In this large population-based study in Ontario, we found striking differences across ethnic groups in the prevalence of cardiovascular risk factors and diseases. The white population had a disproportionately higher prevalence of smoking and obesity, whereas the South Asian and black populations had disproportionately higher prevalences of diabetes and hypertension. People of Chinese origin had significantly lower levels of most cardiovascular risk factors, heart disease and stroke, whereas those of South Asian origin had intermediate levels of risk factors and the highest prevalence of heart disease and stroke. A paradox was observed in the black population, whereby high levels of cardiovascular risk factors were accompanied by a relatively low prevalence of heart disease. A key finding from this study was that the white, South Asian, Chinese and black populations in Ontario had distinct cardiovascular risk profiles, which suggests the need for the development of ethnic-specific cardiovascular risk prevention programs and health services in Canada.
The overall prevalence of heart disease and stroke was highest among South Asian respondents and lowest among Chinese respondents. This is consistent with results from the Study of Health Assessment and Risk in Ethnic groups living in three Ontario cities, which found a disproportionately higher prevalence of cardiovascular disease among South Asian participants (10.7%) than among Chinese participants (2.4%).3
Our study findings are also consistent with a previous study of 1.2 million deaths in Canada, which showed that the rates of cardiovascular-related mortality were highest in the South Asian population, followed by the European and Chinese populations.17
The high risk of heart disease that we observed for the South Asian respondents might be explained in part by their relatively high susceptibility to insulin resistance and the metabolic syndrome, which is characterized by central obesity, glucose intolerance, a poor lipid profile and diabetes.18–20
In our study, South Asian respondents were 1.91 times more likely to have diabetes than white respondents, a result similar to that reported in a previous investigation of biochemically measured diabetes.3
A noteworthy observation in our study was the much lower levels of smoking observed among Chinese (8.7%) and South Asian (8.6%) respondents living in Ontario relative to rates documented in China (28.9%)21
and India (15.6%).22
These findings might be attributable in part to a “healthy immigrant” effect and/or Canada’s tougher antismoking policies. In Ontario, physical inactivity was most prevalent among Chinese and South Asian respondents. Although people of these ethnic backgrounds have a lower average body mass index than white people, there is growing evidence that they also tend to have a higher percentage of body fat and a greater risk of cardiovascular events at a lower body mass index.23,24
As such, regular exercise and maintenance of a healthy weight are important goals for South Asian and Chinese people.
Despite a higher prevalence of most traditional cardiovascular risk factors, the black population had a lower prevalence of heart disease than the overall population. This paradox might be explained, at least in part, by the lower levels of smoking and psychosocial stress reported by this group. Populations of African descent also have lower levels of plasma fibrinogen than the general population, which would decrease their risk of thrombosis and clinical events.25,26
The relatively low prevalence of heart disease among black respondents might also be a function of differential survival rates for this group relative to the other ethnic groups. For example, studies in the United States have reported that black people undergo fewer invasive cardiac procedures and tend to have poorer survival rates after myocardial infarction than white people,27–29
which could lead to a survival bias and apparent paradox of lower prevalence of heart disease if black patients die relatively soon after developing heart disease.
The cross-sectional design of this study limited our ability to draw conclusions about the causal relationships between risk factors and disease. Another limitation of the study was that our analyses were based on data, including ethnicity, that were self-reported rather than measured. There is no “gold standard” for defining ethnicity, and self-reported ethnicity is the best measure currently available. We were also unable to analyze variables that were not routinely collected in the surveys (e.g., information about lipids, waist-to-hip ratio and family history of cardiovascular diseases). Nevertheless, these limitations were counterbalanced by the much larger sample size that was possible in this study as compared with most previous studies involving direct physical measurements. Furthermore, the findings presented here are congruent with those based on direct measurements and are generally consistent with those of earlier comparisons of two or three ethnic groups. We recognize that diversity also exists within each of the four ethnic groups and that the ethnic differences presented in this study are the results of complex interactions between and among genetics, lifestyle, socio-economic status, provision of health care and reporting. Further examination of these interactions is necessary.
Despite universal access to health care, ethnic groups living in Ontario differed markedly in their cardiovascular risk profiles. Awareness of these differences will become increasingly important as ethnic minority groups come to represent a larger proportion of the Canadian population. Although Canada is one of the most ethnically diverse countries in the world, relatively little research has been done on ethnic differences in cardiovascular health, and most cardiovascular prevention programs and policies are targeted to the general population and have been based on studies typically involving the white population. Our findings suggest that there may be a need to develop ethnically tailored strategies for preventing cardiovascular risk factors in Canada. Developing strategies for preventing diabetes and hypertension that are targeted specifically to high-risk South Asian and black populations, designing obesity-prevention programs for black women and for white people, and promoting physical activity among South Asian and Chinese people and black women are some examples of approaches that might help to reduce ethnic disparities in cardiovascular risk factors and the burden of cardiovascular disease.