Dementia

Dementia is an insidious, chronic, and progressive loss of a previously acquired cognitive ability, in contrast to delirium, which is an acute confusional state. ^[1] Mild cognitive impairment is the symptomatic predementia stage on the continuum of cognitive decline, characterized by objective impairment in cognition that is not severe enough to require help with usual daily activities. ^[2] Recognized Alzheimer's disease-related dementias include Alzheimer's disease, dementia with Lewy bodies, frontotemporal dementia, vascular dementia, and mixed dementias, which commonly share cerebrovascular dysfunction at some point in the disease process. ^[3]

In vascular dementia, cerebral small vessel disease characterised by arteriolosclerosis, lacunar infarcts, microinfarcts, and diffuse white matter changes has gained prominence as an important substrate of cognitive impairment. ^[4] Sleep disturbance can contribute to cognitive decline and may increase the risk of Alzheimer's disease dementia by increasing beta-amyloid burden through systemic inflammation, in a bidirectional relationship. ^[5] The glymphatic system that clears the brain of protein waste products is mostly active during sleep and degrades with age, suggesting it may be a therapeutically targetable final common pathway in neurodegenerative dementias. ^[6]

In a meta-analysis, the age-standardized prevalence of dementia in those aged 60 years and over was 5% to 7% in most world regions, higher in Latin America (8.5%) and distinctly lower in sub-Saharan Africa (2% to 4%). ^[7] Among community dwellers aged 50 and over, the pooled prevalence of all-cause dementia was 697 per 10,000 persons and was greater in women than in men (788 versus 561 per 10,000). ^[8] The prevalence of Alzheimer's disease in Europe was estimated at 5.05%, and was higher in women (7.13%) than in men (3.31%). ^[9]

In 2010, 58% of all people with dementia lived in countries with low or middle incomes, a proportion anticipated to rise to 71% by 2050, with major implications for social and public policy. ^[7] Around a third of dementia cases are attributable to modifiable risk factors such as physical inactivity, smoking, and hypertension, and exercise has emerged as a key intervention for reducing the risk of age-related cognitive decline and dementia. ^[10] In a systematic review and meta-analysis, vaccination against herpes zoster was associated with a reduced risk of any dementia (risk ratio 0.76) and of Alzheimer's disease (risk ratio 0.53). ^[11]