Migration and Health: some introductory notes
I made a brief survey of the literature to get you started. Much of the following is drawn from the abstracts of recent articles.
“Global migration has dramatically increased over the past decade and is at an all-time high, approaching 200 million persons per year. Demographics and economic interdependence suggest that immigration will continue for the near future at record high levels.”
Nearly one-quarter of the refugees worldwide are children.
It is also estimated that there are 30-40 million undocumented migrant workers worldwide.
Categories of migration
Most commonly geographic, but some authors also mention ‘migration’ between socioeconomic groups. Geograpic mobility might be considered as horizontal, and social mobility as vertical; the two may be linked. For example, by moving to a new country an immigrant may open up opportunities or conversely may lose social status (PhDs driving cabs). Migration within countries, or between countries. In each case we may assess the extent of cultural change: how much adaptation is required to adjust to the new language and customs, etc? Migration may be voluntary, or necessary (as with refugees), versus forced (as with displacement). The impact on health (or the role that health played in stimulating the move) may be very different. Migration and age. Elderly people who move often do so because of the death of a spouse, or for health reasons. The impact of migration is therefore confounded with the impact of these other circumstances.
Marmot noted “Migrants bring their pattern of disease with them. This then changes towards that of the host country.” He described how people immigrating to UK from Ireland showed higher rates of heart disease than in UK, but following the familiar inverse relationship with SES. Meanwhile, immigrants from India showed no association between heart disease and social class, and those from the Caribbean showed higher rates among non-manual groups. These correspond to the stage in the epidemiologic transition in their country of origin. (Marmot M, Elliott P. Coronary heart disease epidemiology. Oxford University Press, 1992, p 15).
Lassetter & Callister undertook a literature review on the health of voluntary migrants to western societies. They included data on mortality and life expectancy, birth outcomes, risk of illness, CVD, BMI, hypertension, and depression. They reported wide variability, and many factors explain this variation: length of residence, acculturation, disease exposure, living conditions, behaviours, support networks, cultural and linguistic barriers, and quality of health care. Many migrants have better health than native-born persons, but the differential disappears over time. Migration should be viewed as an extended process with effects occurring years after physical relocation. (Lassetter JH, Callister LC. The impact of migration on the health of voluntary migrants in western societies. J Transcult Nurs. 2009 Jan;20(1):93-104).
There are innumerable studies, often presented in the context of the gene-environmental debate.
Balzi et al studied patterns of cancer in Italian immigrants: the first generation had lower risks of colon, breast and lung cancer than Canadian population. These rates change in their offspring to approximate the Canadian population. (Balzi D, et al. Cancer Causes and Control 1995; 6(1): 68-74).
Stellman & Wang showed the cancer profile for Chinese immigrants to New York was intermediate between people who remained in China and whites in NY. (Cancer 1994; 73(4): 1270-75)
Razum and Coebergh reviewed 37 studies of cancer among immigrants from non-western countries now residing in Western Europe. Overall, migrants showed a more favourable all-cancer morbidity and mortality compared with native populations, but with considerable site-specific risk diversity: migrants from non-western countries were more prone to cancers related to infections experienced in early life (liver, cervical and stomach). By contrast, migrants were less likely to suffer from cancers related to a western lifestyle (colorectal, breast and prostate). “This overview reaffirms the importance of exposures experienced during life course (before, during and after migration) for carcinogenesis.” (Arnold M, Razum O, Coebergh JW. Cancer risk diversity in non-western migrants to Europe: An overview of the literature. Eur J Cancer. 2010;46(14):2647-59).
And there is Ziegler's study of breast cancer among Chinese immigrant women, which suggests that the risk rises with the extent of contact with a western lifestyle:
A literature review of occupational injury and illness among immigrant populations showed higher rates of fatal and non-fatal injuries compared to native populations. This is in part due to immigrants working in higher risk occupations (e.g., agriculture, construction), but occupational morbidity and mortality is higher among immigrants than native-born workers even within occupational categories. (Schenker MB. A global perspective of migration and occupational health. Am J Ind Med. 2010 ;53(4):329-37.)
“High-risk occupations in which a large proportion of immigrant workers are hired include agriculture, sweatshops, day labourers, and construction.”
Oza-Frank et al. provide a synthesis of current literature on the relationship between immigrant duration of residence in the USA and body weight. Fourteen of 15 studies reported a significant, positive relationship between body mass index and duration of residence in the USA. Two studies reported a threshold effect of weight gain after 10 years of US residence, and another study reported that body mass index peaks after 21 years of duration for men and after 15 years for women. Prevention efforts may be more successful if where a person was born is considered beyond just their ethnicity. (Oza-Frank R, Cunningham SA. The weight of US residence among immigrants: a systematic review. Obes Rev. 2010;11(4):271-80).
Cross-sectional study using data from the 2000 National Health Interview Survey. Of 32,374 respondents, 14% were immigrants. The age- and sex-adjusted prevalence of obesity was 8% among immigrants living in the US for less than 1 year, but 19% among those living there for 15+ years. Immigrants were also less likely than US-born to report discussing diet (18% vs 24%, P<.001) and exercise with clinicians (19% vs 23%, P<.001). (Goel MS, McCarthy EP, Phillips RS, Wee CC. Obesity among US immigrant subgroups by duration of residence. JAMA. 2004;292(23):2860-7).
Evidently, population mobility is a major factor in the globalization of public health threats and risks, such as the distribution of antimicrobial drug-resistant organisms. Drug resistance poses a major risk in health care settings and is emerging as a problem in community-acquired infections.
The findings for birth outcomes are very varied: some migrant groups have similar or better birth outcomes than women from the receiving country, while other studies show raised risk of adverse birth outcomes. And yet, immigration of women of childbearing age has made their perinatal health status a priority for governments. The migration literature is extensive, but the heterogeneity of study designs and definitions of migrants limits the conclusions that can be drawn.
A systematic review of studies of stillbirths and infant deaths following migration illustrated these discrepant findings. 53% of the studies reported worse mortality outcomes, 35% reported no differences and a few (13%) reported better outcomes for births to migrants compared to the receiving country population.
• Refugees were the most vulnerable group.
• Among non-refugees, non-European migrants in Europe and foreign-born blacks in the US had the highest excess mortality.
• In general, adjustment of background factors did not explain the increased mortality rate among migrants.
• Higher preterm birth rates explained the increased mortality figures among some migrant groups. The increased mortality from congenital anomalies may be related to restricted access to screening, but also to differing attitudes to screening and termination of pregnancy.
CONCLUSIONS: Mortality risk among babies born to migrants is not consistently higher, but appears to be greatest among refugees, non-European migrants to Europe, and foreign-born blacks in the US. (Gissler M, Alexander S, et al. Stillbirths and infant deaths among migrants in industrialized countries. Acta Obstet Gynecol Scand. 2009;88(2):134-48).
A systematic review and meta-regression analyses were conducted using three-level logistic models to account for the heterogeneity between studies and between subgroups within studies. Twenty-four studies, involving more than 30 million singleton births, were included.
Compared with US-born women:
• Black migrant women were at lower odds of delivering LBW and preterm birth babies.
• Hispanic migrants also exhibited lower odds for these outcomes
• South-central Asians were at higher odds of delivering LBW babies.
(Urquia ML, Glazier RH, et al. International migration and adverse birth outcomes: role of ethnicity, region of origin and destination. J Epidemiol Community Health. 2010;64(3):243-51).
Gagnon et al ran a meta-analysis of 23 studies covering pregnancy and birth outcomes among migrant women. About half of the studies found that migrants' rates of preterm birth, low birth weight and health-promoting behaviour were as good or better as those for receiving-country women. Meta-analyses found that Asian, North African and sub-Saharan African migrants were at greater risk of feto-infant mortality than women in the receiving populations, and Asian and sub-Saharan African migrants were at greater risk of preterm birth. (Gagnon AJ, Zimbeck M, et al. Migration to western industrialised countries and perinatal health: a systematic review. Soc Sci Med. 2009;69(6):934-46).
A Cochrane review of mental distress in refugee children included 22 studies, covering 3,003 children from over 40 countries. Studies varied in definition and measurement of problems, which included levels of post-traumatic stress disorder from 19 to 54%, depression from 3 to 30%, and varying degrees of emotional and behavioural problems. Significant factors influencing levels of distress appear to include demographic variables, cumulative traumatic pre-migration experiences, and post-migration stressors. There is a need for contextual and methodological refinement so that future research has greater generalizability and clinical implications. (Bronstein I, Montgomery P. Psychological Distress in Refugee Children: A Systematic Review. Clin Child Fam Psychol Rev. 2010 Dec 23).
McGrath et al. reviewed 161 studies from 33 countries reporting original data on the incidence of schizophrenia (published in 1965-2001). The median schizophrenia prevalence was 15.2 per 100,000 (10th to 90th centile range, 7.7 - 43.0). Rates were higher in males (rate ratio 1.4).
Rates in migrants were higher compared to native-born: median rate ratio 4.6 (1.0-12.8). (McGrath J, Saha S, Welham J, El Saadi O, MacCauley C, Chant D. A systematic review of the incidence of schizophrenia: the distribution of rates and the influence of sex, urbanicity, migrant status and methodology. BMC Med. 2004; 28(2):13).
In a Canadian study, Clarke et al. suggested that a sense of community belonging may moderate suicidality in some immigrant groups. Francophone whites and Aboriginals were more likely to report suicidality compared to Anglophone whites whereas visible minorities and foreign-born whites were least likely. Disadvantages in SES, and its combined effect with depression and alcohol use led to high rates even among the low-risk visible minority group. However, the sense of community belonging buffered the risk for suicidality across pathways. (Clarke DE, Colantonio A, Rhodes AE, Escobar M. Pathways to suicidality across ethnic groups in Canadian adults: the possible role of social stress. Psychol Med. 2008 Mar;38(3):419-31).
And even Asthma
Asthma has emerged as an important public health problem in many Latin American countries over the past decade. It is associated particularly with underprivileged populations living in cities but remains relatively rare in many rural populations. The causes of asthma in Latin America are associated with urbanization, migration, and the adoption of a modern 'Westernized' lifestyle and environmental changes, including changes in diet, physical activity, hygiene, and exposures to allergens, irritants, and outdoor and indoor pollutants. (Cooper PJ, Rodrigues LC, Cruz AA, Barreto ML. Asthma in Latin America: a public heath challenge and research opportunity. Allergy. 2009;64(1):5-17).
Culturally and linguistically diverse migrants must assimilate and adapt to their new surroundings, discover different cultures and customs, and embrace a new way of life. A number of studies have documented that acculturation to western society is linked to an increase in blood pressure (BP) and to worse cardiovascular health. A meta-analysis reviewed 125 relevant manuscripts. Measures of association (using effect sizes) were extracted for SBP and DBP readings.
• The effect sizes associated with acculturation were 0.28 for SBP and 0.30 for DBP, with increasing acculturation to western society related to higher BP.
• More acculturated individuals had an average of 4 mm Hg higher BP than less acculturated individuals, which is similar to the effect sizes of known risk factors for high BP such as diet and physical activity.
• The effects appear to be universal, with similar effect sizes found across all regions of the world.
• Change in BP due to acculturation was not related to body mass index (BMI) or cholesterol but was related to length of residence in the new culture, with the largest effect sizes seen on initial entry and then decreasing rapidly within the first few years. Sudden cultural changes, such as migration from rural to urban settings, resulted in the largest effect sizes, which finding supports the hypothesis that the stress of cultural change is important role in the acculturation effect.
CONCLUSIONS: Acculturation to western society is associated with higher BP, and the distress associated with cultural change appears to be more influential than changes in diet or physical activity. (Steffen PR, Smith TB, Larson M, Butler L. Acculturation to Western society as a risk factor for high blood pressure: a meta-analytic review. Psychosom Med. 2006;68(3):386-97).
A 2009 literature review of 57 publications on the health of migrants focused on physical inactivity and showed that it is relatively common in migrant groups, and forms a key risk factor for chronic disease for imigrant groups. Challenges and barriers that limited participation in physical activity include cultural and religious beliefs, issues with social relationships, affordability, environmental barriers, and perceptions of health and injury. (Caperchione CM, Kolt GS, Mummery WK. Physical activity in culturally and linguistically diverse migrant groups to Western society: a review of barriers, enablers and experiences. Sports Med. 2009;39(3):167-77).
Measurement Challenges in Acculturation
A systematic review of 134 studies noted considerable variation in definition and measurement of acculturation. The ten acculturation scales reviewed provided little theoretical orientation. Most measures focus on language acquisition and ignore acculturative changes in attitudes, beliefs and behaviours. (Thomson MD, Hoffman-Goetz L. Defining and measuring acculturation: a systematic review of public health studies with Hispanic populations in the United States. Soc Sci Med. 2009 Oct;69(7):983-91).
Similarly, Salant and Lauderdale emphasize the need to recognize the diversity of Asian immigrant populations in different receiving countries. They critically examined the conceptualizations and measurement of acculturation, emphasizing the great diversity among the category ‘Asian immigrants’. (Salant T, Lauderdale DS. Measuring culture: a critical review of acculturation and health in Asian immigrant populations. Soc Sci Med. 2003;57(1):71-90).
A “Cultural Gradient”?
A social gradient has been consistently demonstrated in Western countries with higher socioeconomic status (SES) related to lower blood pressure (BP). In non-Western countries, however, the social gradient is not always evident, with some countries appearing to show a reversed social gradient. It was hypothesized that culture moderates the social gradient, with the relationship between SES and BP differing as a function of culture. To investigate the idea of a "cultural gradient" a sample of Hispanic immigrants and Whites was studied. A total of 79 participants (30 Hispanic immigrant, 49 White) wore ambulatory blood pressure monitors for 24 h. The Hispanic immigrants also completed the Acculturation Rating Scale for Mexican Americans-II. Hispanic immigrants had lower SES and lower BP compared to Whites. A cultural gradient moderating the social gradient was evident with Hispanic immigrants displaying a positive relationship between SES and BP and Whites displaying a negative relationship. Among Hispanic immigrants, increased acculturation to Western culture decreased the positive relationship between SES and BP. Just as there is a social gradient with increasing socioeconomic status related to better cardiovascular health, there appears to be a cultural gradient with increasing acculturation to Western society related to worse cardiovascular health. (Steffen PR. The cultural gradient: culture moderates the relationship between socioeconomic status (SES) and ambulatory blood pressure. J Behav Med. 2006 Dec;29(6):501-10).
The Nutrition Transition?
Satia reviewed concepts of "dietary acculturation" and the "nutrition transition". These highlight the co-existence of high rates of malnutrition in developing countries along with a new emergence of dietary excess, sedentary behaviour, obesity, and other chronic diseases in middle- and upper-class persons who migrate to richer countries. (Satia JA. Dietary acculturation and the nutrition transition: an overview. Appl Physiol Nutr Metab. 2010 Apr;35(2):219-23).
There are Always Exceptions!
A systematic search of literature examined the health of North African migrants to France showed that in France, as in other host countries, migrants belong to the lowest socio-economic strata. But they have on average better health and lower mortality than the local-born population. Health benefits are particularly noticeable in Mediterranean men, especially for affluence-related diseases such as cancer and cardiovascular diseases. Adult migrants from southern Europe and North Africa report dietary practices consistent with the typical Mediterranean diet, which is renowned for its positive effects on health.
And yet, North African men smoke as heavily as the local-born of the same occupational categories, but their mortality rates from lung cancer are notably lower. This paradox may be the result of a synergy between different phenomena such as the selection of the fittest applicants for immigration and the maintenance of healthy lifestyles from the countries of origin.
By contrast, migrant women do not enjoy the same health advantages, possibly because they are less likely to be selected on the basis of their health and because they often do not work.
CONCLUSIONS: The diet of Mediterranean adults living in France may partly explain the low rates of chronic diseases and high adult life expectancy observed in migrant men from northern Africa. (Darmon N, Khlat M. An overview of the health status of migrants in France, in relation to their dietary practices. Public Health Nutr. 2001 Apr;4(2):163-72).
Here is Yoko Schreiber's presentation.
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