Dementia is an acquired highly disabling syndrome common among elderly people. Alzheimer's disease is the most frequent type of dementia, and its prevalence is rapidly increasing due to the aging of populations. Therefore, the need to find effective preventive means is pressing. Population studies allow identification of risk/protective factors for dementia/Alzheimer's disease, thus leading to preventive strategies that can be implemented in the general population to reduce the incidence of this disorder. Presented here is an overview of the main findings of epidemiological studies on nutritional factors and nutrition-related pathological conditions, as related to dementia and Alzheimer's disease.