Brain health

Brain health refers to how well the brain's abilities, including memory, reasoning, language and attention, are maintained across the lifespan, and to the absence of diseases that impair them. The main such disease in older age is dementia, a decline in mental abilities severe enough to interfere with daily life, most often caused by Alzheimer's disease or damage to the brain's blood vessels. About 57 million people were living with dementia worldwide in 2019, a number projected to reach 153 million by 2050 [1]. Dementia risk factors include age and genes, but the 2024 Lancet Commission on dementia attributed 45.3% of cases worldwide to 14 factors that could potentially be changed, among them high blood pressure, hearing loss, high LDL cholesterol (the cholesterol that builds up in artery walls), smoking, physical inactivity and social isolation [1]. In the SPRINT MIND trial of 9,361 adults, intensive blood pressure treatment reduced mild cognitive impairment (memory or thinking problems short of dementia) by 19% [2].

Short of dementia, mental abilities change gradually with age. Cognitive aging is measurable from midlife: in the Whitehall II study of British civil servants, memory, reasoning and verbal fluency (how readily words come to mind) scores declined over ten years in every age group from 45 to 70, while vocabulary did not [3]. Differences between people are often expressed as a cognitive or brain age in years; in one study of over 10,000 adults, a habitual 4-hour night of sleep was equivalent to 8 years of cognitive aging [4]. Most of these estimates come from snapshot studies that show association rather than cause.

Hearing and vision loss link the senses to the brain. More than 25% of people over 60 worldwide have disabling hearing loss [5], and in a US study adults with severe hearing loss had 4.94 times the dementia risk of those with normal hearing [6]. Among older adults with cataract (clouding of the eye's lens) or glaucoma (an eye disease that damages the optic nerve), cataract surgery was associated with 29% lower dementia risk [7]. Many brain health factors overlap with heart health, sleep and physical activity, which are covered in their own sections of the wiki.