Cardiovascular disease in East Asian immigrants living in Australia: considerations in relation to vitamin D deficiency, smoking and acculturation
Creators: name: Guo, Shuyu
Publisher: name: The Australian National University
Year: 2016
Subjects: Cardiovascular disease
East Asian immigrants
vitamin D deficiency
smoking
acculturation

description: BACKGROUND: Cardiovascular disease (CVD) is the leading cause of death in Australia and accounts for the second highest disease burden in disability-adjusted life years. Meanwhile, according to a recent report 28.1% of the estimated resident population of Australia was born overseas; this is the highest proportion of immigrants in the past 120 years. Patterns of CVD risk, incidence, and mortality vary significantly across different ethnic population groups. This means that the demographic change in the Australian population due to overseas immigration is likely to alter patterns of CVD in terms of incidence, prevalence, and mortality in both the short and long term. These changes may challenge existing health policies, models of service, and guidelines for prevention and care in Australia. Therefore, it is now important to understand the risk for major CVD and risk factor profiles in immigrants compared to the Australian-born population, and how these factors change according to acculturation. This thesis specifically aims to better understand risk factor profiles and CVD in East Asian immigrants and the effect of increasing acculturation. METHODS: The thesis applied a variety of research methods to address these research aims. First, a systematic review of the literature and meta-analysis was performed to investigate the prevalence of smoking in East Asian populations living in western countries, and then to quantify the effect size for the association between acculturation and smoking prevalence in these populations. Second, a new cross-sectional study was designed and completed, and the data analysed in order to investigate and assess the factors related to vitamin D status, as a possible CVD risk factor, in East Asians living in Canberra. Third, I examined whether mathematical models used for the prediction of vitamin D status were valid and tested the accuracy of different ways of modelling the data to improve prediction, using data already collected in a case-control study as well as published data from the National Health and Nutrition Examination study. Last, an analysis of data from a population-based cohort study that was linked to hospital admissions and mortality records was conducted in order to assess CVD risk profiles according to region of birth and acculturation level and to investigate hospitalisation for CVD as East Asian immigrants become acculturated to the host country. RESULTS and DISCUSSION: The systematic review and meta-analysis of cross-sectional studies showed that East Asian-born women were far less likely to smoke than East Asian-born men and Australian-born individuals. The prevalence of smoking in East Asian-born men was high compared to western-born counterparts and smoking cessation was uncommon. However, the prevalence of current smoking was generally lower in men, but higher in women, compared to that of the native country and in association with longer duration of residence. Nevertheless, analysis of baseline cross-sectional data from the population-based 45 and Up Study, in Australia, showed that the prevalence of current smoking among Asian-born men was about the same as their Australian-born counterparts, and increased in relation to longer duration of residence. This contradicts the findings of the meta-analysis, and may be specific to Australia or specific to the 45 and Up Study, where the questionnaire was offered only in English, so that less acculturated immigrants may not have participated. The cross-sectional Asian Australian Health Study, based in Canberra, revealed that vitamin D deficiency in East Asian-born immigrants was common, and greater acculturation was associated with higher vitamin D status in this population. Higher vitamin D status was associated with a lower risk of hypercholesterolemia, but not other markers of cardiometabolic ill-health in this study. Because of the cross-sectional nature of the study, it is not possible to assess whether this is a causal association; it appeared to be mediated by physical activity. The studies testing the validity of prediction models for vitamin D status, as used in large health studies, showed that these may have poor prediction accuracy and a high risk of bias due to incorrect use of instrumental variables in the modelling. Furthermore, support vector regression modelling was shown to provide more accurate prediction of vitamin D status compared to multiple linear regression. The analysis of linked data from the population-based 45 and Up cohort study indicated that CVD risk factor profiles of East Asian immigrants tended to approximate those of Australian-born with increasing levels of acculturation. The association between region of birth and age at immigration to CVD risk varied across different types of CVD and was likely to be determined by a complex interaction of factors related to both the host country and the country of origin. CONCLUSIONS: This thesis explored the association between acculturation, putative CVD risk factors, CVD related hospitalisation, and all-cause mortality in East-Asian-born immigrants to western countries, mainly Australia. The risk of incident CVD incident is lower in EastAsian immigrant populations than in the Australian-born population. However, changes in the prevalence of various risk factors with increasing acculturation suggest that the pattern of CVD risk in Asian immigrants will change toward that of the Australian-born population over the coming years, as these immigrants become acculturated and adopt unhealthy diets and women are more likely to smoke, but there are healthier patterns of physical activity. Having identified these trends with acculturation, there are real opportunities, with targeted, culturally appropriate health promotion materials, to maximise the opportunities to make the transition to Australia one that improves, rather than detracts from, the health of this growing immigrant group.