Most mental functions - memory, emotionality, and mental performance - are not greatly affected by age-related physiological changes, although the speed of thought is liable to decrease with age. In spite of the resilience of mental capacity, it remains dependent on brain cell function, which is contingent on adequate energy and oxygen intake, and a supply of important micronutrients.
Malnutrition is quite common in elderly people. However, it is possible for poor dietary habits in early and later adulthood to result in chronic degenerative brain diseases with impaired cognitive function. The ability of certain vitamin supplements to delay the development of degenerative diseases - e.g. vitamin E and Alzheimer disease - emphasizes the need for adequate nutrition throughout life.
Theoretically, dietary deficiencies might affect cognition by hastening the cellular aging process, by promoting chronic diseases, and by a direct action on cerebral function.
Oxidative stress is considered to be responsible for age-related degenerative changes in neurons and arterial endothelium cells, and lack of antioxidant nutrients has been shown to increase the incidence of cerebrovascular events. Vitamins C, E, B12 and folic acid may all exert a protective effect on this mechanism.
Nutritional supplements may have beneficial effects on the progress of chronic conditions in subjects who are not definitely deficient of such substances, but have nutrient intake within the lower limit of the normal range. Results from various sources (e.g. the Basel, Rotterdam and SENECA studies ) show a clear correlation between dietary intake and cognitive performance. Thus lifelong administration of antioxidant vitamins can offer some protection against neurodegenerative diseases, and thus maintain good mental functioning in the elderly.
Distinct vitamin deficiencies can occur in the older person. An obvious example is Wernicke's encephalopathy, due to low vitamin B1 intake in alcoholism. Vitamin B12, B6 or folic acid deficiencies have been associated with neuropsychiatric disorders such as depression and dementia, possibly due to neurotoxic effects of elevated homocysteine levels. Depressed patients with low folate levels have a poor response to antidepressant treatment.
Malnutrition is often associated with low plasma cholesterol levels, and cholesterol levels have been found to correlate with Mini-Mental State Examination (MMSE) scores. There are other studies that show improved cognitive performance correlating with higher plasma levels or dietary intake of B vitamins, folic acid and vitamin C. Clearly, the effects of prolonged suboptimal dietary intake of such micronutrients, and their nullification by supplements, prove that cognitive function is dependent on an adequate supply of important substances normally contained in a balanced, healthy diet.
