The Risk of Suffering Dementia is Declining
Numerous epidemiological studies have shown that the risk of suffering dementia in later life is in decline, even as demographic aging of the population drives an increase in the overall incidence of age-related disease. Why is the individual risk of dementia declining? It is potentially a consequence of the broad use of statins to reduce the consequences of atherosclerosis, as well as ever greater attention given to control of blood pressure in later life. The state of the vasculature is an important contribution to the state of the aging brain, with a variety of different mechanisms involved. The brain is an energy-hungry organ, and blood flow and supply of nutrients declines with age. The blood-brain barrier becomes leaky with age, allowing inflammatory molecules and cells into the brain. Raised blood pressure results in increased pressure damage, such as rupture of small blood vessels in the brain. And so forth; cardiovascular health is important for many reasons.
In 2021, about 6.2 million U.S. adults aged 65 or older lived with dementia. Because age is the strongest risk factor for dementia, it has been predicted that increasing life expectancies will substantially increase the prevalence of Alzheimer's disease and related dementias from about 50 million to 150 million worldwide by 2050. However, there is growing evidence that age-adjusted dementia prevalence has been declining in developed countries, possibly because of rising levels of education, a reduction in smoking, and better treatment of key cardiovascular risk factors such as high blood pressure.
A new study employs a novel model to assess cognitive status based on a broad set of cognitive measures elicited from more than 21,000 people who participate in the national Health and Retirement Study, a large population-representative survey that has been fielded for more than two decades. The model increases the precision of dementia classification by using the longitudinal dimension of the data. Importantly for the study, the model is constructed to ensure the dementia classification is calibrated within population subgroups and, therefore, it is equipped to produce accurate estimates of dementia prevalence by age, sex, education, race, and ethnicity, and by a measure of lifetime earnings.
The prevalence of dementia in the United States dropped 3.7 percentage points from 2000 to 2016. The age-adjusted prevalence of dementia declined from 12.2 percent of people over age 65 in 2000 to 8.5 percent of people over age 65 in 2016 - a nearly one-third drop from the 2000 level. The prevalence of dementia decreased over the entire period, but the rate of decline was more rapid between 2000 and 2004. The study further found that education was an important factor that contributed, in a statistical sense, to the reduction in dementia, explaining about 40 percent of the reduction in dementia prevalence among men and 20 percent of the reduction among women.
Seems likely to me that the main reason for the decline is that more people are choosing to commit suicide rather than live with dementia.
Statins are almost certainly a big part of it:
https://alz-journals.onlinelibrary.wiley.com/doi/10.1002/trc2.12108
Most statins are associated with approximately a factor of two reduction in all neurodegenerative disorders. The worst (fluvastatin) is associated with almost no impact. The best (pitavastatin) is associated with more than a factor of four reduction in various disorders.
"Pitavastatin showed the strongest reduction in NDD incidence (RR, 0.21; 95% CI, 0.12-0.37; P < .001), followed by atorvastatin (RR, 0.38; 95% CI, 0.36-0.40; P < .001), rosuvastatin (RR, 0.48; 95% CI, 0.44-0.52; P < .001), ..."
One of the more interesting things is that pitavastatin is associated with a 10-20x reduction in alzhiemers risk. As far as I've been able to investigate, this could plausibly be due to a mix of pitavastatin having an unusually long serum half life, being lipid soluble, and being able to cross the BBB.