While there is widespread fear of an explosion in dementia cases as the global population ages, there has actually been a downward trend in Europe and North America in the 2000s, and signs of a similar pattern emerging in Japan.
The reasons for that decline are hard to tease out but may be due to better management of cardiovascular conditions like high blood pressure and high cholesterol that are known to raise the risk of dementia in high-income countries.
With that in mind, a just-published study looking at trends in England and Wales has rung an alarm bell that the trend could be at risk of going in the other direction, and leave healthcare systems unprepared for unexpectedly high case numbers in the future.
The paper published in The Lancet Public Health has looked at the dementia incidence trend between 2002 and 2019 using data in adults aged 50 years and older from the English Longitudinal Study of Ageing and attempted to project the burden of the disease in 2040.
It found a 29% decline from 2002 to 2008 which was however almost cancelled out by a 25% increase between 2008 and 2016. The pattern was observed across subgroups according to age, sex, and educational attainment.
Although an increase in dementia cases has often been attributed to an ageing population, the researchers also found that the rate of dementia onset within older age groups is also increasing.
If the current trend continues at the same rate – factoring in the general ageing of the population – there will be 1·7 million dementia cases in England and Wales by 2040, approximately twice the number in 2023 and 42% more than previously forecast, according to the authors, led by Dr Yuntao Chen of the UCL Institute of Epidemiology and Health Care in London.
“Not only will this have a devastating effect on the lives of those involved but it will also put a considerably larger burden on health and social care than current forecasts predict,” said Chen. “Continued monitoring of the incidence trend will be crucial in shaping social care policy.”
Among the intriguing findings in the data was both a slower decline in 2002-2008 and a faster increase after 2008 in subjects with lower educational attainment, which the researchers suggest may result from socio-economic inequalities in dementia risk factors like midlife obesity.
Principal investigator Prof Eric Brunner, also of UCL, said: “We don’t know how long this pattern will continue but the UK needs to be prepared so we can ensure that everyone affected, whatever their financial circumstances, is able to access the help and support that they need.”
Commenting on the results, dementia specialist Prof Tom Dening of the University of Nottingham said the figures may not be too surprising as life expectancy has stopped increasing in recent years, and there has been an increase in various long-term conditions that are risk factors for dementia.
“The figures also reflect other evidence, not just from health research, that the gap between the wealthy and the poorest in our society has increased in the last decade or more,” he added.
“Some people might point to the UK political climate as significant in this regard. It would be interesting to see if the trends reported in this paper are mirrored in other countries with less polarised distribution of wealth and resources.”
Not all scientists agree with the interpretation, however. Prof David Curtis, an honorary professor at the UCL Genetics Institute, who was not involved in the study, said the assumption in the analysis that rates will rise by 2.8% every year may not be accurate as the estimated incidence of dementia “tends to jump around quite a bit.”
“We’ve already seen that incidence does not follow a linear trend,” he argued. “From a medical point of view I don’t see why cases should just continue to go up and up at the same rate year on year. It is true that dementia is a huge public health problem with terrible consequences but I do not think this study can tell us much about how many cases we may be seeing in 2040.”
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