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Lower circulatory disease mortality among Australian South Asians
- Linsay Gray, Seeromanie Harding and Alison Reid (11 June 2007)
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Lower circulatory disease mortality among Australian South Asians: how do we explain the paradox?
- Charles Agyemang, Raj Bhopal, Karien Stronks (14 May 2007)
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Linsay Gray, Research Associate MRC Social and Public Health Sciences Unit, 4 Lilybank Gardens, Glasgow, G12 8RZ, Seeromanie Harding and Alison Reid
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Lower mortality and selection As discussed in our paper (1), we agree with Agyemang et al (2) that the low cardiovascular mortality of South Asians (and most migrant groups) in Australia is influenced by the selection process imposed by its immigration laws. What is interesting, however, is the retention of that low risk even after three decades of living in Australia when selection effects would be less important as people acculturate to the host experience. We cited the contrasting findings for South Asian migrants in UK, among cardiovascular mortality increased after about 15-20 years of residence. It is worth mentioning that in that study, excess mortality was observed only among those with long residence (3). Occupational class as a measure of socio-economic status (SES) The measurement of SES among migrants is complex, and linked to the difficulties of making use of educational qualifications and experience. In our analyses we were unable to use additional measures of SES to occupational class (e.g. education, overcrowding) as, although this information is collected in the census, it is not recorded at death registration (4). Higher proportions of South Asians in a non-manual class compared with Australia-born correspond with reported higher median income (5). In our study, increasing residence was associated with a greater likelihood of being in a non-manual class, and the effect of class on mortality became larger with increasing duration of residence. Thus, although there are difficulties in applying occupational class, adjusting for it is nevertheless appropriate. Australian environment and migrants Australia-born in our study included those of Aboriginal ethnicity. The protective “Australian environment” referred to the experience of Australia for migrants and so the circulatory disease death rates for Aborigines are not relevant in this context. Whereas the Aboriginal experience reflects social exclusion for over 200 years (6), that of migrants is strikingly different with active support for a range of services since the 1940s (5). These include settlement services for newly arrived migrants (e.g. English tuition, accommodation for refugees and migrants at hostels and flats) and continuing support for community programs. Insofar as the Australian environment impacts on the experience of everyone living in Australia, the Aborigines are relevant but form a very small proportion (around 2%) of the Australia-born category. Migrants are likely to be more similar in their experience of Australia to the majority of the Australia-born category. In an era of striving for molecular answers to ethnic differences in disease, there is clearly a case for comparative studies to help us understand how some settings, such as Australia’s, promote healthy environments for migrants, while others, such as in the US and UK, apparently impair migrant health. References 1. Gray L, Harding S, Reid A. Evidence of divergence with duration of residence in circulatory disease mortality in migrants to Australia. European Journal of Public Health. 2007 Mar 12. 2. Agyemang C, Bhopal R, Stronks K. Lower circulatory disease mortality among Australian South Asians: how do we explain the paradox? European Journal of Public Health; 2007. 3. Harding S. Epidemiological paradox of cardiovascular disease in Black Caribbeans and South Asians: evidence from national surveys implies a shift across generations. ESDS Government Research Conference, Understanding Coronary Heart Disease: evidence from survey data London 2004: http://www.ccsr.ac.uk/esds/events/2004-10-29/slides/index.html (last accessed 07/06/2007). 4. Deaths Australia 2004. Canberra: Australian Bureau of Statistics; 2005. 5. Young C. Health and welfare of immigrants and access to services in Australia. Scand J Soc Welfare 1994;3:121-32. 6. Hunter B. Taming the social capital hydra? Indigenous poverty, social capital theory and measurement. Canberra: Centre for Aboriginal Economic Policy Research, The Australian National University; 2004. Conflict of Interest:None declared |
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Charles Agyemang, Associate Researcher Department of Social Medicine, Academic Medical Centre, University of Amsterdam, 1100 DD Amsterdam,, Raj Bhopal, Karien Stronks
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Cardiovascular disease (CVD) is a major public health problem and some minority ethnic groups are disproportionately affected. People with ancestral origins in the Indian Subcontinent (henceforth, South-Asians), for example, are highly susceptible to CVD after migration to urban settings, particularly overseas.[1] South-Asians in the UK, for example, have a 50% greater risk of dying prematurely from CHD than the general population.[2] Such differences still remain an epidemiology puzzle, despite widespread debate and considerable research. We, therefore, read with interest the recent Australian findings reported in this journal by Gray and colleagues.[3] Their finding is a very rare example of the circulatory disease mortality being relatively low in South-Asians overseas. This finding challenges the popular notion of South-Asians being particularly susceptible to CVD in urban environments, and raises several questions. For example, is the lower circulatory disease mortality found in South-Asians in Australia due to selection bias? Is the Australian environment more favourable to South- Asians than other countries’ environment? Or is this finding a mere statistical artefact? Alternatively, is it a reflection of differences in the composition of the migrant populations, for example, with regard to socio-economic status (SES)? The association between low SES and higher cardiovascular mortality[4] and risk factors[5] has emerged in South-Asians, as summarised by Bhopal et al.[2] A greater proportion of Australia's migrants are chosen on the basis of their skills than in many other host countries. It is likely that South -Asians in Australia have a better SES than their counterparts’ elsewhere, hence better health outcomes. Although Gray et al. controlled for occupational class, this is not a very sensitive indicator for SES in South-Asians.[5,6] The skilled South-Asians in Australia may have a greater awareness of CVD risk factors and are in better position to access health care than their counterparts elsewhere. This may reflect the contrasting results found between South-Asians in Australia, and the UK, and their siblings in India.[7-8] Mahajan and Bermingham, for example, found South-Asians in Australia to have a more favourable CVD risk profile than their siblings in India.[7] In contrast, Bhatnagar et al. found the UK Punjabis to have an unfavourable CVD risk profile than their siblings in India.[8] The ethnic composition of the Australia-born group in Gray et al. is also unclear. One study, for example, found a significant decrease in deaths from circulatory diseases among non-Aborigines, but not among Aborigines in Western Australia between 1985-89 and 1990-94.[9] These findings clearly indicate that Gray et al’s[3] findings needs to be interpreted with caution, especially the assertion that the Australian environment is protective of circulatory diseases. Nevertheless, Gray et al’s study has important public health implications. For one, it may indicate that South-Asians are not programmed to develop circulatory diseases overseas and that the influence of socio-economic position in the host countries may be more important than it is widely accepted. It also reiterates the need for international comparison studies to investigate the role of the host country environment on ethnic inequalities in health. Overall, we judge that the paradox is most likely explained by the high SES of South-Asians in Australia, and a favourable cardiovascular risk profile-the two being interlinked. References 1. Patel K and Bhopal R. The epidemic of coronary heart disease in South Asian populations: causes and consequences. South Asian Health Foundation, Birmingham 2003. 2. Gill PS, Kai J, Bhopal RS, Wild S. Health care needs assessment: black and minority ethnic groups. In: Stevens A, Raftery J, Mant JM (eds). Health Care Needs Assessment. The epidemiologically based needs assessment reviews. Third Series. Radcliffe Medical Press: Oxford (http://hcna.radcliffe-oxford.- com/bemgframe.htm). 3. Gray L, Harding S, Reid A. Evidence of divergence with duration of residence in circulatory disease mortality in migrants to Australia. Eur J Public Health. 2007 Mar 12; [Epub ahead of print] 4. Harding S, Maxwell R. Differences in mortality of migrants. In: Drever F, Whitehead M, Editors. Health inequalities. London. Office for National Statistics 1997108-121. 5. Bhopal R, Hayes L, White M, Unwin N, Harland J, Ayis S, Alberti G. Ethnic and socio-economic inequalities in coronary heart disease, diabetes and risk factors in Europeans and South Asians. J Public Health Med. 2002; 24(2):95-105. 6. Nazroo JY. South Asian people and heart disease: an assessment of the importance of socioeconomic position. Ethn Dis. 2001 Autumn;11(3):401- 11. 7. Mahajan D, Bermingham MA. Risk factors for coronary heart disease in two similar Indian population groups, one residing in India, and the other in Sydney, Australia. Eur J Clin Nutr. 2004; 58(5):751-60. 8. Bhatnagar D, Anand IS, Durrington PN, Patel DJ, Wander GS, Mackness MI, Creed F, Tomenson B, Chandrashekhar Y, Winterbotham M, et al. Coronary risk factors in people from the Indian subcontinent living in west London and their siblings in India. Lancet. 1995; 345(8947):405-9. 9. Gracey M, Williams P, Smith P. Aboriginal deaths in Western Australia: 1985-89 and 1990-94. Aust N Z J Public Health. 2000; 24(2):145- 52. Conflict of Interest:None declared |
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