Restless legs syndrome (RLS), a pesky condition that triggers leg spasms when fatigued, may actually not be as innocent as previously imagined. New research shows that men that had the condition were 40 percent more likely to die earlier than those without it.

The study was published in the journal Neurology by Xiang Gao, a research scientist at the Harvard School of Public Health. The researchers said about five to 10 percent of U.S. adults have the condition.

"It brings recognition to RLS, which is largely unrecognized and under-diagnosed." Gao said in a statement. "It suggests the importance to further understand (the condition)."

The study followed more than 18,000 men in their late 60s or older for eight years and found that among 690 with restless leg syndrome, 171, or 25% of the men with the disorder, died in that period. Fifteen percent without RLS died.

One of the authors of those studies, András Szentkirályi, a research fellow at Germany's Semmel University's Institute of Behavioral Sciences, says he "questions the results," noting the previous four studies looked at a general population while Gao's study focused on a narrower group, Szentkirályi says he would "exercise caution if the most recent study is to be applied to the general population."

"Even with these differences, I was surprised that there were such strong relations between RLS and mortality," he says. "There still is no explanation for these findings or how to further treat it. ... We need more research."

RLS is also considered a sleep disorder, as it causes an uncomfortable sensation described at  itchy, "pins and needles", which can interfere with sleep.