‘Healthy immigrant effect’ may explain lower rates of stroke, TIA

Immigrants to Canada had lower rates of stroke or transient ischemic attack compared with long-term residents, with rates varying by age, stroke type and country of origin, according to results of a province-wide retrospective analysis.

“Immigrants tend to have better health than long-term residents due to the presence of a healthy immigrant effect whereby those who are healthy are more likely to immigrate,” Manav V. Vyas, MBBS, of the division of neurology in the department of medicine at the University of Toronto, and colleagues wrote in Neurology. “A lower incidence of cancer, psychotic disorders and myocardial infarction has been found in immigrants compared [with] long-term residents. However, it is unclear if the incidence of stroke, a leading cause of disability, is also lower in immigrants.”

The researchers aimed to assess the link between immigration status and stroke incidence among 8 million adults, of whom 15% were immigrants, who resided in Ontario, Canada, on Jan. 1, 2003, and who had no history or prior stroke or TIA. Follow-up lasted until March 31, 2018, with the aim of identifying stroke or TIA, which the researchers defined as hospitalization or ER visit. They used cause-specific hazard models that adjusted for demographics and comorbidities to estimate adjusted HRs of stroke or TIA among immigrants compared with long-term residents. Further, they assessed whether variations in age, stroke type or country of origin of immigrants impacted the association.

Data analysis included 109 million person-years of follow-up and 235,336 observed incident stroke or TIA events. Results showed immigrants had a rate of stroke or TIA of 10.9 per 10,000 person-years compared with 23.4 per 10,000 person-years among long-term residents (HR = 0.66-0.68). The difference in rates persisted across all age groups and stroke types. The HR among immigrants compared with long-term residents was 0.71 for ischemic stroke, 0.89 for intracerebral hemorrhage, 0.85 for subarachnoid hemorrhage and 0.53 for TIA.

Immigrants from the Caribbean (HR = 0.95; 95% CI, 0.91-1), Latin America (HR = 0.85; 95% CI, 0.82-0.91) and Africa (HR = 0.8; 95% CI, 0.74-0.85) had a less pronounced magnitude of the reduction in stroke risk linked to immigration status compared with those from other world regions.

“The overall lower risk [for] stroke or TIA in immigrants should prompt future studies to understand the mediators of this healthy immigrant effect and use this knowledge to develop targeted primary preventive measures to reduce the risk [for] stroke in both immigrants and long-term residents,” Vyas and colleagues wrote.