Reply: Is conscientiousness related to the risk of Parkinson’s disease?

We thank Drs. Luca, Nicoletti, and Zappia for their comment on our finding that neuroticism is a risk factor for Parkinson’s disease (PD)¹. We agree that obsessive-compulsive personality disorder (OCPD) is an important clinical condition to consider in the context of PD. Beyond neuroticism, OCPD is conceptually and empirically linked to conscientiousness², one of the five major personality traits. Conscientiousness is defined as a tendency to be cautious, responsible, hard-working, orderly, self-disciplined, scrupulous, and adherent to norms and rules. To an extreme, conscientiousness can lead to perfectionism, workaholism, rigidity, excessive control, and compulsive behaviors that characterize patients with OCPD. Similar conscientiousness-related traits are often used in anecdotal accounts and clinical observations of individuals with PD, which have led to the idea of a parkinsonian personality³. This overlap in definitions and clinical observations raises the fascinating hypothesis that extreme scores on conscientiousness could be a shared vulnerability that increases the risk for both OCPD and PD.

The above hypothesis, however, conflicts with a large and robust literature that has found high conscientiousness to have widespread protective health effects. From early in life, highly conscientious individuals refrain from health risk behaviors, are more likely to be physically active, have better cardiometabolic and inflammatory profiles, and are at lower risk of chronic conditions, including neurodegenerative diseases like Alzheimer’s disease and related dementias⁴. This literature supports the hypothesis that high conscientiousness could be protective for PD. Consistent with this hypothesis are cross-sectional findings that patients with PD and impulsive-compulsive behaviors score low on conscientiousness⁵. While informative, the available evidence from clinical samples do not provide a direct test for risk/protective factors because of potential changes during the preclinical and clinical stages of PD.

Surprisingly, there are no prospective studies that have tested conscientiousness as a risk/protective factor for incident PD (none of the studies in our meta-analysis¹ included conscientiousness). This is a significant gap in the literature that longitudinal studies should address in future research.