How is the prevalence and incidence of dementia changing over time? A new Cambridge study, just published in Nature Reviews Neurology, suggests we are experiencing stable or declining prevalence and incidence of dementia. It also indicates evidence of sex-specific differences in these changes to dementia occurrence.
We are living in a time where population ageing is unprecedented, and the twenty-first century will witness even more rapid ageing than the century just past. As a consequence, age related conditions, such as dementia, are an important public health issue and an increasing focus for policymakers, civil organizations and researchers.
Currently dementia research is focused on neurological features, pathophysiological mechanisms and drug discovery. However, this approach cannot provide an understanding of the full spectrum of dementia in the general population, or identify risk factors across different populations and life courses.
For this study a team of researchers, led by Professor Carol Brayne at the University of Cambridge’s Institute of Public Health, brought together the worldwide evidence on dementia in older populations to gain insights into how the prevalence and incidence of this condition is changing over time, and whether known protective and risk factors can explain these changes.
For this narrative review, they synthesized the findings from those few international studies that investigated changes in dementia prevalence and incidence in comparable populations over time.
To establish whether trends are emerging, the team compared population-based studies that used similar diagnostic and research methods to investigate dementia prevalence (nine studies) and incidence (five studies) at different time points. The studies were from Sweden, Spain, the UK, the Netherlands, France, the USA, Japan and Nigeria. Besides the Japanese study, they all indicated stable or declining prevalence and incidence of dementia age for age, and some provided evidence of sex-specific changes.
What explains these findings? Carol Brayne, lead author of the study says: “No single risk or protective factor has been identified that fully explains the trends, but major societal changes and improvements in living conditions, education and healthcare could have influenced individuals’ physical, mental and cognitive health throughout their life to reduce their risk of developing dementia.”
She goes on to emphasise the importance of conducting further research to better inform future public health planning and policy:
“Further research to identify the factors that contribute to reductions in prevalence and incidence of dementia in particular countries and regions should become a major priority, as these findings could have important implications on health and social policies in relation to dementia prevention and risk reduction. Analytical epidemiological approaches combined with translational neuroscientific research could provide a unique opportunity to further explore this.”
Yu-Tzu Wu, Alexa S. Beiser, Monique M. B. Breteler, Laura Fratiglioni, Catherine Helmer, Hugh C. Hendrie, Hiroyuki Honda, M. Arfan Ikram, Kenneth M. Langa, Antonio Lobo, Fiona E. Matthews, Tomoyuki Ohara, Karine Pérès, Chengxuan Qiu, Sudha Seshadri, Britt-Marie Sjölund, Ingmar Skoog & Carol Brayne. The changing prevalence and incidence of dementia over time — current evidence. Nature Reviews Neurology; 12 May 2017; DOI: 10.1038/nrneurol.2017.63
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