Summary: As populations age around the world, Alzheimer's disease and other types of dementia are becoming a rapidly growing public health problem. However, even at a very advanced age, it is possible to be entirely cognitively able or to have only mild cognitive impairment (a state of eumenia). Several factors determine how our brains will age. Some of them cannot be modified (genetic and family conditions, age, gender), and those that we can significantly influence (obesity, hypertension, diabetes, depression, social isolation, hearing impairment, brain injuries, lack of physical activity, lack of education, alcohol abuse, smoking, and air pollution). The latter group also includes deficiencies of some vitamins, especially B vitamins (thiamine, pyridoxine, cobalamin, folic acid) and vitamin D. Older people are a particular group at risk of inappropriate vitamin status. It is essential to bear it in mind, assess vitamin levels in people at risk of deficiencies, and correct them appropriately. It may significantly reduce the number of dementia cases in society.