If that doesn't sound like good news, it's because you haven't heard what they found next.

Researchers from Korea University Ansan Hospital and collaborators then found that among those RLS patients, those who were treated with a recently-developed dopamine agonist treatment experienced a protective buffer against Parkinson's disease onset.

The findings were gathered from a nationwide cohort of nearly 20,000 people, involved Ansan Hospital, Pohang Stroke and Spine Hospital, and National Health Insurance Service Ilsan Hospital, and were published online in the journal JAMA Network Open on October 6th, 2025.

Restless legs syndrome (RLS) is a common neurological sleep disorder characterized by an uncontrollable urge to move the legs, often worsening at night. Parkinson's disease, a progressive neurodegenerative disorder, is marked by tremor, rigidity, and slowed movement. Both conditions are associated with dysfunction in the brain's dopaminergic system, but their causal relationship has remained unclear.

This retrospective cohort study, led by Professor Jong Hun Kim from the Department of Neurology, Ansan Hospital, analyzed data from the Korean National Health Insurance Service Sample Cohort (2002–2019). The researchers identified 9,919 individuals with RLS and compared them with an equal number of matched controls without the condition.

Over a median follow-up of 15 years, Parkinson's developed in 1.6% of RLS patients compared with 1.0% of controls, confirming a heightened risk. When analyzed by treatment status, the results revealed a striking divergence.

Patients with untreated RLS showed the highest Parkinson's incidence (2.1%) and an earlier onset of the disease, whereas patients given a dopamine agonist treatment showed a markedly lower Parkinson's incidence (0.5%) and a delayed onset compared with controls.

"These findings indicate the existence of 'heterogeneity within RLS' which allows for multiple interpretations," Professor Kim explained. "One of the interpretations is that restless legs syndrome may serve as an early clinical marker for Parkinson's disease, particularly among untreated individuals."

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"Our results also indicate that dopamine therapy, used for symptom control, may confer protective benefits to the brain's motor pathways."

To strengthen the validity of their conclusions, the team employed target-trial emulation methods, an advanced analytical approach that reduces bias in observational research. This methodological rigor reinforces the biological plausibility of a link between RLS and PD rather than a mere overlap in symptoms.