By: Hiranthi Jayaweera, Senior Researcher
The Global Burden of Disease study 2010, funded by the Bill & Melinda Gates Foundation, is a comprehensive assessment of data on current patterns of disease, injury and risk throughout the world. Some of its main findings, published recently in The Lancet, are that while there has been much progress in population health since the last study in 1990, with for instance increasing life expectancy, decreasing child mortality and the reduction in some infectious diseases, the global burden of non-communicable (chronic) diseases such as cancer, diabetes, and heart disease and stroke, has considerably increased, with implications for disability as well as for mortality. Where does migration, and particularly international migration, fit in this global pattern of increasing risk and prevalence of non-communicable diseases (NCDs)?
Migrant focus: NCD’s vs. infectious diseases
There are very significant health implications of mobility for the ever growing numbers and diversity of migrants worldwide – for example exposure to health hazards associated with migrant journeys and working and living conditions in receiving societies; legal restrictions and structural barriers to universal access to necessary healthcare. But within the broad policy and research focus around migrants’ health today, there is arguably less emphasis on NCDs compared to infectious diseases like TB and HIV/AIDS.
The higher prevalence of some infectious diseases among some migrant groups compared to the native population, and therefore newly arriving migrants being characterised as carriers of these diseases despite evidence of the association between underlying poverty and deprivation, and disease transmission in receiving contexts, have been at the forefront of public health concerns. These concerns are also linked at one end of the spectrum to more restrictive immigration controls in receiving societies especially in the global north, and at the other end to debates around providing free and easy access to health services irrespective of legality of immigration status.
Country of birth, ethnicity, and mortality in the UK
There is evidence of country of birth and ethnic differences in NCDs in the UK: for instance, higher rates of both hospitalisation and mortality among men and women of South Asian, compared to ‘non-South Asian’, origin for myocardial infarction (heart attack) in Scotland; a higher prevalence of doctor-diagnosed Type II diabetes among African-Caribbean, Indian, Bangladeshi, and Pakistani men and women compared to the general population in England; and a lower risk of getting cancer when all cancers are combined, for Asians, Chinese and Mixed ethnic groups in England compared to Whites, although there is a higher risk of some specific cancers for minority ethnic groups. While mortality data (death registration) in the UK is according to country of birth, incidence and prevalence data is by ethnicity, which makes it difficult to understand NCD patterns among migrants.
The healthy migrant: deterioration and health care resources
In some contrast to infectious diseases, health concerns and academic debates around migration and NCDs tend to relate to ideas on ‘the healthy migrant effect’– that those who migrate are generally healthy compared to non-migrant populations both in sending and receiving countries, but as migrants adopt risky health behaviours characteristic of receiving societies, their health deteriorates over time. In the case of NCDs such as heart disease, diabetes and some cancers, health risks include smoking, alcohol consumption, poor diet linked with obesity, and lack of exercise. There is also concern that the growing prevalence of NCDs among some migrant/minority groups places an increasing burden on health care resources in destination countries, especially also as the evidence suggests that children born to migrants in receiving countries are likely to exhibit similar disease patterns.
Migration and the epidemiology of NCD’s
In a recent article, Zaman and Bhopal brought out important factors associated with the prevalence and risk of coronary disease among South Asians in the UK. They found that:
- There is a high incidence of coronary disease but the survival rate among South Asians with the disease was better than among Whites – which suggests that the healthcare they receive is positive. One implication of this pattern is that unless there is a focus on primary prevention, the pool of South Asians with the disease is likely to increase, particularly given the ageing of the UK population as a whole.
- Biological, as well as socio-economic and behavioural determinants underlie high rates of coronary disease among South Asians, and it is also very important to take differences in risk factors within South Asians as a group into consideration – for instance, high smoking rates among Bangladeshi men taking into account the relatively high levels of social deprivation among Bangladeshis in Britain (but note the very low smoking prevalence among Bangladeshi women).
- Behavioural risk factors such as physical inactivity and unhealthy diets extend into the second generation (the children of South Asian migrants who are now themselves reaching middle age).
Evidence-based studies such as this contribute immensely to furthering our understanding of the epidemiology of NCDs including migration dynamics. As commentary, a couple of important issues are worth bearing in mind.
First, as critiques of the acculturation model applied to health have noted, the adoption of receiving society health-related attitudes and behaviour by migrants is far from a one-directional, linear process. As the above study showed as well, it is important to make clear who we are talking about – e.g. disaggregate the category ‘South Asian’ often used in reporting NCD rates and patterns, by socio-economic position, sex, age, national origin, religion etc. – and whose (similarly disaggregated) risky health behaviours in receiving societies are taken on by migrants, if at all. An understanding of the framework of structural constraints surrounding choice in health behaviour for migrants who are poor and living in deprived areas – e.g. the economics and geography of access to good quality and nutritional food in preventing obesity – is also imperative.
A second and related question is: to what extent is migration a leading factor in the global phenomenon of increasing NCD rates demonstrated in the results of the GBD study mentioned at the beginning of this piece? Forty years ago Omran put forward the theory of ‘epidemiological transition’ whereby all over the world man-made degenerative diseases replace infection as the primary cause of mortality and morbidity because of factors such as changes in the environment interacting with biology, patterns of socio-economic change, developments in biotechnology and public health.
Research findings in countries of origin of key migrant categories in the affluent countries of the global north attest to the high and growing prevalence and risk of NCDs such as cardiovascular disease (CVD) and diabetes in domestic populations. For instance a population based survey in Sri Lanka showed both high national rates of hypertension (high blood pressure), diabetes and obesity as key risk factors for CVD and regional and sex differences in the prevalence of these conditions. Such findings demonstrate how important it is to consider broader sending contexts including social determinants of health in local populations and areas, and the pre-migration health of those who are mobile, in understanding patterns of and reasons for NCD prevalence among migrants and their children in receiving contexts.
It is also important to bear in mind that in the UK while treatment for infectious diseases such as TB and HIV is free for all irrespective of immigration status, hospital treatment for NCDs is only free for legal residents, thus leaving a potentially substantial segment of the migrant population without the healthcare they need. More comprehensive knowledge about risks and patterns of NCDs among diverse migrant categories is imperative for informing, and helping target, health policy and practice towards reducing the mortality and disability costs of NCDs in the whole population.