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Warnings of a dementia epidemic may be unfounded

Friday 21 August 2015

"Dementia may not be the fast-growing epidemic it has been painted to be," The Guardian reports. Latest data from Europe shows the percentage of dementia cases have levelled off, rather than increased.

However, as the elderly population is growing, the actual number of people with dementia will continue to rise, though perhaps not to the levels of a "dementia epidemic", as previously predicted. 

What is the basis for these reports?

This headline, among others, was prompted by a new "Policy View" article published in the peer-reviewed medical journal, The Lancet: Neurology.

The article looks at five cohort studies assessing the prevalence of dementia over the decades in the UK, Netherlands, Spain and Sweden. It was written by researchers from the University of Cambridge, the University of Newcastle, and institutions in Sweden, Germany and Spain.

The researchers found evidence dementia rates may not be increasing, as had been predicted, but are remaining stable – and could even be falling. 

What did the researchers do?

The researchers analysed the results of five cohort studies comparing dementia rates from the 1970s to 1990s with those done at least seven years later. Only studies with past and more recent dementia estimates that could be directly compared with each other were included.

These cohort studies involved similar older age adults at different time points in the following places:

  • Cambridgeshire, Nottingham and Newcastle in the UK
  • Stockholm and Gothenburg in Sweden
  • Zaragoza in Spain
  • Rotterdam in the Netherlands

For example, in the UK, the study looked at the prevalence of dementia in a random sample of 7,635 adults aged 65 and over who were followed up from 1990-95, comparing this with a similarly random sample of older adults who were followed up from 2008-11. This study adjusted the results to take age, sex and social deprivation into account.

This comparison study from the UK was the largest, with the others ranging from 707 to 7,528 people. The Spanish research compared cohort studies that were conducted with the shortest time gap between them – just seven years – whereas others, such as the Gothenburg study, spanned three decades. The age range for the studies was 55-70 at the start of the cohorts. 

What were the results?

The overall prevalence of dementia measured in the UK from 2008-11 was nearly a fifth (22%) lower than the prevalence from 1990-93. In the 1990 cohort, the prevalence for men and women was 8.3%, compared with 6.5% in the later study (ratio 0.7; 95% confidence interval [CI] 0.6 to 0.9).

There was no significant change in the overall prevalence of dementia in the other four comparison studies. However, the prevalence of dementia in men from Spain reduced by more than half from 5.8% to 2.3% (ratio 0.4, 95% CI 0.3 to 0.7).

In each country the prevalence of dementia approximately doubled with every five years of increasing age. 

What do the results really mean?

The researchers say the results suggest a possible decrease in the occurrence of dementia. They say this may be the result of prevention and health promotion policies aimed at reducing the risk of dementia, such as the stop smoking campaigns seen in recent decades.

While this is possible, the study relies on the results of cohort studies, which cannot prove cause and effect. In addition, this was not a systematic review of all the available evidence on the rates of dementia, but focused on a select number of studies, which limits the interpretation of the findings.

This study's strengths include that it picked studies that used the same study methods between two points in time to measure a change in dementia prevalence. But this has the downside of restricting the evidence to only those that fulfil this criteria – in this review it was just five studies. There may be other studies providing more accurate estimates of dementia at single points in time. These would not have been included here.

We should not take this study to mean that UK dementia prevalence rates are definitely in decline. The results tentatively suggest they might, as well as highlighting the need for more accurate and up-to-date information on dementia prevalence, and to constantly challenge the assumption that the prevalence of the disease is rising. Only good data will settle the debate.

It is important that we don't get complacent about the potential toll dementia could take on public health. While some risk factors, such as smoking, are in decline, others – particularly obesity – may lead to an upsurge in cases. 

How can you reduce your risk of dementia?

Strategies you can take to reduce your risk of dementia include:

  • stopping smoking (if you smoke)
  • being physically active
  • maintaining a healthy weight
  • having a diet that includes plenty of fruit and vegetables
  • keeping your blood pressure under control

Read more about how to prevent dementia

Analysis by Bazian
Edited by NHS Website

Links to the headlines

Dementia not the epidemic it was feared to be, say academics

The Guardian, 21 August 2015

Dementia levels 'are stabilising'

BBC News, 21 August 2015

Middle-aged winning battle against dementia, Cambridge University study finds

The Daily Telegraph, 21 August 2015

Warnings of dementia epidemic could be overblown, admit scientists

The Independent, 21 August 2015

Dementia epidemic fears 'out of date' as healthier lifestyles stabilise numbers with disease.

Daily Mirror, 21 August 2015

Dementia levels 'stabilising' across UK and Europe, study finds

ITV News, 21 August 2015

Links to the science

Wu Y, Fratiglioni L, Matthews FE, et al.

Dementia in western Europe: epidemiological evidence and implications for policy making

The Lancet: Neurology. Published online August 20 2015