- Dementia numbers are increasing globally, but there is some evidence that incidence is declining.
- In order to maintain that decline, scientists need to know why it is happening.
- A global team of researchers has proposed that decreasing smoking rates and increasing education rates since the 1970s, particularly in high-income countries, could be behind the trend.
- They argue the link they found between smoking and education and the decline in dementia incidence, supports further public intervention over diabetes, high blood pressure, and obesity to further reduce dementia incidence.
Reduction in smoking and increases in education have been linked to reducing the incidence rate of dementia in some high-income countries.
Tackling other risk factors associated with dementia could be a way to ensure this decline continues, a group of researchers from Europe and the U.S. have said.
“There is a lot of interest around how to prevent dementia and we know many studies have found that dementia prevalence and incidence have declined over time. We thought it was important to look for studies examining changes in dementia rates and see whether we could link this with changes in dementia risk factors,” said first author Naaheed Mukadam, MD, PhD, professor of psychiatry at University College London, U.K. and consultant in the Mental Health Liaison Team at University College London Hospital.
“This could help guide public policy to reduce dementia rates further in the future,” he told Medical News Today.
The results of the study are published in The Lancet Public Health.
In 2020, some of these researchers had estimated that 40% of dementia cases were associated with 12 risk factors, which could potentially be minimized as part of the Lancet’s commission on dementia prevention, intervention, and care.
These were identified as:
- less education
- high blood pressure
- hearing impairment
- smoking
- obesity
- depression
- physical inactivity
- diabetes
- low social contact
- excessive alcohol consumption
- traumatic brain injury
- air pollution
Prior to that, data from a Global Burden of Disease Study (GBD) showed age-standardized incidence of dementia decreased in 71 of 204 jurisdictions between 1990–2019. Of the 18 jurisdictions that saw significant decreases, all except one — Venezuela — was a high-income country. While overall cases of people with dementia are increasing globally, this is due to an aging population, and researchers looked at the incidence of dementia within the population as a whole.
The researchers set out to determine if it would be possible to map changes in the exposure of the population to the risk factors they had identified over time. They carried out an analysis of the data provided for 27 review articles, which provided cohort data from 1947–2015. They compared data for dementia incidence and risk factor prevalence over time.
The researchers confirmed that incidence had declined in the U.S. and Europe. Overall, they showed dementia incidence had decreased by 44% between 1992–98 and 2004–08.
The researchers worked out how much of the proportion of disease or mortality would reduce in a population if everybody stopped smoking, for example. They showed that this had decreased over time.
Similarly, the health impact of the number of people not completing high school decreased over this time period, as more people completed their education.
“It is easier to agree with the author’s conclusion that decreases in smoking could be associated with a drop in the incidence of dementia more than an increase in education is associated with a drop in the incidence of dementia. Smoking cessation is a clear modifiable risk factor for cardiovascular Health and would directly decrease incidence of vascular dementia or multi-infarct dementia. An increase in education has never been proven to be neuroprotective or prevent college-educated people from getting dementia,” said Clifford Segil, D.O., neurologist at Providence Saint John’s Health Center in Santa Monica, CA, who was not involved in the research.
The authors said that the finding that public health interventions such as smoking and education could impact dementia incidence demonstrated that public health interventions for other risk factors were worth the investment.
Diabetes, high blood pressure, and obesity exposure all increased over the same time period, and this could be a target for future interventions, they added. High blood pressure was shown to be the highest dementia risk factor, but authors noted there have already been public interventions in many countries to reduce this.
“Our previous work has shown the promise of individual interventions but we want to move away from placing the responsibility on individuals to change their health and rather think about the population as a whole and how to create environments that can help improve population health,” Mukadam said.
“In many countries, there are already policies to increase compulsory education and reduce smoking and our study shows this is linked with a decline in dementia, so it is possible to have a positive impact,” he explained.
Looking at the benefits of making these interventions was something researchers wanted to do next, he added: “Cost savings of population level interventions to target dementia risk factors is another area of interest, as well as tackling inequalities in dementia prevention.”
Jurisdictions face significant financial costs in supporting people with dementia, and most social care infrastructure is not sufficient to meet demand. Interventions that could reduce the incidence of dementia could save significant amounts of money for many countries.
Population-wide health interventions also need strong evidence that they will work and a strong safety profile, as they will potentially be imposed on healthy people. Individual interventions also need strong evidence that they will do more harm than good.
“I think our emphasis on heart disease should be targeted to prevent stroke, heart attacks, and vascular dementia. In the year 2024, risk factors for Alzheimer’s dementia remain unclear, and there is no clear risk factor that can be targeted. Dementia affects well-educated and poorly-educated people, it affects high and low socioeconomic communities, and further research on dementia risk factors remains challenging because of our limited understanding of what is causing dementia patients to have cognitive changes and memory loss,” Segil said.
“The possibility that cardiovascular disease and obesity contribute to dementia may indeed lower the bar for possible intervention. If public Health interventions targeting these conditions can also reduce the risk of dementia, it adds further justification for their implementation. This dual benefit could encourage more comprehensive and aggressive public Health strategies, as the impact would extend beyond cardiovascular Health to also potentially mitigating the risk of dementia,” said Steve Allder, MD, consultant neurologist at Re:Cognition Health, who was not involved in the research.
“We have looked at public health interventions for obesity in another paper and found some promising results. We are not necessarily advocating for any one risk factor over another but need to think more broadly about using public health policy if possible rather than just telling people to look after their health,” added Mukadam.
