CADI in Canada ─ Lessons for the Indian Diasporas
- The 1.3 million South Asians in Canada account for 4% of its population and have surpassed Chinese as the largest minority.1
- The rates of CVD (cardiovascular diseases) and cancer vary markedly among various ethnic groups in Canada. White Canadians have high death rates from both cancer and CAD (coronary artery disease or heart disease), whereas Canadians of Indian descent have high death rates from heart disease and lower death rates from cancer. Chinese Canadians, by contrast, have low death rates from heart disease but high death rates from cancer.2
- The Canadian government has encouraged studies of CAD among South Asians, since the cost of the excess burden of heart disease is born by the government. Earlier studies showed that South Asians have 45% to 50% higher risk of deaths from heart attacks and heart disease, whereas Chinese have a 35% lower risk compared to Europids.2,3, 4
- The prevalence of heart disease was 11% in the SHARE Study, very similar to the 10% from the CADI Study in the US.5 6 The prevalence of CAD among South Asians was double that of Europids (5%) and five times higher than for Chinese (2%).5
- Besides, for the same degree of atherosclerosis (plaque buildup), the CAD rates were double for South Asians but only half for Chinese compared to Europids.5 When compared with other Canadian populations, South Asians are more likely to have evidence of silent heart disease.5
- Several studies have repeatedly demonstrated the three cardinal features of heart disease among South Asians in Canada ─ prematurity, severity, and a genetic predisposition mediated by elevated lipoprotein(a) blood levels.
- South Asians develop heart attack at a young age; 49% of heart attack occurs in South Asians younger than 65 years of age compared to 31% in Chinese and 37% among whites.7 South Asians present to hospital later, with more anterior or large heart attack which is associated with greater complications and adverse outcomes.8
- Following a heart attack, South Asians have 50% higher chance of having a bypass surgery and yet one-year death rate is 3 times higher─ both indicative of malignant heart disease in this population.9
- South Asians undergoing coronary angiography have a 2-fold higher rate of left main (the most severe form of heart disease) and triple-vessel disease compared with white patients, a difference that was more pronounced in women.10
- South Asian patients undergoing coronary bypass surgery in Canada are younger but had more severe and triple-vessel disease and double the mortality compared to whites.10 South Asians also had greater post operative complications such as heart attack, low output syndrome, and sternal wound infections resulting in poor outcome and survival than Europids.10, 11 South Asian kidney-transplant patients have high post surgery CVD risk (3-fold).12
- Compared to European- and Chinese-born Canadians, South Asians had similar or lower rates of tobacco use, treated high blood pressure, and treated hyperlipidemia.3-5 South Asians’ risk of diabetes is more than three times that of immigrants from Western Europe and North America.13 Several studies in Canada and elsewhere have shown that South Asians are more likely to be sedentary.3-5
- A recent study of Ontario population showed the highest prevalence of heart disease and stroke among South Asians─higher than whites and all other ethnic groups. The differences in the prevalence of CAD, stroke, and major modifiable risk factors are given in the Table 107A.14
Table 107 A. Prevalence of CVD Risk Factors and CVD by Ethnicity in Ontario Canada14
|Inadequate fruits and vegetables % **||22.1||22.1||19.2||24||24.4|
|Inadequate physical activity%***||63.9||62.7||72.8||72.8||68.3|
|Non-regular alcohol consumption %||68.5||65.5||89.0||91.2||85.3|
|Heart disease %||5.0||5.1||5.2||3.2||3.4|
|Heart disease or stroke %||5.7||5.7||6.6||3.8||4.4|
|* Body mass index more than 30; ** less than 3 per day; *** less than 15 minutes per day|
- South Asians had low rates of smoking (9%) and obesity (8%), higher prevalence of diabetes (8%) and high blood pressure (17%) but the highest rates of physical inactivity (73%) and the highest prevalence of heart disease (5.2%) and stroke (1.7%) whereas Chinese had the lowest prevalence of risk factors, heart disease, and stroke compared to whites.
- Blacks had high prevalence of risk factors including diabetes, high blood pressure, and obesity but low rates of heart disease.14 However, the risk factor profile does not explain the excess burden of CVD among South Asians.
- In sharp contrast to the traditional risk factors, Asian Indians have a disproportionately higher burden of abdominal visceral fat, microalbuminuria, dyslipidemia, higher lipid ratios (apo B/ apoA1 and T/C HDL ratio) and prothrombotic factors such as high homocysteine and high lipoprotein(a).3-5 5, 15
Decline in CAD mortality
- Since 1970, the age-adjusted CAD mortality has declined substantially in Canada ─ 70% for men and 41% for women.16 Although, the decline was initially slower in South Asians, the decline has now accelerated.
- Between 1994 and 2005, the age-adjusted CAD mortality rate in Ontario decreased by 35%.17 Improvements in medical and surgical treatments were associated with 43% and trends in risk factors accounted for 48% of this decrease. Specifically, reductions in total cholesterol contributed to 23% and systolic blood pressure 20%.
- However, increasing diabetes prevalence and body mass index had an inverse relationship associated with higher CAD mortality of 6%.17 Improvements in patients with chronic stable heart disease contributed to 17%, heart failure 10%, and heart attacks 8%.17
- Recent data show that heart disease rates among South Asians have decreased to that of whites, probably due to greater awareness of the excess risk and universal access to health care that precludes catastrophic health care spending.4, 7, 18 This Canadian experience clearly demonstrates that the death toll from heart disease among South Asians can be reduced by effective interventions.
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