Cognitive impairment is a major problem in elderly persons. The possible role of nutrition in the development of cognitive disorders and dementia is a current theme of investigation. This paper discusses a number of possible associations between nutrition and cognitive function, especially hypotheses concerning deficiencies of B vitamins and homocysteine and damage caused by free radicals, along with the potential role of antioxidants in preventing such damage. We present putative mechanisms through which diet could modulate cellular life in the brain, along with practical advice for clinicians.