Consumption of milk and other dairy products and incidence of Parkinson’s disease: a prospective cohort study in French women

Abstract Previous studies on dairy products and Parkinson’s disease (PD) were inconsistent; a meta-analysis suggested that dairy increased risk in men only. Due to the long prodromal PD phase, reverse causation represents a major threat to investigations of diet in PD. We investigated associations between intake of milk and other dairy products with PD incidence, while considering reverse causation, in the E3N cohort study (1993–2018). PD diagnoses were validated using medical records and drug claim databases. Diet was assessed via a validated dietary questionnaire. Hazard ratios for incident PD were estimated using multivariable Cox regression models. Exposures were lagged by 5y in main analyses and longer lags in sensitivity analyses. We also examined the impact of adjustment for premotor symptoms. During a mean follow-up of 18.8y, 845 of 71,542 women developed PD. PD incidence increased significantly with pure milk consumption (HR/1-SD = 1.08, 95% CI = 1.02–1.14, P-linear = 0.011). A U-shaped relation was observed for milk added to coffee/tea (P-quadratic = 0.036), with lower PD incidence in women with moderate consumption (HR = 0.77 [0.61–0.97], P = 0.029) and no difference between non-drinkers and those with the highest consumption (HR = 0.98 [0.79–1.22], P = 0.878). Findings were similar in analyses using longer lags and adjusted for constipation/depression. Consumption of other dairy products was not associated with PD. Reverse causation is unlikely to explain the association of pure milk intake with increased PD incidence in women. There was a U-shaped relation for added milk, possibly explained by caffeine intake, and no association for other dairy products. Further studies are warranted to elucidate the underlying mechanisms.