Can Parkinson’s disease be prevented? Epidemiological evidence on lifestyle factors

The etiology of Parkinson’s disease (PD) is largely unknown, but epidemiological studies have provided robust evidence that environmental factors have a central role in PD pathogenesis and progression. The studies included in this thesis examined associations between several lifestyle factors and subsequent risk of PD.

In study I, we prospectively investigated the association between physical activity and risk of PD in a Swedish cohort of 43,368 men and women. We found that higher levels of physical activity were associated with lower risk of PD. In addition, when pooling our results and all previously prospective cohort studies on this topic using meta-analysis, there was a 34% lower risk of PD for the highest level of physical activity compared with the lowest level.

In the second study (study II), we examined the effect of Swedish moist smokeless tobacco (i.e. snus in Swedish) on future risk of PD using individual participant data from seven Swedish cohorts, consisting of 348,601 men. Our pooled results confirmed that non-smoking men who used snus had a substantially lower risk of PD compared with never snus users. In addition, a dose-response relationship between snus use and risk of PD was indicated.

A third series of analyses evaluated the effect of dietary antioxidants on PD risk (study III). Using comprehensive dietary information on 45,837 men and 38,937 women from two population-based cohorts, we concluded that intake of dietary vitamin E and β-carotene was associated with a lower risk of PD.

In the last study (study IV), we analyzed Swedish census data with more than 4.6 million individuals regarding the potential effect of socioeconomic status on PD risk, as well as all-cause mortality before and after PD diagnosis. PD risk was higher in individuals with higher socioeconomic status, and all-cause mortality was higher in individuals with lower socioeconomic status regardless of PD status. However, the impact of socioeconomic status on all-cause mortality was weaker in PD patients than in PD-free individuals.

In conclusion, our findings contribute to the existing epidemiological evidence on the associations between lifestyle factors and risk of PD. Our results from prospective cohort studies suggest that lifestyle factors can influence future risk of PD. Interventions on these lifestyle factors may have the possibility to prevent the disease eventually.

List of scientific papers

I. Yang F, Trolle Lagerros Y, Bellocco R, Adami HO, Fang F, Pedersen NL, Wirdefeldt K. Physical activity and risk of Parkinson's disease in the Swedish National March Cohort. Brain. Feb 2015;138(Pt 2):269-275.
https://doi.org/10.1093/brain/awu323

II. Yang F, Pedersen NL, Ye W, Liu Z, Norberg M, Forsgren L, Trolle Lagerros Y, Bellocco R, Alfredsson L, Knutsson A, Jansson JH, Wennberg P, Galanti MR, Lager A, Araghi M, Lundberg M, Magnusson C, Wirdefeldt K. Moist smokeless tobacco (Snus) use and risk of Parkinson's disease. International Journal of Epidemiology. Dec 2016.
https://doi.org/10.1093/ije/dyw294

III. Yang F, Wolk A, Håkansson N, Pedersen NL, Wirdefeldt K. Dietary antioxidants and risk of Parkinson's disease in two population-based cohorts. [Submitted]

IV. Yang F, Johansson AL, Pedersen NL, Fang F, Gatz M, Wirdefeldt K. Socioeconomic status in relation to Parkinson's disease risk and mortality: A population-based prospective study. Medicine. Jul 2016;95(30):e4337.
https://doi.org/10.1097/MD.0000000000004337