Diet and common neurological disorders: cohort studies on dementia, Parkinson’s disease, and stroke

Abstract: Risk factors for dementia, Parkinson’s disease, and stroke have been widely studied but there are still research gaps concerning the role of diet for the development of these diseases. The overall aim of this thesis was to investigate whether various aspects of diet are associated with common disorders and diseases in the brain. Paper I and II are based on the Uppsala Longitudinal Study of Adult Men (ULSAM). Paper III and IV are based on the Swedish Mammography Cohort (SMC) and the Cohort of Swedish Men (COSM). In paper I, we investigated the associations between three different dietary patterns and incidence of Alzheimer’s disease (AD), dementia, and cognitive impairment. We observed no associations between adherence to the Healthy Diet Indicator and any of the outcomes studied, or between adherence to a Mediterranean-like diet (mMDS) and AD or dementia. There was a tendency towards a lower risk of cognitive impairment with higher adherence to the mMDS, and a weak association between adherence to a Low Carbohydrate High Protein score and higher risk of all-type dementia. Overall, there were no strong associations with the studied dietary patterns and development of dementia or cognitive impairment. In paper II, we found no associations of vitamin D measured as vitamin D intake, plasma 25-hydroxyvitamin D concentrations, or a vitamin D synthesis genetic risk score with incident AD, vascular dementia, dementia, or performance in the Mini-Mental State Examination.In paper III, we observed a weak higher risk of PD associated with milk consumption but there was no dose-response relationship. Thus, this association needs to be interpreted with caution. Fermented milk intake was not associated with PD.In paper IV, we found that a higher long-term milk consumption based on repeated measures of intake was not associated with total stroke, weakly and non-linearly associated with lower risk of cerebral infarction and higher risk of hemorrhagic stroke. Fermented milk consumption was not associated with any stroke type. Our results highlight the importance of repeated measurements of food intake, separate analyses of milk and fermented milk consumption, and to study stroke types separately.Despite the lack of strong associations, the findings of this thesis have increased our knowledge about the potential role of overall diet, vitamin D, and milk and fermented consumption in the prevention or development of common neurodegenerative diseases and stroke.