A recent article, published in the Lancet Public Health, analysed trends over time regarding the incidence and prevalence of dementia, as well as its risk factors. Prevalence refers to the number of cases of dementia in a specific population at a particular time point or over a specified period of time while incidence refers to the rate of new cases of dementia occurring in a specific population over a particular period. The study by Karen de Sola-Smith and others is a systemic review, which included cohort studies that adjusted their data for age to take into account population ageing. Most existing cohort studies included in the review were from high-income areas such as Europe, Japan and the United States. The review found that the incidence of dementia is decreasing in most high-income countries, and the overall prevalence is either stable or declining. However, there were some differences among regions - for example, no decline in prevalence was found among farmers in France.
The authors explain that this general decrease in dementia incidence has been accompanied by an increase in rates of education and a decline in smoking rates, across high-income countries. Their calculations show an association between reduced smoking, better education and the decrease in dementia incidence. They also found that over time, diabetes, hypertension and obesity have contributed more (in relative terms) to dementia risk, with hypertension having the largest effect in most study populations. The authors postulate that compulsory education policies and measures to discourage smoking have beneficially impacted the incidence and prevalence of dementia. However, they also highlight a growing concern about cardiovascular health issues and their link to dementia risk. Some limitations of this study include the lack of ethnically diverse study populations and the fact that the review focuses mostly on high-income countries. Low-income countries may exhibit different trends regarding dementia. Additionally, the studies included in the review are at least ten years old, making it hard to know how trends may have changed recently.
https://www.thelancet.com/journals/lanpub/article/PIIS2468-2667(24)00120-8/fulltext