Incidence and Prevalence of Dementia: Global Shifting Trends and the Role of Risk Factors

In recent years, studies have shown a mixture of declining and rising trends in the prevalence and incidence of dementia across different regions, reflecting alterations in contributing risk factors. Researchers, led by Naaheed Mukadam and colleague Frank J. Wolters, conducted a comprehensive review and analysis, published in Lancet Public Health, detailing these complex patterns that bear significant implications for public health policies globally.

The review encompassed data from prior population-based cohort studies that consistently employed identical methods across various waves, with the aim to also gauge changes in dementia risk factors over time using population attributable fractions (PAFs). Their search yielded five systematic reviews that ultimately led to the inclusion of 27 relevant studies covering Europe, the USA, Japan, and Nigeria.

Results from these studies highlighted divergent regional trends. While Europe and the USA reported a consistent decline in dementia incidence, one study from Japan indicated an uptick in both prevalence and incidence of dementia. Meanwhile, Nigeria reported stable incidence rates.

Diving deeper into the influence of specific risk factors, the team observed a general reduction in PAFs for less education or smoking, pointing to a decrease in these factors' contribution to dementia over time. In contrast, PAFs associated with obesity, hypertension, and diabetes showed an upward trend.

The Framingham study from the USA provided a substantial data set that linked the decline in dementia incidence to decreased PAFs for lack of education and smoking, among other factors. However, there was an appreciable rise in hypertension, obesity, and diabetes PAFs, raising concerns over their potentially growing influence on dementia trends.

This extensive review underscores the vital importance of lifestyle interventions and country-level policies aimed at reducing risk factors for dementia, especially in terms of education and smoking. The inconsistent findings across different studies, however, point to the need for further research in this area, particularly in low and middle-income countries where the incidence of dementia is escalating.

Funded by the National Institute for Health and Care Research Three Schools’ Dementia Research Programme, this work is open access and can be read in full in the Lancet Public Health (2024; 9: e443–60).

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