Background: It is widely known that South Asian and Black minority ethnic groups, in the United Kingdom, have a higher incidence and prevalence of cardiovascular disease and it is thought that this may in turn place these ethnic groups at a greater risk of developing dementia than the White ethnic groups. This study seeks to explore this theory further, using large scale population-based databases, in the United Kingdom.
Methods: All eligible participants over the age of 50 years from the CPRD database, that were free from a diagnosis of dementia at time of entry to the study, those with an ethnic coding were stratified into 5 different ethnic groups, White, Black, South Asian, East Asian and Mixed. Their trajectories were followed over the observation period from 1996 to the end of the study (2016). Cardiovascular Disease (CVD) and available lifestyle risk factor data relating to the development of dementia were also recorded over this period.

Results: A total of 1,091,242 individuals were included in the analytical sample, after exclusion of those with missing ethnicity data. There were a total of 174,546 (16.3%) cases of ascertained dementia. The white ethnic group had a higher mean age of dementia onset 81.8 years (SD 8.6) just ahead of the East Asian 80.3 years (8.9) ethnic group and the lowest mean age of onset seen in the Black ethnic group 76.3 years (SD 9.4). The fully adjusted Cox regression model (adjusting for all covariates including, socioeconomic status and education) revealed a lower risk of incident dementia in the Black [HR 0.83 (95% CI 0.74-0.93)] and South Asian ethnic groups [HR 0.55 (95% CI 0.49-0.61)], and the excessive risk in East Asian ethnic group was no longer found to be significant [HR 1.14 (95% CI 0.93-1.42)]. The East Asian ethnic group had a higher cumulative incidence of dementia than any other ethnic group when accounting for death as a competing risk [sdHR 1.37, (95% CI 1.18-1.58 for East Asian compared to White ethnicity]. However, overall cumulative incidence rates of dementia did not significantly change between the other ethnic groups when accounting for death as a competing risk.

Conclusion: The lower incidence of dementia seen in the Black and South Asian groups is intriguing and may be due to case under ascertainment amongst these ethnic groups, in view of their higher risk of cardiovascular disease. Understanding the differences for ethnic variation in dementia rates is not only vital for aetiological research but also for the development of prevention strategies, health service planning and resource allocation.