1 Institut National dEtudes Démographiques, 133 Bd. Davout, 75980 Paris Cedex 20, France. E-mail: khlat{at}ined.fr
2 Institut National de la Santé et de la Recherche Médicale/Institut Scientifique et Technique de la Nutrition et de lAlimentation, 5 rue du Vert-Bois, 75003 Paris, France.
SirsCompared with non-Hispanic Whites, Hispanics in the US are poorer and less educated, and yet they enjoy a lower all-cause mortality rate. This so-called Hispanic Paradox has received much attention over the past 20 years, both in the epidemiological and demographic literature. Besides artefactual explanations (i.e. possible under-reporting of Hispanic deaths on death certificates), competing theories fall into two categories: the salmon bias hypothesis, according to which migrants are likely to return to their country of origin after they retire or become seriously ill, and, the healthy migrant hypothesis, according to which those who migrate and remain in the host country are the healthiest and strongest members of their population of origin.
To date, two reviews have documented extensively the wealth of literature on the Hispanic paradox. One, which is very critical of the concept, focuses on low birthweight and infant mortality;1 the other, which is relatively supportive, covers all the different health components involved in the paradox (mortality, infant mortality, violence, AIDS, coronary heart disease, stroke, cancer, and diabetes).2 The first concludes that the evidence supporting the paradox is fragile and highlights the potential role of selective processes in explaining the migrants advantage, while the second puts forward the complexity of the picture, with variations by age, gender, type of Hispanic group, degree of acculturation, and specific disease or cause of death.
Recently, a paperto be considered as a landmark in the fieldhas very elegantly established that neither the salmon bias, nor the selection of healthy Hispanic migrants into the US could explain the mortality advantage of the Hispanics, and called for further research on cultural factors, especially those involving favourable health behaviours, to shed more light on this issue.3 While much controversy surrounds the very existence and interpretations of the Hispanic paradox, it has been argued that investigation of this "paradox" may provide additional insights into the ways that social factors affect the health of the population at-large,2 and that the Hispanic paradox should be a motivator for further research ....1
With this in mind, our purpose is to place the Hispanic paradox in a wider geographical and cultural perspective, by pinpointing the remarkable mortality advantage that some Mediterranean migrant groups enjoy in Germany and France. While the literature on migrants mortality is relatively scarce in Europe, two methodologically sound studies have provided quite an unexpected picture. In Germany, analysis of register data has established that the age-adjusted mortality of the 2 million Turkish residents was consistently half that of the Germans, and also less than half that of an urban population in Turkey.4 The former findings, which concerned males and females equally, were confirmed by a cohort study (German Socio-Economic Panel) unlikely to be subject to the inaccuracies of denominator figures.5 Convergent features have emerged from a study based on register and census data in France which highlighted the surprisingly low mortality of Moroccan immigrants, whose number had swollen in the early 1980s to nearly 600 000.6 Using an indirect demographic method originally devised to estimate the completeness of vital statistics in developing countries, the authors have found that the proportion of missing deaths among Moroccans was about 23% for men, and negligible for women. After having corrected the numbers of male deaths accordingly, they found an adjusted life expectancy of 73.7 years in the 1980s, as opposed to 71.3 in the French population, and 78.8 in females as opposed to 79.6 in the French population. And yet, the socio-demographic profile of those migrantsthey are frequently illiterate, single, and employed largely as manual workers (83%)is expected to favour higher mortality.
Echoing the Hispanic mortality paradox in the US, the above findings convincingly set the case for a Mediterranean migrants mortality paradox in some Western European countries, and have led to a questioning of the classical interpretations prevalent in the epidemiological and demographic literature. Rather than referring to a salmon bias, the authors of the European studies have wondered about the existence of a mobility bias resulting from an inflation of the denominator base, due to migrants often returning to their home country for short or long periods, be it in relation to their health status or not. Indeed, the Mediterranean countries of Southern Europe and North Africa are geographically close to France and Germany, and migrants often return to their home country during holidays or for family reasons. Individual follow-up such as that implemented in the German Socio-Economic Panel provides strong support for the substantive nature of the mortality advantage, as does the persistence of a substantial under-mortality in the Moroccans study after correction for under-registration of deaths. Possible explanations are then either the role of selective processes (healthy migrant hypothesis) or that of health-protective behaviours.
The healthy migrant hypothesis is particularly difficult to investigate: first, mortality estimates in countries of origin are not always available for comparative purposes; second, even when they are, differences in health care between countries render the comparisons meaningless, and; third, the regions of origin of the migrants in their home countries are likely to be different in their mortality profile from the national average. In Abraido-Lanza et al.s paper,3 the mortality rates in Puerto Rico, Cuba, and Mexico were found to be lower than those of the US, and this was interpreted by the authors as consistent with a cultural explanation of the Latino mortality paradox. Those comparisons, however, were not very convincing, given that, as pointed out by Landen,7 they involved crude rather than age-standardized mortality rates. In Europe, the French study is the only one which has incorporated comparisons with the country of origin of the migrants (Morocco). The picture which emerges is that of a much higher life expectancy for the migrants than that estimated for the population of Morocco: the gain in life expectancy was 9.9 years for men, and 11.6 years for women. This may reflect the healthy migrant hypothesis, but not necessarily. Generally speaking, international comparisons are extremely difficult to interpret, with countries differing in numerous factors which influence all-cause mortality, among which are social class, economic indicators, and effectiveness and accessibility of health care and other services.8
In addition, one may legitimately wonder to what extent the selection of applicants for immigration on the basis of their health is a plausible explanation of the mortality paradox. Indeed, two questions are left unanswered: first, do the health selection effects persist long enough to explain a mortality advantage decades after it has taken place, and second, if the migrants are healthier at entry, what are the factors underlying their superior health? Concerning the first point, surprisingly little has been published. Study of an industrial cohort in Great Britain has shown that the healthy worker effect was no longer visible 15 years after entry in the cohort,9 while conversely an analysis of the Assets and Health Dynamics of the Oldest Old (AHEAD) in the US concludes that good health of a population at young ages is maintained throughout the lifespan.10 As for Hispanics, the literature indicates that their health and health behaviours deteriorate with acculturation.11 Clearly, more empirical and theoretical studies are needed.
Supposing health selection is the key explanation to the mortality advantage, then what are the factors underlying the superior health of the migrants? Do they have lower mortality rates just because the health checks have filtered out the disabled and chronically ill? Or do they have more favourable health behaviours? According to Uitenbroek and Verhoeff,12 who have investigated mortality of the Mediterranean migrants in Amsterdam, selection at entry is not a convincing explanation for their remarkable life expectancy. Indeed, in their twenties and early thirties symptoms of the major causes of death, i.e. cancers and cardiovascular disease are rarely present, and it is difficult to imagine how these young people could have been selected on their future susceptibility to those diseases. Those authors, in accord with Razum et al.4 are more supportive of the unhealthy re-migration hypothesis; in fact a more elaborated version of the salmon bias hypothesis which assumes that migrants who re-migrate are those who do not cope well socially and economically, and that those migrants are more likely to experience higher mortality in the future. This can be viewed as a kind of indirect selection on factors connected to both socio-occupational skills and health capital, similar to that which has been conceptualized regarding unemployment:13 the mechanism would be that both unemployment and health are related to a certain personality trait. Could we imagine also that an indirect selection is involved in the migration process, with factors connected to both the will and capacity to migrate and to health? In relation to the salmon bias concept, Razum et al.4 also question the plausibility of re-migration of severely ill migrants, considering that it is unlikely that Turkish residents return to their home country when they suffer from conditions such as cardiovascular disease for which medical treatment in Germany is readily available and almost free. Economic considerations could therefore deter sick migrants from going home, unless they are moribund, but in this case do they have the strength to undertake a journey back home?
Abraido-Lanza et al. consider that the role of cultural factors involving favourable health behaviours is an attractive hypothesis to be tested. If it is confirmed, then this would mean that the migrants would be benefiting from the best of both worlds:14 the favourable habits of their country of origin and the efficiency of the health care system of their host country. Of the two studies in Europe, the one which has examined causes of death and gathered data on health-related habits is the French one, and the results are quite mixed: on one hand, the death rates from cancers and cardiovascular diseases are much lower among Moroccan males than in the French population, on the other hand, their lifetime consumption of tobacco is comparable, though there are indications that their nutritional habits could be more favourable.15 One important feature of the Moroccan community in France is that they drink very little alcohol, and this could play a major role in their mortality advantage: of all countries in the European Community, France is the one with the highest percentage of heavy alcohol drinkers, and it is characterized by a high alcohol-related premature mortality. There might be cohort effects involved in the lower lung cancer mortality of the Moroccans in France, with heavy smoking limited to the younger cohorts who have not yet reached the age at which lung cancer rates start to rise. Also, a role for alcohol consumption in lung cancer aetiology has been suggested in some studies,16 and one may wonder whether Moroccans are protected from lung cancer in part because they drink very little alcohol. Lastly, the potential role of differential exposure to genetic factors of susceptibility to lung cancer17 is worthy of consideration. Greeks in Australia are another Mediterranean migrant group which was found to have an exceptionally high life expectancy in spite of continuing high rates of cigarette smoking, and this was attributed to the offsetting effects of the Mediterranean diet.14
One of the reviews of the Hispanic paradox concluded by saying that there was a reasonable degree of certainty that the paradox was real for some subgroups, among them older Hispanics.2 In France and Germany, the older cohorts of migrants were precisely those which had the most difficult and hazardous working conditions,18,19 in the mines and the automobile industry. They would, therefore, be expected to have higher mortality. In fact, this was the case for migrants from Eastern European countries but not for Mediterranean migrants.20 To date, the causes of the paradox are largely unknown, be it in the US or in Europe, and, as pointed out by Franzini et al.:
if the reasons are largely cultural, then the paradox will only exist for as long as a large percentage of Hispanics remain culturally distinct from the rest of the US ... a rare window of opportunity now exists to learn more about how cultural factors influence ones health....2
The migrants mortality paradox raises challenging questions about the nature of the selective processes related to migration, and those questions have a bearing on health-based selection in general and on the potential role of indirect selection in explaining part of the association between socio-demographic factors and health.
The opening up of new research avenues is desirable to meet the challenge, along the lines recently delineated by Schwartz, Susser, and Susser.21 More attention should be paid to the historical context of migration and the past living conditions of the different waves of migrants, before and after migration, and to the legal and jurisdictional aspects of re-migration. Shifting the emphasis from individual-based studies to studies of communities as a whole and of the cultural factors that are related to management of health and disease may provide explanatory leads. As pointed out by Palloni,1 studies of migrants in their host countries should be complemented by:
studies of the sending populations, including those people who have returned after being migrants, those who could have been migrants but were not, and those who tried unsuccessfully to be migrants.
Also, qualitative studies are potentially very informative with respect to the acculturation process and its health-related aspects, to the cultural representations of health, and the range of motives for re-migration. Last but not least, an international perspective on the subject would throw new light on the hows and whys of this enduring epidemiological enigma.
References
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