Fewer people develop dementia – but researchers do not know why

Breaking new ground 30. okt 2021 3 min Postdoctoral fellow Emilie Rune Hegelund Written by Kristian Sjøgren

Fewer people in Denmark are being diagnosed with dementia today than previously. The reasons remain unclear, but researchers are striving to determine how to reduce the incidence of dementia further.

Since 2004, the number of people developing dementia in Denmark has declined substantially.

A new study reveals that the incidence of dementia in Denmark declined by 23% among men and 34% among women.

Some of this may result from demographic changes, but even accounting for this, the incidence of dementia has declined by about 20%.

The study also shows that improvements in traditional risk factors for dementia have contributed to reducing the incidence in Denmark, but even these cannot explain the decline. There must be some other explanation, but researchers have not found it yet.

“We have identified some modifiable risk factors that may prevent dementia, but they do not explain the entire recent decline. We therefore need to think outside the box to determine why fewer people develop dementia today than previously so that we can accelerate these trends and enable a further decline,” explains a researcher behind the new study, Emilie Rune Hegelund, postdoctoral fellow, Section of Epidemiology, Department of Public Health, University of Copenhagen.

The research has been published in Alzheimer’s & Dementia.

Dividing a cohort according to risk factors

Emilie Rune Hegelund and colleagues examined data from Statistics Denmark to identify 1.8 million people 65 years and older who lived in Denmark at any point from 2005 to 2018.

They then used data from the Danish National Patient Registry, the Danish Psychiatric Central Research Registry and the Danish National Prescription Registry to identify individuals who had developed dementia during the study period. The researchers also mapped these people’s education level, household wealth, prescription drug use and whether they had experienced a stroke and used this to create four risk domains covering many of the well-established modifiable risk factors for dementia.

  • Education. Higher educational attainment is associated with a lower risk of dementia.
  • Wealth. Individuals with higher household wealth or income have a lower risk of dementia.
  • Cerebrovascular health. Whether a person has had a stroke generally indicates a person’s cerebrovascular health, which is negatively associated with developing dementia.
  • General health. Prescription drug use indicates general health, and a person’s risk of developing dementia is associated with poor general health.

“The 2020 Lancet Commission on Dementia Prevention, Intervention and Care published a life-course model of how to prevent dementia based on 12 risk factors, and we summarised these traditional modifiable risk factors in four risk domains. We then categorised the study population into low, medium and high in three of the domains, and cerebrovascular health was based on stroke versus no stroke. We did this for each year and simultaneously examined whether individuals in each year had been diagnosed with dementia,” says Emilie Rune Hegelund.

Risk factors alone cannot explain the decline

The results show that the declining incidence of dementia cannot solely be attributed to the fact that the high-risk group is doing better today than before. Even the low-risk group has experienced a declining incidence of dementia since 2005.

In addition, this research shows that the four risk domains alone cannot explain the decline in the incidence of dementia, so something else must underpin this societal trend.

The researchers examined the various birth cohorts and found that the decline primarily resulted from 65-year-olds and 75-year-olds developing dementia less often than 65-year-olds and 75-year-olds in the past.

The result remained valid even when the researchers considered the four risk domains.

“So something about these younger birth cohorts unrelated to the traditional risk factors has reduced their risk of dementia,” explains Emilie Rune Hegelund.

Even fewer people with dementia in the next generation?

Emilie Rune Hegelund speculates that more physical activity and people taking better care of their brains may be why fewer people develop dementia.

“Maybe people are getting better at keeping their body and brain going than they used to be. Far more older people exercise today than before,” says Emilie Rune Hegelund, adding that it will be interesting to see whether the decline in dementia continues.

“Today’s 65-year-olds have a lower risk of developing dementia than the current 85-year-old cohort did in the past, and this is independent of the traditional risk factors. It will be exciting to see whether the present generation of 45-year-olds will also have a lower risk in 20 years, even though we may still not be able to explain why,” says Emilie Rune Hegelund.

Striving to discover the causes

According to Emilie Rune Hegelund, the perspective in the new study is that the researchers have confirmed that some modifiable risk factors for developing dementia are associated with the risk of developing dementia in Denmark, but they cannot entirely explain the positive downward trend.

Researchers and doctors therefore need to continue thinking outside the box to identify the unknown factors that appear to prevent dementia.

“If we find these factors, they can potentially be used to determine how to reduce the incidence of dementia further. The problem now is that we are doing something right but do not really know what it is,” concludes Emilie Rune Hegelund.

"The plasticity of late-onset dementia: A nationwide cohort study in Denmark" has been published in Alzheimer's & Dementia. In 2018, the Novo Nordisk Foundation awarded a Challenge Programme-grant to co-author Rudi Westendorp for the project Harnessing the Power of Big Data to Address the Societal Challenge of Ageing.

Research at the Department of Public Health contributes to the scientific foundation for improving the health of the population and for increased insi...

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