ArticlesDifferences in risk factors, atherosclerosis, and cardiovascular disease between ethnic groups in Canada: the Study of Health Assessment and Risk in Ethnic groups (SHARE)
Introduction
Ethnicity-based research can identify new clues to pathogenesis of a disease, since the populations under study are heterogeneous in genetic and lifestyle characteristics. There is increasing evidence that rates of cardiovascular disease vary between ethnic groups. Previous studies indicate that people of South Asian origin have higher rates of this disease than people of European origin, a finding that cannot be explained by differences in conventional cardiovascular risk factors, such as smoking, raised blood pressure, diabetes, or high cholesterol.1, 2 Conversely, people of Chinese origin have lower rates of cardiovascular disease than people of European origin, and with the exception of glucose intolerance, have a more favourable risk factor profile.3, 4
These findings were confirmed by a recent analysis of Canadian mortality data, in which South Asian Canadians had the highest rates of cardiovascular disease, Canadians of European origin had intermediate rates, and Chinese Canadians had the lowest rates.5 To examine this variation we measured the prevalence of cardiovascular disease in Canadians of South Asian, Chinese, and European origin and then identified whether these differences could be explained by: conventional risk factors; novel risk factors (fibrinogen, plasminogen activator inhibitor-1 [PAI-1], lipoprotein (a), homocysteine); or atherosclerosis as measured by B-mode carotid ultrasonography.
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Study population
The Study of Health Assessment and Risk in Ethnic groups (SHARE) is a prospective investigation of atherosclerosis, cardiovascular disease, and its determinants in three ethnic groups in Canada: South Asians, Chinese, and Europeans.6 Canadians were classified as South Asian if their ancestors originated from India, Pakistan, Sri Lanka, or Bangladesh; Chinese if their ancestors originated from China, Taiwan, or Hong Kong; and European if their ancestors originated from Europe. Participants were
Ultrasonography
Subclinical atherosclerosis was measured in all participants by carotid B-mode ultrasonography. In Hamilton and Toronto, a high resolution ACUSON/ACOUSTIC RESPONSE TECHNOLOGY ART 1 imaging system (Mountain View, CA, USA), equipped with a 7·5 MHz broad bandwidth frequency carotid probe was used. In Edmonton, the ATL-UM9-HDI (Bothell, WA, USA) imaging system equipped with a 10 MHz transducer was used. All ultrasound examinations were recorded on S-VHS tapes and subsequently digitised and analysed
Participants
Of the 7728 households selected in the initial random sample, 5769 (75%) were contacted, 3172 (55%) of these completed the screening telephone call, and 1566 (49%) were eligible. Of this group, 985 (63%) individuals completed all components of the clinic visit. The response rate among eligible individuals did not vary much between ethnic groups: 342 of 579 (59%) South Asians responded, 317 of 458 (69%) Chinese, and 326 of 529 (62%) Europeans. When data from non-responders (n=1527) were compared
Discussion
We have confirmed the national mortality patterns that Canadians of South Asian origin have an increased prevalence of cardiovascular disease compared with Canadians of European and Chinese origin.5 We reported that carotid atherosclerosis was higher in participants with prevalent disease across all ethnic groups, supporting its validity as a surrogate marker for disease. However, the much lower amount of carotid atherosclerosis seen among South Asians, even after adjustment for age, sex, and
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