Introduction, findings, and conclusions

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Introduction

In recent years, annual immigration to Canada has totalled more than 230,000.¹ About two-thirds (69.3%) of the 1.6 million increase in the Canadian population between 2001 and 2006 was attributable to immigration. By 2006, immigrants made up one-fifth (19.8%) of the population, a percentage that is expected to reach 25% to 28% by 2031.²

The health and the health care needs of this large and growing share of the population are not necessarily the same as those of people born in Canada.^{3, 4} Earlier studies have found a "healthy immigrant effect"; specifically, immigrants' health is better than that of the Canadian-born, but it tends to decline as their years in Canada increase.^{5, 6} This reduction in immigrants' health advantage is apparent in self-reported general health,^{7, 8, 9} chronic diseases,^{10, 11} disability,¹² and mental health.^{13, 14, 15} However, the relationship between immigration and health is complex. It involves both pre- and post-migration factors, for which information is often lacking. Hence, comparing the health of immigrants to that of the Canadian-born population is challenging.¹⁶

An additional factor is the increasing diversity in immigrants' origins. Since the 1960s, the major source countries have shifted from European to non-European nations. Consequently, it is important to analyze the healthy immigrant effect by world region and by period of immigration. However, small sample sizes have meant that most studies could not be conducted at this level of detail.

A comprehensive review of analyses of the relationship between immigration and health¹⁷ found that the relatively few studies of disease-specific mortality among immigrants compared with the Canadian population generally supported the healthy immigrant effect.^{18, 19, 20, 21, 22} More recently, all-cause mortality in immigrants was compared with that in the Canadian-born population.^{23, 24, 25, 26} Using unlinked 1991 mortality data, Trovato²³ found evidence of a healthy immigrant effect, but could not examine associations with period of immigration, immigration class, or socio-economic factors. DesMeules et al.²⁶ linked a random sample of 1980 to 1990 Citizenship and Immigration Canada landing files to 1980 to 1999 mortality data for all provinces and to health care data for Ontario, Quebec and British Columbia to study mortality risks by age, sex, region of birth, immigration category and time in Canada. The results generally supported the healthy immigrant effect and its eventual loss, notwithstanding some cause-specific exceptions. Though lacking in socio-economic data, that study contained detailed information about immigration (for example, immigration status, immigration class and period of immigration). It also found higher mortality rates among refugees than among other immigrants.

The present analysis used the 1991 to 2001 census mortality follow-up study to explore associations between mortality and dimensions of immigration such as country of birth and period of immigration. An earlier analysis of the same database by Wilkins et al.²⁶ showed a healthy immigrant effect, but the results pertained to the total immigrant population, with the sexes combined. The objectives of the present study were to determine:

1. if immigrants tend to have better health as measured by age-standardized mortality rates (ASMRs) than does the Canadian-born population (overall healthy immigrant effect);
2. if immigrants' initial health advantage lessens over time (duration effect); and
3. how results vary for immigrant subgroups, by world regions and selected countries at the Canada level and in Toronto, Montreal and Vancouver.

The analysis was conducted separately by sex for all causes combined and for circulatory diseases and cancer. To simplify the presentation, the disease-specific results are included in the appendix.

Findings

Descriptive results

The total 1991 to 2001 Canadian census mortality follow-up cohort numbered 2.7 million individuals who had been aged 25 or older in 1991; 552,300 or 20% were immigrants (Appendix Table B). Western Europe (comprising North, South and West Europe) was the top region of origin (close to 50%), followed by Eastern Europe (13%), the Caribbean/Central and South America (8%), and East Asia (8%). The majority (56%) were established immigrants who had arrived in Canada before 1971; 23% came between 1971 and 1981, and 21% were more recent immigrants who had arrived in the 1981-to-1991 period. The 1991 Census showed that those from Europe and the United States were most likely to be established immigrants, while those from Asia and Africa were more likely to be recent immigrants. For example, more than 70% of European immigrants had arrived before 1971, whereas the figure for immigrants from South Asia was 8%.

Figure 1 Age-standardized mortality rates (ASMRs) for immigrants, by sex and period of immigration, compared with Canadian-born cohort members, non-institutional population aged 25 or older at baseline, Canada, 1991 to 2001

In 1991, close to one immigrant adult in five (19%) was aged 65 or older, compared with 15% of Canadian-born adults. Moreover, the percentage of seniors varied by area of origin, reflecting periods of immigration; for example, 36% of Eastern European-born immigrants were seniors, compared with 5% of those who came from Sub-Saharan Africa.

In 1991, more than half (54%) of immigrants lived in Toronto, Montreal or Vancouver, whereas 25% of Canadian-born adults lived in these three cities. As well, the percentages varied by birthplace: 27% of those from the United States lived in these three CMAs, compared with 75% from East Asia.

Analytical results

Overall

For the adult population of Canada overall, the age-standardized mortality rates (ASMRs) per 100,000 person-years at risk were 1,230 for men and 703 for women (Figure 1). The immigrant population had significantly lower ASMRs than did Canadian-born adults: 1,006 versus 1,305 for men, and 610 versus 731 for women.

A rise in ASMRs as years in Canada increased reflects the loss of immigrants' health advantage over time. AMSRs among immigrant men were 720, 913 and 1,054 for the recent, medium-term and established cohorts, respectively. Among immigrant women, the corresponding rates were 491, 546 and 637. Even so, these rates were all significantly below those of the Canadian-born population.

A healthy immigrant effect was also evident for two major causes of death: circulatory diseases and cancer (Appendix Table C).

World region

ASMRs varied widely depending on the immigrants' birthplace (Table 1). Among men, ASMRs ranged from 668 (South Asia) to 1,112 (United States); among women, the range was from 439 (South East Asia) to 699 (United States). Despite these wide variations, the ASMRs of immigrants (especially men) from each world region were significantly lower than those of Canadian-born adults. The only exceptions were women from the United States and from Sub-Saharan Africa whose ASMRs were similar to that of Canadian-born women. For these groups, ASMRs were higher, regardless of period of immigration. For example, the ASMR among female immigrants from the United States who had arrived in the 1981-to-1991 period, was 739, compared with 731 for Canadian-born women.

Table 1 Deaths and crude and age-standardized mortality rates per 100,000 person-years at risk for immigrants, by sex, world region of birth and period of immigration, compared with Canadian-born cohort members, non-institutional population aged 25 or older at baseline, Canada, 1991 to 2001

The world regions exhibiting the effect of duration in Canada were:

• for both sexes – the Caribbean/Central and South America, Western Europe, Eastern Europe and East Asia;
• for men – North Africa/Middle East/West Asia and South Asia; and
• for women – South East Asia.

On the other hand, for some world regions, ASMRs were lower among established immigrants than among immigrants who arrived more recently. For instance, men who had immigrated from Sub-Saharan Africa before 1971 had a lower ASMR (825) than did Canadian-born men (1,305), while those who immigrated after 1980 had a higher ASMR (992).

Circulatory disease and cancer ASMRs generally support the overall healthy immigrant effect. However, ASMRs for circulatory disease among women from South Asia, Sub-Saharan Africa and the United States did not differ significantly from the figure for Canadian-born women (Appendix Table D). And women from the United States were the only group whose cancer ASMR was not significantly lower than that of Canadian-born women (Appendix Table E).

Census Metropolitan Area (CMA)

Overall, ASMRs in the three main destination Census Metropolitan Areas—Toronto, Montreal and Vancouver—support the healthy immigrant effect. For instance, the ASMR for immigrant men in Toronto was 974, significantly below the ASMR (1,280) for Canadian-born men in that CMA; the corresponding figures for women were 589 and 775 (Table 2).

ASMRs at the CMA level are strongly influenced by immigrants' place of birth. In 1991, at least 40% of the immigrants in each of the three CMAs were from Western Europe. Consequently, the overall immigrant ASMRs in these CMAs were closer to the levels experienced by Western European immigrants than, for example, to the levels among immigrants from Asia, who were less numerous.

The absence of a healthy immigrant effect among women from the United States and from Sub-Saharan Africa was apparent at the CMA level, although small numbers for the Sub-Saharan group limit the ability to detect an effect. As well, the healthy immigrant effect was not observed among men from the United States in these three CMAs. Nor was it observed among men from Sub-Saharan Africa in Vancouver. However, in Toronto, where close to half of Sub-Saharan African immigrants resided, their ASMRs were relatively low.

In the three CMAs, circulatory disease ASMRs among women from Sub-Saharan Africa and from South Asia did not differ significantly from those of Canadian-born women; and among women from the United States, this was the case not only for circulatory disease, but also for cancer (Appendix Table F and G). Moreover, some groups, while demonstrating an overall healthy immigrant effect, had elevated disease-specific ASMRs, especially when CMA-level data were examined. For example, women from Western and Eastern Europe and men from Eastern Europe living in Vancouver and men from the United States in all three CMAs had circulatory disease ASMRs that did not differ significantly from those of Canadian-born residents of these CMAS.

China, India and the United Kingdom

China (including Hong Kong) and India have been leading source countries since the 1980s; the United Kingdom had been a major source country in earlier years. A healthy immigrant effect was apparent among immigrants from each of these birthplaces (data not shown). Among men, at the national level, ASMRs were 690 for those from India, 810 for those from China, and 1,105 for those from the United Kingdom; this compared with 1,305 among Canadian-born men. Among women, the ASMRs were 537 (India), 471 (China), 695 (United Kingdom) and 731 (Canadian-born).

At the CMA level, ASMRs for immigrants from each of the three countries were generally lower than those for the Canadian-born (Table 3). The exceptions were women from India living in Toronto (634) and Montreal (503) and women from the United Kingdom in Vancouver (700), whose ASMRs did not differ significantly from those of Canadian-born women.

The elevated ASMR among women from India at the CMA level largely reflected a high circulatory disease ASMR (Appendix Table H). In Vancouver, the relatively high ASMR among women from the United Kingdom was partially due to high ASMRs for circulatory disease (289) and for cancer (281). Immigrants from China almost always had lower ASMRs, compared with those of the Canadian-born population in each CMA. However, in Montreal, the cancer ASMR among women from China (209) was similar to that of Canadian-born women (252).

Table 2 Deaths and crude and age-standardized mortality rates per 100,000 person-years at risk for immigrants, by sex and world region of birth, compared with Canadian-born cohort members, non-institutional population aged 25 or older at baseline, Toronto, Montreal and Vancouver, 1991 to 2001

Table 3 Deaths and crude and age-standardized mortality rates per 100,000 person-years at risk for immigrants from China (including Hong Kong), India or United Kingdom, by sex, compared with Canadian-born cohort members, non-institutional population aged 25 or older at baseline, Toronto, Montreal and Vancouver, 1991 to 2001

Discussion

The 1991 to 2001 census mortality follow-up study permits analysis of the healthy immigrant effect—the dominant hypothesis in immigrant health research—by world region of birth and for different areas of Canada. This hypothesis suggests that immigrants arrive with better health than the Canadian-born population, but that this health advantage tends to disappear over time. The results of this study provide overall support for this trend. However, similar to earlier research,^{24, 25} the analysis of ASMRs by world region of origin, period of immigration and residence reveals underlying differences that may not be evident when only the overall results are examined.

For example, the study found that female immigrants from South Asia tended to have high ASMRs for circulatory disease. This result confirms previous research that found high circulatory disease mortality rates among South Asians in Asian and non-Asian countries,²⁸ although results had been mixed for first-generation immigrants from these areas and resident in Canada. A study based on Canadian mortality data from the 1960s to the 1980s, which did not reveal an elevated risk for circulatory disease, reasoned that because of the immigration system's selection criteria pertaining to health status, South Asian immigrants might not be fully representative of the South Asian population in general.²² Nonetheless, a more recent study based on mortality data from 1979 to 1993 found high circulatory disease mortality among South Asians of both sexes in Canada.²⁰

Heterogeneity in ASMRs within immigrant subgroups living in Vancouver, Toronto and Montreal was also evident in this study. For example, men born in Eastern Europe and resident in Vancouver were found to have relatively high circulatory disease ASMRs, but their counterparts in Toronto and Montreal did not. This result highlights the importance of conducting country-specific and disease-specific research at the the CMA level.

Limitations

Overall, while this analysis provides support for the duration aspect of the healthy immigrant effect, the findings did not hold for immigrants from all world regions. Factors such as pre-migration socio-economic conditions and age at immigration may influence post-immigration mortality among the various cohorts. Also, immigration category (economic, family or refugee) may be an important determinant of post-immigration health outcomes; however, such data are not available from the 1991 to 2001 census mortality follow-up study.

This analysis has several other limitations. First, even with such a large database, sample size becomes a problem when world region of birth data are cross-classified by place of residence and period of immigration. As well, immigration patterns differ by CMA. For instance, Haitians tend to settle in Montreal; thus, studies of this group are likely to focus on only one CMA.

A second possible limitation is differential attrition in the census mortality follow-up study. If immigrants are more likely than the Canadian-born to move out of the country, it might partially explain the healthy immigrant effect that emerged in this analysis. However, while the possibility of immigrants moving out of the country exists, it is most common among younger people. Mortality rates at younger ages tend to be low, so such attrition should not have a noticeable impact on the results.

Third, the study is limited by the lack of information about risk factors, such as physical activity, body mass index, nutrition, smoking, and alcohol consumption. Such information is usually collected by health surveys which have small samples that restrict the ability to conduct country-specific analysis of the healthy immigrant effect.

Future directions

As the 1991 to 2001 census mortality follow-up study shows, even after 20 or more years in the country, immigrants from most world regions had lower ASMRs than did the Canadian-born population. Areas for further research include an examination of socio-economic determinants that may play a role in immigrant adaption and contribute to the healthy immigrant effect, including the initial medical assessments conducted at point of entry to Canada.²⁹ Further study of immigrants' mortality risk could involve the use of multivariate analysis to examine factors such as occupation, education and knowledge of official languages. As well, greater study of differences in the experience of various immigrant groups would be an important area of continued research. Future studies could also examine specific cancers (lung, colorectal, breast, etc.) and circulatory diseases (ischemic heart disease, cerebrovascular disease, etc.). Because this database contains other causes of death, analysis could also be conducted for causes such as diabetes and intentional and unintentional injuries.