Researchers of brain ageing from around the world come together in the COSMIC collaboration to determine what factors are common for cognitive decline and dementia in all human populations irrespective of race, ethnicity and socioeconomic development.
Ageing is intricately connected with cognitive decline, and there is an increasing proportion of life lived with cognitive impairment as age increases. If an impact is to be made on this disability burden, we must understand the risk and protective factors for cognitive decline, frailty and chronic disease associated with ageing. The best approach is to study this using population-based ageing cohorts. A large number of such studies are ongoing internationally, and have identified a diverse range of factors . There is considerable inconsistency in the results produced . The existing evidence therefore needs further systematic examination. This also relates to the evidence for vascular risk factors as risk factors for Alzheimer’s Disease (AD). While many publications have previously argued for this, a recent review concluded that “at the present time, there is no consistent body of evidence to show that vascular risk factors increase AD pathology” .
We argue that the way to deal with these inconsistencies is to try to harmonise the international studies so that data can be pooled and risk factors examined with greatly increased power. There have been a number of attempts to do this recently, but the scope of these attempts has been limited. The HALCyon (Healthy Ageing across the Life Course) is a consortium of 9 UK-based cohorts of individuals older than 50 that have biosocial assessments. However, their assessments are mostly at two time points (child or adulthood and old age), and these are not longitudinal cohorts of ageing individuals with repeated measurements and dementia or decline as end-points. CHANCES (Consortium on Health and Ageing: Network of Cohorts in Europe and the United States) includes 14 cohorts, covering populations from 18 EU Member States, four associate countries, and three additional countries. The objectives are broad, with the key areas being cancer and cardiovascular disease. Two other consortia have been developed for ageing-related research, with the focus being on genomic epidemiology - CHARGE (Cohorts for Heart and Aging Research in Genomic Epidemiology) and ENIGMA (Enhancing NeuroImaging Genetics through Meta-Analysis).
COSMIC (Cohort Studies of Memory in an International Consortium) is a recently established endeavour that aims to bring together cohort studies of cognitive ageing internationally in order to facilitate a better understanding of the determinants of cognitive ageing and neurocognitive disorders. The two main objectives of this project are to:
1. Harmonise shared, non-identifiable data from cohort studies that longitudinally examine change in cognitive function and the development of dementia in older individuals (60+ years).
2. Perform joint or mega-analyses using combined, harmonised data sets that yield collated results with enhanced statistical power, in addition to comparisons across geographical regions.