up and pace the floor--can shatter quality of life.

Researchers from the Memphis VA Medical Center, the University of Tennessee Health Science Center, and the University of California at Irvine found that those with restless leg syndrome are at higher risk for stroke, heart and kidney disease, and earlier death. Some studies in the past had suggested such links, but the new research provides the strongest evidence yet.

For the study, researchers collected and analyzed data from about 3,700 veterans who were recently diagnosed with restless leg syndrome. They also selected about 3,700 veterans without the condition. The team then tracked the two patient groups for about eight years and compared their outcomes. Specifically, the researchers looked for new cases of stroke, coronary heart disease, chronic kidney disease, or death from any cause.

They found a fourfold higher incidence of stroke and heart disease in the restless leg syndrome group, and a threefold higher incidence of kidney disease. The gap in all-cause mortality between the groups was smaller, but the Veterans with restless leg syndrome were still 88 percent more likely to die during the follow-up period.

Importantly, the study doesn't show that RLS directly brings on any of the other conditions--only that there's an association. In fact, it could be that RLS may result, in part, from other underlying health conditions. There's also a genetic component: The condition, which can occur at any age, often runs in families and specific gene variants have been linked to it.

The authors, led by Dr. Miklos Z. Molnar at UT, mention several theories as to how the condition is possibly linked to other poor health outcomes. For example, the chronic loss of sleep itself could directly curb longevity. It could also help set the stage for heart disease, as well as other problems, such as diabetes or depression.

Researchers stress that their study proves nothing about cause and effect.

The findings are detailed in the Journal of Sleep Research.