Stroke risk is primarily linked to differences in traditional stroke risk factors, like diabetes and high blood pressure, rather than ethnicity, according to findings from a new South London study conducted at King’s College London.
The research found that while Asian and Black individuals were more likely to have diabetes or hypertension than White individuals, the likelihood of someone having a stroke once they had these conditions was similar across ethnic groups.
Although previous research has consistently shown higher rates of stroke in some ethnic groups and has identified hypertension and diabetes as important contributors to these inequalities, the role of ethnicity on the risk of stroke has remained controversial.
The King’s College London study – funded by King’s Health Partners , Guy's & St Thomas's Charity and the National Institute for Health and Care Research (NIHR) – set out to examine this relationship in more detail by looking separately at the development of cardiometabolic risk factors and the subsequent progression from these conditions to stroke.
Published in BMC Public Health , the study analysed primary care electronic records from more than 650,000 people in South London, collected from 41 GP practices in Lambeth between 2005 and 2021. The study included patients of Asian, Black and White ethnicity and examined three major risk factors for stroke: hypertension (high blood pressure), diabetes and hypercholesterolaemia (high levels of cholesterol in the blood).
To study the relationship between ethnicity, the cardiometabolic risk factors and stroke, the researchers used a modelling technique called a ‘multistate analysis.’
This technique allows researchers to analyse how an individual moves through different health events or ‘states’ over time – in this case moving from having no risk factors, to having one of the risk factors, and then on to having a stroke. Using this method, the researchers calculated the probability of individuals moving from one state to the next.
As the researchers expected, the occurrence of stroke risk factors was higher in Black and Asian patients than in White patients. Ethnicity was significantly associated with the probability of developing all three stroke risk factors, especially diabetes and hypertension. Compared with White patients, Black patients were around twice as likely to develop hypertension and more than twice as likely to develop diabetes. Asian patients were about 50% more likely to get hypertension and were three times as likely to get diabetes than White patients.
However, when the researchers looked at the transition from stroke risk factor to stroke itself, these patterns disappeared. Among patients with hypertension or diabetes, Black and Asian ethnicity did not confer a higher probability of progressing to stroke than that observed in White patients with the same conditions. The authors say this finding confirms that ethnic inequalities in stroke incidence are primarily associated with the cardiometabolic risk factors.
Dr Marc Delord, Research Fellow in Medical Statistics at King’s College London, said: “We know that stroke occurs more frequently in some ethnic groups. Our study explains that these inequalities are attributable to traditional modifiable cardio-metabolic risk factors only: Although Black and Asian patients were more likely to develop these risk factors, particularly hypertension and diabetes, once these conditions are present, their subsequent probability of stroke was not higher than that of White patients.
“Our findings reinforce the need for prevention, detection and management strategies that account for the higher burden of these modifiable risk factors observed in Black and Asian populations, including culturally tailored lifestyle interventions, to help reduce inequalities in stroke risk.”
Professor Abdel Douiri, Professor of Medical Statistics and Clinical Trials at King’s College London and co-author of the paper, added: “These findings underscore a clear message: reducing ethnic disparities in stroke requires addressing the underlying inequalities in the prevention, early detection, and effective management of hypertension and diabetes, which disproportionately affect Black and Asian communities.”
Hypercholesterolaemia did not fit the same pattern as the other risk factors. Among Black patients with hypercholesterolaemia, the study identified a slight increase in the subsequent likelihood of stroke compared with White patients. The authors say this finding needs further investigation.
Previous research recently published in BMC Medicine from the team in the same study population found that Black patients with hypercholesterolaemia were less likely to receive statin treatment. Although data on medication prescribing were not included in the current study, the researchers would like to investigate whether the reduced prescribing of statins could help to explain the increased occurrence of stroke observed in this population.
BMC Public Health