Different risks of early-onset and late-onset Parkinson disease in individuals with mental illness.

We aimed to investigate the association of various mental illnesses, including depression, bipolar disorder, schizophrenia, insomnia, and anxiety, with the risk of early-onset Parkinson's disease (EOPD) (age <50 years) and compare it with that of late-onset PD (LOPD) (age ≥50 years). This nationwide cohort study enrolled 9,920,522 people who underwent a national health screening examination in 2009, and followed up until 31 December 2018. There was a significantly increased risk of EOPD and LOPD in individuals with mental illness, and EOPD showed a stronger association than LOPD (EOPD, hazard ratio (HR) = 3.11, 95% CI: 2.61‒3.72; LOPD, HR = 1.70, 95% CI: 1.66‒1.74; p for interaction <0.0001). Our results suggest that people with mental illnesses aged < 50 years are at a higher risk of PD than those aged ≥50 years. Future studies are warranted to elucidate the pathomechanism of EOPD in relation to mental illness.