UK research allays fears over dramatic increases in dementia incidence

Research conducted in the UK has found a 20% drop in the incidence of dementia over the past 2 decades, leading to an estimated 41,000 fewer cases per year in people aged 65 years and older than previously expected.

This means that "even in the presence of an ageing population the numbers of people estimated to develop dementia in any year has remained relatively stable, providing evidence that dementia in whole populations can change", say Carol Brayne (Cambridge University, UK) and fellow Cognitive Function and Ageing Studies (CFAS) collaborators.

They also note in Nature Communications that the drop in incidence was driven by a greater reduction among men at all ages above the age of 65 years.

The team carried out baseline screening interviews with 7635 individuals aged 65 years and over in 1989 to determine information including sociodemographic variables, lifestyle, health, ability to carry out activities of daily living and cognition. A sample of these individuals also completed an assessment interview including the full Geriatric Mental State examination and Mini Mental State Examination.

The participants, who were from five geographical areas of England and Wales, were then reassessed 2 years later, at which time the response rate was 76% of those still alive.

Using the same sampling methods and approach, 7762 new individuals from three of the original geographic areas were interviewed in 2008, with 74% of those still alive re-assessed in 2011.

Between the 2 decades, the incidence rates of dementia fell from 20.0 per 1000 person-years to 17.7 per 1000 person-years.

This was largely due to an overall 40% decrease in men, primarily in those aged 80 years and over, whereas there was no significant change in women.

The researchers estimate that there are just under 210,000 incident cases of dementia per year; 74,000 in men and 135,000 in women.

"This represents a far smaller increase than would have been expected from extrapolation of earlier estimates", they write.

The researchers point out that according to previous models, the population incidence of dementia in the UK was estimated to be 183,000 per year in 1991 and 251,000 per year in 2015 based on no change in the incidence rates and the known increase in the older population.

But based on their new estimated incidence rates, dementia would be expected to develop in just 209,600 people per year.

They do acknowledge, however, that within the UK and Europe, their reported reductions will be offset by earlier detection and diagnosis of dementia, meaning individuals who previously would not have been diagnosed will be in the future.

Brayne and colleagues put their findings down to improvements in brain health, particularly among men, and the primary prevention of dementia through healthier lifestyles, reduced vascular risk and enhanced opportunities for medical engagement. But they add that deprivation is still putting people at a disadvantage.

Brayne told the press: "The UK in earlier eras has seen major societal investments into improving population health and this appears to be helping protect older people from dementia. It is vital that policies take potential long term benefits into account."

By Lucy Piper

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