Hypertension and cognitive impairment in the elderly [Ipertensione arteriosa e decadimento cognitivo]

The prevalence and incidence of dementia is expected to exponentially increase in the future 30 years. Accordingly, the identification of the causes of dementia and of the possible risk factors become very important for researchers and clinicians. A growing body of evidence suggests that hypertension may be a risk factor for vascular and neurodegenerative dementias. Recently, it has been shown that hypertension is associated not only with cerebrovascular disease, which is in turn associated with dementia, but it could also affect the course of Alzheimer disease. A strong relationship between long-standing hypertension and cognitive impairment or dementia has been demonstrated by several large observational studies, especially with untreated hypertension. The risk increases with increasing blood pressure. However, the relationship between blood pressure and dementia is not linear. Blood pressure may decrease to normal or low levels before dementia (and especially Alzheimer's disease) becomes clinically manifest. There may also be an association between blood pressure variability in hypertensive patients and impaired cognition. In an extension of the Systolic Hypertension in Europe (Syst-Eur) study in older people and in other studies using the 24-hour non-invasive monitoring of the blood pressure values, an increased blood pressure variability at baseline has been shown to positively correlate with worse cognitive performances. This variability may reflect central nervous system dysregulation or occult injury to the prefrontal autonomic centers, occurring just before the clinical manifestation of dementia. Randomized therapeutic hypertension trials focusing on cognitive function and the occurrence of dementia have shown that an active treatment may be beneficial, although the optimal levels of blood pressure have not yet defined. Future studies, comparing the effect of different classes of antihypertensive drugs on the absolute blood pressure levels and of the 24 hour blood pressure variability, are expected to further clarify this topic.