Cardiovascular disease in East Asian immigrants living in Australia: considerations in relation to vitamin D deficiency, smoking and acculturation
Date
2016
Authors
Guo, Shuyu
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Abstract
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.
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Cardiovascular disease, East Asian immigrants, vitamin D deficiency, smoking, acculturation
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