Sichun Gu ¹ Xiao-Lei Yuan ¹ Ping Yin ¹ Yuan-Yuan Li ² Chang-De Wang ³ Min-Jue Gu ¹ Li-Min Xu ¹ Chen Gao ¹ You Wu ¹ Yu-Qing Hu ¹ Canxing Yuan ¹ Yang Cao ³ Qing Ye ^1*

• ¹ Department of Neurology, Longhua Hospital, Shanghai, China
• ² Ruijin Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai, Beijing, China
• ³ Shanghai University of Traditional Chinese Medicine, Shanghai, Shanghai Municipality, China

Background: The association between body mass index (BMI) and rapid eye-movement (REM) sleep-related behavioral disorder (RBD) in Parkinson’s disease (PD) remains unknown. Our study was to investigate the association of BMI with RBD in PD patients. Methods: In this cross-sectional study, a total of 1115 PD participants were enrolled from Parkinson's Progression Markers Initiative (PPMI) database. BMI was calculated as weight divided by height squared. RBD was defined as the RBD questionnaire (RBDSQ) score with the cutoff of 5 or more assessed. Univariable and multivariable logistic regression models were performed to examine the associations between BMI and the prevalence of RBD. Non-linear correlations were explored with use of restricted cubic spline (RCS) analysis. And the inflection point was determined by the two-line piecewise linear models. Results: We identified 426 (38.2%) RBD. The proportion of underweight, normal, overweight and obese was 2.61%, 36.59%, 40.36% and 20.44%, respectively. In the multivariate logistic regression model with full adjustment for confounding variables, obese individuals had an odds ratio of 1.77 (95% confidence interval: 1.21 to 2.59) with RBD compared with those of normal weight. In the RCS models with three knots, BMI showed a non-linear association with RBD. The turning points of BMI estimated from piecewise linear models were of 28.16 kg/m2, 28.10 kg/m2, and 28.23 kg/m2 derived from univariable and multivariable adjusted logistic regression models. The effect modification by depression on the association between BMI and RBD in PD was also found in this study. Furthermore, the sensitivity analyses linked with cognition, education, and ethnic groups indicated the robustness of our results. Conclusion: The current study found a significant dose-response association between BMI and RBD with a depression-based difference in the impact of BMI on RBD in PD patients. Keywords: body mass index; rapid eye movement sleep behavior disorder; Parkinson’s Disease; Parkinson's Progression Markers Initiative; restricted cubic spline.