Known protective factors for Parkinson disease (PD) tend to have additive or superadditive effects, so that PD risk is very low in individuals with multiple protective risk factors, according to a recent study. Researchers derived risk scores among 69,968 women in the Nurses' Health Study (NHS) (1984–2012) and 45,830 men in the Health Professionals Follow-up Study (HPFS) (1986–2012). Risk scores were computed for each individual based on the following factors previously associated with PD risk: total caffeine intake, smoking, physical activity, and family history of PD for the NHS, and additionally total flavonoid intake and dietary urate index for the HPFS. 1,117 incident PD cases were documented during follow-up. They found:
- The adjusted hazard ratios comparing individuals in the highest category of the reduced risk score to those in the lowest category were 0.33 in the NHS and 0.18 in the HPFS.
- Additive interaction was present between no family history of PD and caffeine in men and between caffeine and physical activity in women.
Kim IY, O’Reilly ÉJ, Hughes KC, et al. Integration of risk factors for Parkinson disease in 2 large longitudinal cohorts. [Published online ahead of print April 11, 2018]. Neurology. doi:10.1212/WNL.0000000000005473.