Lifestyle risk factors for Parkinson disease and amyotrophic lateral sclerosis : an epidemiological perspective

Abstract: Following progressive aging of the population, the global prevalence of PD and ALS is expected to increase in the next decades. Primary prevention of the diseases is hampered by limited knowledge of preventable causes. Some suggestions have been made that an inactive lifestyle, obesity and dietary habits such as fat intake may have a role in the etiologies. Evidence is inconsistent regarding BMI and evidence is lacking regarding sitting time and different types of fat intake, and PD risk. The relationship between desired BMI and depression is not well explored. The prevalence of depression in ALS vary largely, and information about antidepression drug use in ALS patients is scarce. Little is known about depression prior to ALS. This thesis aims to investigate the association between sitting time, BMI and intake of dietary fat, and incident PD (study I-II), to describe discrepancies between current, ideal and desired BMI and explore its relation to depression (study III), and to investigate the association between depression and ALS, before and after ALS diagnosis (study IV). Study I-II were prospective cohort studies based on the Swedish National March Cohort, following 42 000 individuals and measuring exposures from a baseline questionnaire and outcome of incident PD from the National Patient Register. The highest quartile of saturated fat intake was associated with a 41% increased risk of PD compared to the lowest quartile (HR Q4 vs. Q1: 1.41; 95% CI: 1.04–1.90). No association was found between sitting time, BMI and PD. Study III was a population based study in Stockholm. About 10 000 participants filled in a questionnaire, investing desired BMI. In persons with obesity, large discrepancies between desired BMI and BMI 25 kg/m2 were predicted by male sex and high BMI, while large discrepancies between current and desired BMI were predicted by female sex, high BMI and depression. Study IV was a nested case control study and a matched cohort study based on a nationalwide samle of ALS patients. The risk of depression diagnosis or antidepression drug use was increased both the years before (multivariable adjusted OR 2.0, 95% CI: 1.7-2.2) and after (multivariable adjusted HR 13.5, 95% CI: 10.2-17.8) ALS diagnosis. Further research efforts are encouraged to understand the pathogenesis of PD and ALS with focus on modifiable risk factors.