Highlight
- Over 15 years in Australia, the combined modifiable population attributable fraction (PAF) of dementia risk remained stable (~47% in mid-life and ~51% in late-life) despite shifts in individual risk factors.
- Mid-life saw reductions in smoking, high alcohol use, physical inactivity, hearing loss, and low education, but increases in obesity, depression, and poor diet.
- Low-income groups and males exhibited higher modifiable dementia risk, with depression becoming the leading mid-life risk factor by 2022, disproportionately impacting females and those in lower socioeconomic strata.
- Findings underscore the need for targeted, multidomain preventive interventions to reduce socioeconomic and sex disparities in dementia risk.
Study Background
Dementia is a growing global public health challenge characterized by progressive cognitive decline impairing daily functioning and quality of life. Estimated to affect over 55 million people worldwide, the disease imposes substantial social and economic burdens. Importantly, research suggests that up to 45% of dementia cases may be attributable to potentially modifiable risk factors, including lifestyle and medical comorbidities. Timely identification and modification of these risk factors are key to reducing dementia incidence at the population level.
In Australia, demographic aging alongside socioeconomic disparities necessitates ongoing surveillance of risk factor prevalence to optimize targeted prevention. However, little longitudinal population-level data has described sex and socioeconomic differences in modifiable dementia risk factors, or their evolving contributions over time. The present analysis aims to fill this gap by tracking 15-year trends in twelve established modifiable dementia risk factors and calculating respective population attributable fractions (PAFs) across Australian national health surveys, stratified by sex, income, and life-stage.
Study Design
This investigation is a cross-sectional time series analysis utilizing data from five nationally representative Australian health surveys conducted between 2007-08 and 2022. Twelve modifiable dementia risk factors were analyzed: low education, hypertension, obesity, high cholesterol, smoking, high alcohol intake, poor diet, physical inactivity, hearing loss, depression, diabetes, and social isolation.
The analysis included two age-defined cohorts: mid-life (45-64 years) and late-life (65-84 years). Socioeconomic status was categorized by household income, defined as low income (lowest 40%) versus high income (highest 60%). Prevalence rates for each risk factor were calculated annually, adjusted prevalence ratios were estimated, and combined PAFs were computed to characterize the proportion of dementia risk attributable to modifiable factors within defined population subgroups.
Key Findings
Sample sizes across surveys ranged from 4100-5589 for mid-life and 2799-3762 for late-life participants, ensuring robust population representation.
In mid-life, significant trends included reductions in smoking, high alcohol consumption, physical inactivity, hearing loss, and low education prevalence. Conversely, obesity, depression, and poor dietary habits increased. Despite these opposing shifts, the combined PAF remained statistically unchanged—47.2% (95% CI 46.5-48.0) in 2007-08 versus 46.9% (45.9-47.7) in 2022.
Among late-life adults, decreases were observed in high alcohol intake, physical inactivity, and low education prevalence, while depression and poor diet showed upward trends. The overall combined PAF also remained stable at 51.5% (50.9-52.5) in 2007-08 and 51.4% (50.7-52.4) in 2022.
Notably, modifiable dementia risk in mid-life was distinctly higher among males compared to females, and in lower-income households compared to higher-income counterparts. By 2022, depression emerged as the leading modifiable risk factor in mid-life, disproportionately affecting women and individuals in low-income groups, highlighting a critical target for intervention.
The observed stability in total PAF masks dynamic changes in individual risk profiles, which have shifted toward mental health and metabolic risk factors amid declines in traditional risks such as smoking and physical inactivity.
Expert Commentary
These findings align with international literature emphasizing the persistent burden of modifiable dementia risk factors, while highlighting the shifting epidemiology of risk. The emergence of depression as a predominant risk factor among mid-life adults, especially women and socioeconomically disadvantaged populations, underscores the growing recognition of mental health’s role in cognitive decline.
This evolving risk profile suggests the need for multidomain dementia prevention strategies integrating mental health, metabolic, and lifestyle interventions. The disproportionate burden on low-income groups further signals the necessity of health equity-focused policies.
Limitations of the study include reliance on self-reported survey data prone to recall bias and inability to establish causal relationships. Additionally, the cross-sectional design precludes assessment of individual-level longitudinal risk trajectories. Nonetheless, the repeated cross-sectional approach provides valuable population-level trend insight.
Future randomized controlled trials or longitudinal cohort studies should investigate whether tailored interventions addressing depression and metabolic risk in vulnerable mid-life groups can effectively reduce dementia incidence.
Conclusion
Over the past 15 years, modifiable dementia risk in Australia has remained relatively stable in population attributable impact but evolved in constituent components. Traditionally dominant risks such as smoking and physical inactivity have decreased, whereas depression, poor diet, and obesity have increased. Low-income households and males bear a greater modifiable risk burden in mid-life, with depression increasingly prominent among women and disadvantaged groups.
These findings advocate for dynamic, targeted multidomain prevention initiatives accounting for sex and socioeconomic disparities to reduce dementia incidence. Addressing evolving mental health and metabolic risk factors may be critical for future public health strategies.
Funding
National Health and Medical Research Council (NHMRC).
References
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