[Dementia and diabetes: casual or causal relationship?].

Several studies have reported the existence of an epidemiological association between diabetes mellitus (DM) and dementia. Although this association is more evident for vascular dementia, it is also described in Alzheimer's disease (AD). In this review we evaluate the different hypotheses that may explain the association between DM and dementia. We can consider the existence of a diabetes type 3 as the situation that occurs when hyperinsulinemia in response to insulin resistance leads to a decrease of the brain insulin and a poor regulation of insulin-degrading enzyme; thus, beta-amyloid accumulates, among other mechanisms, by the decline of its degradation by insulin-degrading enzyme. Consequently, AD may be related, at least in part, to a brain insulin resistance. There are several studies that prove the concept that a better metabolic control, especially in not very old people, is associated with an increased cognitive performance. It is not known whether the use of any specific drug for the treatment of DM is better than any other. It is important for physicians responsible for the metabolic control of diabetic patients to know this possible association, and to explore cognition in the control visits of patients with DM.