Covert Vascular Brain Injury and Cognitive Dysfunction Among Chinese Adults Living in Canada and China: The CAHHM and PURE-MIND Studies.

Background and objective: It is unclear whether variation in covert cerebrovascular disease prevalence is attributable to ethnic differences or to other factors. We aimed to examine the associations of country of residence with covert vascular brain injury (VBI) and cognitive dysfunction among Chinese adults residing in Canada and China.

Methods: This was a multisite cross-sectional study of Chinese adults aged 40-80 years in the Canadian Alliance for Healthy Hearts and Healthy Minds (CAHHM; January 1, 2014, to December 31, 2018) and Prospective Urban Rural Epidemiological-Mind (PURE-MIND; November 1, 2010, to July 31, 2015) cohorts living in Canada and China. The exposure was country of residence. The co-primary outcomes were covert VBI (defined as MRI findings of high white matter hyperintensities or covert brain infarct) and cognitive dysfunction (defined as a Montreal Cognitive Assessment [MoCA] score <26). We used generalized linear models to describe the association between country of residence and each outcome, adjusting for selected covariates.

Results: We included 884 adults living in Canada (mean age 57.3 years, 55.4% female) and 473 living in China (mean age 56.8 years, 60.3% female). Participants in Canada had a lower prevalence of covert VBI (age 65-79 years: male, 11.5%; female, 12.2%) than those living in China (age 65-79 years: male, 62.9%; female, 52.1%). Prevalence of MoCA score <26 was lower among men and women in Canada (age 65-79 years: 40.2% and 30.0%, respectively) than among men and women in China (age 65-79 years: 74.3% and 79.2%). Living in China was associated with a 6-fold increase in the odds of covert VBI (5.85, 4.06-8.45), which remained significant after covariate adjustment. Living in China was associated with a 7-fold increase in the odds of MoCA score <26 (6.98, 5.38-9.04), which was no longer significant after covariate adjustment.

Discussion: Despite sharing a similar ethnicity, the prevalence of covert VBI and cognitive dysfunction varied substantially by country of residence. Disparities in cognitive dysfunction were completely explained by differences in education and traditional cerebrovascular risk factors, whereas disparities in covert VBI prevalence were only partially explained by differences in such factors, suggesting a role for other environmental factors.