Cardiovascular disease (CVD) is the major cause of death in Canada and most developed countries. One of the next major advances in reducing CVD morbidity and mortality will likely occur when the epidemiology and the pathophysiology of specific risk factors for atherosclerosis across diverse populations are better understood. It is now apparent that different ethnic groups have different risks of CVD mortality that cannot be accounted for by differences in risk factors like smoking, hypertension, hypercholesterolemia, and diabetes. Therefore, both from global and national perspectives, studies that explore reasons for ethnic differences in CVD rates are of major public health importance. The Study of Heart Assessment and Risk in Ethnic groups (SHARE) is a unique initiative designed to determine the prevalence of subclinical atherosclerosis and cardiovascular risk factors in South Asians and European Canadians. South Asians in Canada and in several countries have the highest rates of coronary heart disease (CHD) compared to any other ethnic groups in the world, and present a unique opportunity to test research hypotheses to discover emerging risk factors for atherosclerosis. SHARE builds upon previous cross-sectional studies that have examined the traditional CHD risk factor profile of South Asians, and extends this investigation to determine the prevalence of subclinical atherosclerosis in South Asians, and the contribution to its development from metabolic, fibrinolytic, nutritional, and psychosocial factors. This thesis represents a carefully designed research proposal to study CVD risk factors and subclinical atherosclerosis in South Asians and White Canadians. A pilot study to test the feasibility of this design was conducted over the past one year. The information obtained from this experience has led to further pilot studies and modification of the final proposal, which has recently been funded by the Medical Research Council of Canada. This cross-sectional study proses to use a stratified random sampling to identify potential South Asian and White Canadian participants in Canada. Ethnic specific sampling frames were created, in conjunction with Statistics Canada, by using a compact disc programme of public telephone directories. South Asian Canadians were identified by using a comprehensive list of last names, a method which is highly sensitive and specific to South Asian ethnicity. A sampling frame of Canadians of European origin matched by postal code to the South Asian sampling frame was also created. In the pilot study we recruited participants by mail and multiple telephone calls, and our results are comparable to other population-based studies who utilized similar methods of recruitment. However, it is likely that our contact rates may be improved and after seeking the advice of the York Institute for Social Research in Toronto we have modified our recruitment protocol to maximize contact rates. Both traditional and emerging risk factors will be identified utilizing a combination of existing and new measurement instruments. The primary outcome measurement is subclinical atherosclerosis as measured by the carotid B-Mode ultrasound. This technology allows precise quantitation of atherosclerosis and is desirable for use in population-based studies as it is not subject to reporting bias by study participants. As well, it is a continuous measurement and decreases sample size requirements. Furthermore it allows the study of the relationship of risk factors and disease across a continuum. Interesting demographic and laboratory differences were identified between the South Asians and White Canadian populations during the pilot study. Lifestyle differences in smoking and alcohol consumption, as well as socio-economic status and education were identified between the groups. As well, intriguing differences in glucose and lipid abnormalities were identified, as were differences in emerging CVD risk factors such as Lp(a) and urine microalbumin. Although extensive measures of fibrinolysis were not incorporated into the pilot study they are planned for the large study.
Few instruments to measure nutritional and psychosocial factors in nonwhite populations have been developed. The development of these instruments is outlined in this thesis proposal and. preliminary validation of these instruments has been completed as part of the SHARE pilot study. In both of these areas no “gold standard” exists against which surrogate measures may be validated and this posed unique methodologic challenges. After careful consideration of nutritional hypothesis and discussion with experts in the field of nutritional epidemiology, it was decided that a food frequency questionnaire (FFQ) would be the most appropriate instrument to identify significant qualitative differences in macronutrient consumption between ethnic populations. As no FFQ exists for South Asians, nutrient data collected from the SHARE pilot study were used to create a South Asian specific FFQ. With the initiation of the large SHARE project this FFQ will be validated against multiple 24 hour recalls taken at random. Although psychosocial factors have been repeatedly demonstrated to be associated with the development of CVD, it is extremely difficult to study these relationships precisely. There are many instruments which have be validated to measure stress and associated factors such as hostility, coping strategies and depression, yet no validation of these instruments had been conducted in the South Asian population. Therefore a SHARE Life Stress and Satisfaction Questionnaire was created after careful consideration of which stress factors may be unique to South Asians immigrants. Previously validated subscales were compiled to create this questionnaire which was completed by a subset of the SHARE pilot study participants. Validation of this questionnaire was performed on three levels content, criterion and construct. As well, reliability testing using tests of internal consistency and test-re-test reliability were conducted. Although this satisfies the criteria of validation and reliability testing of psychosocial instruments, whether or not we were attempting to measure the relevant stress factors of South Asian Canadians is questionable. In our attempt to confirm what we believed were important stressors, and to discover new factors, a qualitative substudy was designed. Using focus groups a subsample of South Asian and White Canadians will be studied and the emergent themes generated from this study will be used to develop an explanatory model of the dominant psychosocial factors and their potential relationship with health behaviours and disease status. This substudy will be run concurrently with the initiation of the SHARE project, and based on these results the Life Stress and Satisfaction questionnaire will be modified. In summary, this thesis outlines a proposal to document the prevalence of traditional and emerging risk factors and sub-clinical atherosclerosis in South Asians and White Canadians in Canada. It is our intention to follow the group identified in this cross-sectional study (Phase 1) for the progression of atherosclerosis and clinical events over time in a national cohort study (Phase 2). / Thesis / Master of Science (MS)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/25305 |
| Date | January 1996 |
| Creators | Anand, Sonia |
| Contributors | Yusuf, Salim, Clinical Epidemiology/Clinical Epidemiology & Biostatistics |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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