An international study spanning 14 countries shows that while dementia risk factors differ between populations, they consistently cluster together, offering new evidence to guide more effective and locally adapted prevention strategies.
Study: Differences in the prevalence and patterns of dementia risk factors across 14 countries and regions: a harmonised cross-national analysis. Image credit: izzuanroslan/Shutterstock.com
A large international study published in The Lancet Healthy Longevity found that while the prevalence of modifiable dementia risk factors differs widely between countries, these risk factors frequently occur together and form similar clusters across diverse populations.
Existing dementia evidence overlooks important population differences
The prevalence of dementia is projected to triple by 2050 as the global population ages, making effective prevention strategies an increasing public health priority. Alongside aging, the most recent Lancet Commission report identified 14 modifiable risk factors that together account for an estimated 45% of dementia cases, including low education, high LDL cholesterol, physical inactivity, smoking, diabetes, and hypertension.
However, much of the evidence underpinning these estimates comes from high-income countries (HICs), raising questions about how well the findings apply to low- and middle-income countries (LMICs), where sociodemographic, economic, and healthcare conditions can differ substantially. Although previous studies have estimated population-attributable fractions (PAFs) for dementia in individual countries, and some cross-country analyses have been conducted, these have often relied on data from relatively small geographic areas and have provided limited insight into how risk factors are distributed or occur together across diverse populations.
The tendency for dementia risk factors to co-occur has helped drive the development of multidomain prevention strategies, including the Finnish Geriatric Intervention Study to Prevent Cognitive Impairment and Disability (FINGER) and the worldwide FINGER network. However, broader comparative evidence is needed to determine whether these approaches can be adapted across different settings or whether new prevention strategies are required.
To address this gap, the current study mapped the prevalence and patterns of 12 established modifiable dementia risk factors using harmonized data from 214,251 adults aged 50 years or older across 11 nationally representative population-based studies spanning 14 countries and regions with diverse income levels and stages of development.
Large cross-national analysis examines modifiable dementia risks
In this comparative cross-sectional study, researchers analyzed harmonized data from 11 nationally representative aging studies spanning 14 countries and regions. They primarily used the most recent study wave, which included a refresher sample, to provide representative and up-to-date population estimates, although older waves were used for some individual risk factors when comparable data were unavailable.
The analysis examined the prevalence of 12 of the 14 modifiable dementia risk factors identified by the Lancet Commission, with traumatic brain injury and air pollution excluded because consistent data were not available across the studies.
Dementia risk profiles differ across global populations
The prevalence of individual dementia risk factors varied markedly across countries, although low education, hypertension, and smoking consistently ranked among the most common. Low education emerged as the leading risk factor in nine of the 14 countries and regions studied, with hypertension and smoking ranking among the top three in almost every setting.
Clear differences also emerged between high- and low-income settings. Low education was substantially more common in several LMICs, affecting 85.6% of participants in China compared with 12.0% in the United States. Furthermore, for eight of the 11 risk factors examined by education level, prevalence was significantly higher among people with low education in at least half of the countries or regions with available data. The authors suggest that low educational attainment may contribute to the development of other downstream risk factors, highlighting its importance as a target for prevention strategies.
By contrast, obesity was more prevalent in HICs, affecting 44.9% of participants in the United States compared with 13.3% in India. Social isolation, which was defined as living alone to enable harmonized comparisons across studies, also ranked more highly in HICs than in many LMICs.
Age-related patterns were more consistent across settings. Adults aged 70 years or older were more likely than those aged 50–69 years to have most of the dementia risk factors examined, with the main exceptions being smoking, excessive alcohol consumption, and obesity.
Dementia risk factors vary differently between women and men
The prevalence of many risk factors also differed according to sex across countries, but no consistent trend was observable. For instance, women were less likely than men to have diabetes in the Irish study but more likely than men to have diabetes in the Brazilian study. Men were more likely to be smokers or drink in excess in LMICs, but women were almost universally more likely to be depressed or socially isolated.
Educational differences were also different by sex for many risk factors. Thus, they were greater among women with diabetes, obesity, and other cardiovascular risk factors for dementia.
Such variation, by education and gender, could help design targeted interventions and help to trace interactions that determine how risk factor exposure occurs. For instance, poor socioeconomic status may influence employment, access to healthcare or community services, and thus affect dementia risk.
Multiple dementia risks commonly occur together
Despite these differences, dementia risk factors commonly co-occurred. Across every country and region studied, more than half of participants had at least two modifiable dementia risk factors, while in 11 of the 14 countries and regions, more than 20% had at least four. After accounting for differences in the number of risk factors measured in each study, the average proportion of available risk factors present was highest in Mexico and Brazil, followed by China, the United States, and Northern Ireland.
Co-occurrence might be due to common or downstream mechanistic pathways or disease determinants, helping to target the most influential or upstream component. According to the authors, this picture may partly explain why single-factor interventions are often relatively ineffective.
Similar dementia risk clusters span high- and low-income countries
Although the prevalence of individual risk factors differed between countries, they rarely occurred in isolation. Across all countries and regions studied, more than half of participants had at least two modifiable dementia risk factors, and in 11 of the 14 countries and regions, more than 20% had at least four. After accounting for differences in the number of risk factors measured in each study, the greatest overall burden of co-occurring risk factors was observed in Mexico and Brazil, followed by China, the United States, and Northern Ireland.
The researchers suggest these patterns reflect shared biological pathways and common upstream influences, such as socioeconomic disadvantage, that contribute to multiple dementia risk factors simultaneously. This clustering may help explain why interventions targeting a single risk factor often produce only modest benefits. Instead, identifying groups of related risk factors could allow prevention strategies to focus on the most influential upstream drivers or to address several interconnected risks simultaneously, potentially improving overall effectiveness.
Cross-sectional design limits causal interpretation
The study analyzed only the 12 Lancet Commission dementia risk factors for which comparable data were available. Binary versions were used for all risk factors, but continuous measures could yield more detailed information. Inconsistency in data remained despite efforts to harmonize it, possibly due to differences in survey design, cultural adaptation, data collection, and interpretation.
Much of the data was self-reported or based on self-reported physician diagnoses, and some survey waves dated back to 2009, which could introduce bias. The researchers also simplified some complex concepts, such as defining social isolation by living alone, to improve comparability across countries.
Because this was a cross-sectional study, it could identify patterns of prevalence and co-occurrence but could not determine causal relationships between risk factors or establish whether cluster-based interventions would reduce dementia risk. Compared to PAFs, this study does not consider effect size.
Even so, the prevalence of risk factors and their distribution allow for better policy and intervention planning by providing insight into future population-level impact and the feasibility of interventions. It also allowed the researchers to collate risk factor data from a wider range of countries irrespective of dementia prevalence or effect size variations.
Shared risk clusters could improve dementia prevention worldwide
The findings underline the importance of obtaining comparative evidence on dementia risk factors across countries, though they also indicate the difficulties inherent to this task. Where country-specific evidence is unavailable, findings from settings with similar levels of development may help guide the adaptation of existing interventions, while still accounting for local social, healthcare, and policy contexts.
The researchers conclude that even though risk factors differ in prevalence between countries and populations, universal frameworks could be designed for dementia prevention that take advantage of common elements while allowing for adaptation to country-specific differences.
Moreover, the existence of clusters of risk factors that occur together indicates that interventions addressing several risk factors simultaneously may be applicable across diverse settings, although dedicated cluster-informed trials are needed to determine whether this approach improves outcomes.
Although a one-size-fits-all approach would not succeed, general patterns, combined with country-specific data (when available), can be used to ensure that the design of dementia policies and interventions is based on high-quality quantitative evidence.
