People with Restless Leg Syndrome have an almost three-fold higher risk of suicide, according to new research.
Doctors need to pay special attention to the mental health of patients with the condition, which causes an irresistible urge to move and can be worse at night time.
Up to one in 20 adults in the UK are affected by the syndrome, with it causing severe sleep deprivation in the worst cases.
The study of almost 170,000 individuals found those with RLS (Restless Leg Syndrome) were 2.7 times more likely to take their lives or self-harm, researchers found.
Corresponding author Professor Xiang Gao, an epidemiologist at Penn State University in the US, said: "It suggests restless legs syndrome isn't just connected to physical conditions, but to mental health, as well.
"And, with RLS being under-diagnosed and suicide rates rising, this connection is going to be more and more important.
"Clinicians may want to be careful when they are screening patients both for RLS and suicide risk."
In the US, suicide rates have risen by up to 30 percent since the turn of the century. In the UK, it is the single biggest killer of men under the age of 45.
Prof Gao said: "Suicide is a global health concern and is associated with multiple risk factors, including male sex, family history of suicide, childhood adversity, alcohol abuse, psychiatric disorders and sleep problems.
"Given sleep disturbance and depression are highly concurrent in individuals with RLS, it is plausible part of the elevated overall mortality risk associated with RLS maybe driven by increased risk of death from suicide."
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Prof Gao and colleagues said RLS affects about five percent of the US population. It may be caused low levels of brain chemical dopamine - which also controls movement.
Some studies linked it to high blood pressure, heart attacks and increasing mortality rates, and others to depression and suicidal thoughts.
He said he had accessed a data set with more than 200 million people, so he was able to test a hypothesis he'd wanted to for more than a decade.
His team compared health information on Americans with health insurance between 2006 and 2014 - 24,179 of whom had been diagnosed with RLS and 145,194 who had not.
The study, published in JAMA Network Open, found the former group had a 270 percent higher chance of suicide or self-harm.
Neither they, nor the control set, had any history of the behaviours before the tracking began.
The risk did not drop even after depression, sleep disorders and common chronic diseases such as diabetes were taken into account.
