Dementia Risk Factors: Hypertension, Obesity, and Diabetes Most Prevalent

Hypertension, obesity, and diabetes have become the most prevalent dementia risk factors over the decades, according to the findings of a study published in The Lancet Public Health.

Rates of dementia have declined from 1990 to 2019 in high-income countries (HICs).

To comprehensively examine the population-level factors that relate with declining dementia rates, researchers from the University College London in the United Kingdom searched publication databases through March 2024 for systematic reviews of cohort studies that assessed dementia rates over time. Using the reference lists from the reviews, data from those cohort studies as well as from population-based samples were included in this analysis.

The primary outcome was the change in dementia rates on the basis of population attributable fractions (PAFs) of associated risk factors.

This study included 27 studies retrieved from 5 systematic reviews. The papers evaluated the trends in dementia prevalence (48%), incidence (37%), and both prevalence and incidence (15%). The studies about prevalence were conducted in the United States (US; n=5), Sweden (n=5), the United Kingdom (UK; n=2), Japan (n=3), Spain (n=1), and France (n=1) and the studies about incidence were conducted in the US (n=6), Sweden (n=3), the UK (n=2), France (n=1), the Netherlands (n=1), Japan (n=1), and Nigeria (n=1).

The reporting about the prevalence of dementia was conflicting, for example, studies conducted in the US reported that dementia was increasing, was stable, and was decreasing, depending on the location, population, and publication year. Conversely, all studies evaluating dementia incidence reported declining rates, however, rates of decline differed substantially between studies.

Data were sufficient in 15 studies to calculate PAFs for dementia risk.

The general trends were the PAFs for dementia risk associated with less education and/or smoking were declining over time whereas the PAFs for dementia risk associated with obesity, hypertension, and/or diabetes were increasing over time.

The only study with sufficient data for a detailed PAF analysis was the Framingham study, which was conducted in the US between 1997 and 2013.

The weighted PAF for having a lower than high school education decreased from 5.5% between 1977 and 1983 to 3.7% between 1986 and 1991 and to 2.5% between 1992 and 1998.

The weighted PAF for smoking decreased from 4.2% to 3.0% between the earlier and middle time periods, respectively. Between 1986 to 1991 and 1992 to 1998, the incidence of dementia decreased by 38% and between 1992 to 1998 and 2004 to 2008, decreased by 44%.

This study could not assess reverse causality between risk factors and dementia.

“[C]ardiovascular risk factors might have contributed more to dementia risk over time, and so these risk factors deserve more targeted action for future dementia prevention efforts,” the researchers noted.

They concluded, “Levels of education have increased in many HICs, resulting in the PAF for this risk factor decreasing over time. Smoking levels have also declined in Europe and the USA due to reduced social acceptance of the practice, increasing costs, reduction in advertising, and bans on smoking in public places in many countries, also resulting in reduced PAF. These patterns suggest population-level interventions for risk factors for dementia could have substantial effects.”