Are dementia rates falling?

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By Dr Laura Phipps | Tuesday 17 September 2013

Alzheimer’s Research UK’s most recent study of dementia prevalence estimated around 820,000 people in the UK to be living with dementia, with that figure expected to rise dramatically. But researchers at the University of Cambridge have been re-evaluating these estimates, revealing intriguing and potentially important changes in dementia rates over the last few decades.

Dr Fiona Matthews announced findings from the UK-based multicentre study at the Alzheimer’s Association International Conference 2013 in Boston this July, showing that the estimated number of people with dementia in the UK should be lowered from previous predictions. This finding was unexpected, prompting discussion as to why and what it could mean for us all.

The study

Let’s start with what they did. The team studied two groups, or ‘cohorts’ of over 65s, those who were over 65 in the early 1990s and those who were over 65 in 2008. They looked to see how many had dementia and extrapolated the findings from both groups to estimate the number of people who should have had dementia in 2011. The figure calculated from the newer cohort sat at 670,000, rather than the 800,000 predicted from studying the older group.

A similar finding has also been reported in Sweden, from two groups of over 75s living in an affluent area of Stockholm followed between 1987 and 2008. This research suggested fewer new cases of dementia in this population over the course of the study.

Of course, every study has limitations and estimating dementia rates is a difficult task. Estimates can be influenced by many factors including:

  • Participant dropout
  • The characteristics of the population being studied
  • The accuracy of the data being used for the calculations.

All of these can cause estimates to vary between studies. However, we shouldn’t be quick to disregard these observations as a technical blip.

Possible explanations

The volunteers in the UK research who were studied between 1989 and 1994 were born into a different era to those reaching 65 after the turn of the century. Each cohort will have experienced similar life events, been exposed to similar social trends, and lived through the same changes in public health practice and education. However, these experiences and exposures will have differed between the two generational groups. It seems that those born later may have had a lower risk of dementia, although prevalence still varied widely across the country.

Risk factors

While age is the biggest risk factor for dementia, we know that there are others, including:

  • Poor cardiovascular health
  • High blood pressure
  • Lack of exercise
  • Diabetes
  • Obesity
  • Smoking
  • Alcohol consumption
  • Poor diet
  • High cholesterol
  • Low education.

Could changes in these factors be influencing dementia prevalence in current generations?

Incidence and mortality of cardiovascular disease has dropped in high income countries since the 1980s and risk factors such as high blood pressure are being more aggressively managed than in previous decades. Levels of education are also higher than they were several decades ago. Trying to tease out the specific factors that could explain this observation isn’t easy, but something that Dr Matthews and colleagues are keen to follow up.

Looking to other countries

Looking at changing trends in other countries could also provide some clues. In the 1970s, Finland was experiencing the highest cardiovascular disease mortality rates in the world. In response to aggressive public health campaigns, cholesterol levels fell dramatically (mainly due to changes in diet), blood pressure levels dropped and fewer people smoke now than four decades ago. As a result, cardiovascular disease mortality has dropped five-fold since 1970. They have also had success in diabetes prevention studies, and are now investigating whether dementia rates will also fall.

The findings from this, and other prevention studies under way across the world, will provide important insight into how improvements in public health could be influencing dementia risk.

Looking to the future

Although estimating dementia rates has its technical challenges, the take-home message from these findings should be positive. They suggest that there could be things we can actively do to influence our individual risk of developing dementia. However, as a population, we should still be concerned.

With an ageing population, the numbers of people with dementia will still remain very high and new patterns in public health could also threaten to buck this positive trend for future generations.

In Finland, despite dramatic improvements in cardiovascular health, blood pressure and cholesterol levels are on the rise again. Body mass index, diabetes rates and alcohol consumption are also increasing.

Concerns have already been raised about rising obesity levels in the UK and the impact this could have on dementia rates in the future, so we cannot afford to take our finger off the pulse now.

Learn more about research into risk factors by exploring our virtual dementia lab.

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Dr Laura Phipps