Dementia is a strongly age-related syndrome due to cognitive decline that can be considered a typical example of the combination of physiological and pathological aging-associated changes occurring in old people; it ranges from intact cognition to mild cognitive impairment, which is an intermediate stage of cognitive deterioration, and dementia. The spread of this syndrome has induced to study and try to reduce dementia modifiable risk factors. They include insulin resistance and hyperinsulinaemia, high blood pressure, obesity, smoking, depression, cognitive inactivity or low educational attainment as well as physical inactivity and incorrect diet, which can be considered one of the most important factors. One emerging strategy to decrease the prevalence of mild cognitive impairment and dementia may be the use of nutritional interventions. In the last decade, prospective data have suggested that high fruit and vegetable intakes are related to improved cognitive functions and reduced risks of developing a neurodegenerative process. The protective effects against neurodegeneration could be in part due to the intake of flavonoids that have been associated with several health benefits such as antioxidant and anti-inflammatory activities, increased neuronal signaling, and improved metabolic functions. The present article is aimed at reviewing scientific studies that show the protective effects of flavonoid intake against mild cognitive impairment and dementia.