Cognitive effects of nutritional deficiency.

Deficiencies of various nutrients, primarily vitamins, impair cognition. The link is strongest for vitamin B12, thiamine, and niacin. Yet even for these, the role of mild "subclinical" or multiple deficiencies in the genesis of mental dysfunction is unclear. Most information in this field is based on animal studies often poorly applicable to the human condition or on clinical pathology complicated by advanced age, alcoholism, and intercurrent disease. There is a need for well controlled, double-blind, prospective trials to elucidate the cognitive effects of malnutrition.