Cognitive decline across different countries – COSMIC

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by Darren Lipnicki

The Cohort Studies of Memory in an International Consortium (COSMIC) is a collaborative effort of researchers from around the world. We identify important topics for research, and share data from longitudinal, population-based studies of cognitive ageing to create a better understanding of what causes dementia, including Alzheimer’s disease.

Our current project is investigating whether there are differences between countries in how fast cognitive functioning declines in older individuals. Such differences could help explain why the prevalence of dementia varies around the world. The highest rates of dementia are reported from Latin America and the lowest from sub-Saharan Africa, with all other regions, including Australia, somewhere in-between.

For this project we obtained data from 14 different studies, representing 12 countries from North and South America, Europe, Asia, and Australia. The total sample size is large, with over 42,000 individuals. We are investigating how cognition changes with age using the Mini-Mental State Examination (a screening tool for dementia), and other, more-specific tests of cognitive functioning that include memory, speed of information processing, language and executive functioning.

We are also examining whether changes in cognition are associated with being male or female, and how many years of education a person has. This is important because dementia is generally more prevalent among women than men, and education may help to protect against or delay dementia. However, educational opportunities vary widely around the world, and are not always equal for males and females. Another factor we are examining in this project is a known genetic risk factor for Alzheimer’s disease (being an apolipoprotein E ε4 allele carrier). 

Preliminary results show that all cognitive measures decline with age, and the rate of decline increases at advanced age.  However, this rate is not the same in all countries and ethnic groups. Higher levels of education slowed the rate of decline on the MMSE, suggesting that higher education could protect against or delay the onset of dementia.The full details of this analysis are being peer-reviewed for publication. 

Knowing whether cognition declines at faster or slower rates in different countries will help to clarify why the prevalence of dementia varies around the world. Because our project has such a large and globally representative sample, the results should also provide a more accurate account of how cognitive decline is affected by factors like sex and education. In future research, we will investigate how cardiovascular, lifestyle and other important risk factors are also involved. Understanding the causes of Alzheimer’s disease and other dementias is necessary to develop interventions and policies that will work to minimise the individual and global impact of these conditions.

 

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