Objectives/Aims Parkinson’s disease (PD) is associated with low religiosity cross-sectionally. Whether low religiosity might be associated with an increased risk for developing PD is unknown.

This study investigated whether low religiosity in adulthood is associated with increased risk for developing PD.

Methods A population-based prospective cohort study was conducted. Participants from the English Longitudinal Study of Aging (ELSA) and the Midlife in the United States (MIDUS) study who were free from PD at baseline (2004–2011) and completed questionnaires on self-reported religiosity, were included in a pooled analysis. Incident PD was based on self-report. Multivariable logistic regression was used to estimate odds ratios (OR) for developing PD according to baseline religiosity, with adjustment for sociodemographic characteristics, health and lifestyle factors and engagement in religious practices.

Results Among 9,796 participants in the pooled dataset, 74 (0.8%) cases of incident PD were identified during a median follow-up of 8.1 years. In the fully adjusted model, compared with participants who considered religion very important in their lives at baseline, participants who considered religion not at all important in their lives had a 10-fold risk of developing PD during follow-up (OR, 9.99; 95% CI, 3.28–30.36). Moreover, there was a dose-response relationship between decreasing religiosity and increasing PD risk (P <0.001 for trend). These associations were similar when adjusting for religious upbringing and when cases occurring within the first two years of follow-up were excluded from the analysis. The association was somewhat attenuated when religious practices were removed from the model as covariates, though it remained statistically significant (OR for ‘not at all important’ vs ‘very important’, 2.26; 95% CI, 1.03- 4.95) (P <0.029 for trend).

Conclusions This longitudinal study provides evidence for the first time that low religiosity in adulthood may be a strong risk factor for developing PD.