The healthy immigrant effect and mortality rates

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by Edward Ng

In 2006, immigrants made up one-fifth (19.8%) of Canada's population, a percentage that is expected to reach at least 25% by 2031.1 The health and the health services needs of this large and growing share of the population are not necessarily the same as those of people born in Canada.2,3 Research has repeatedly found a "healthy immigrant effect"—immigrants' health is generally better than that of the Canadian-born, although it tends to decline as their years in Canada increase.4-14 However, the relationship between immigration and health is complex, especially because the origins of immigrants to Canada are increasingly diverse. 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 birthplace and period of immigration.

The present analysis used the 1991 to 2001 Canadian census mortality follow-up study to explore associations between mortality and birthplace and period of immigration (see The data). The objectives were to determine:

if immigrants have better health, as measured by age-standardized mortality rates (ASMRs) than does the Canadian-born population (overall healthy immigrant effect); if immigrants' initial health advantage lessens over time (duration effect); and if the results hold for immigrant subgroups, by birthplace and by selected country at the national level and for the three largest Census Metropolitan Areas (CMAs)—Toronto, Montreal and Vancouver (where possible).

The adult immigrant population

The total 1991 to 2001 Canadian census mortality follow-up cohort numbered 2.7 million individuals who were aged 25 or older in 1991; 552,300, or 20% of them, were immigrants. Close to 50% of these immigrants were born in Western Europe (comprising North, South and West Europe), followed by Eastern Europe (13%), the Caribbean/Central and South America (8%), and East Asia (8%). The majority (56%) were established immigrants who arrived in Canada before 1971; 23% arrived between 1971 and 1981; and 21% were more recent immigrants who arrived in the 1981-to-1991 period. Immigrants from Europe and the United States were more likely to be "established," while those from Asia and Africa were more likely to be "recent." For example, 80% of immigrants from Western Europe arrived before 1971, whereas the figure for immigrants from South Asia was 8%.

In this study, close to one in five immigrant adults (19%) was aged 65 or older, compared with 15% of Canadian-born adults. The higher percentage of seniors among immigrants reflected the higher percentage who had been born in Europe and the United States and is indicative of the diverse waves of immigration and settlement patterns that have occurred in Canada. For instance, 36% of immigrants in the study from Eastern Europe were seniors, compared with 5% of those from Sub-Saharan Africa and Western Asia.

More than half (54%) of immigrant adults lived in Toronto, Montreal or Vancouver. The percentage varied from 28% of those from the United States to 73% of those from the Caribbean/Central and South America. By comparison, 25% of Canadian-born adults lived in these three cities.

Healthy immigrant effect: Lower mortality rates

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

Table 1 Age-standardized mortality rates, by sex, birthplace and period of immigration, non-institutional cohort members aged 25 or older at baseline, Canada, 1991 to 2001

However, as immigrants' time in Canada lengthened, their ASMRs tended to rise. It is hypothesized that this upward trend in ASMRs reflects a loss of immigrants' health advantage over time. The AMSRs among men were 720, 913 and 1,054 for recent, medium-term and established immigrants, respectively. Among immigrant women, the corresponding rates were 491, 546 and 637. Nonetheless, these rates remained significantly lower than those of the Canadian-born population.

Birthplace matters

ASMRs varied widely depending on where immigrants had been born (Table 1). Among men, ASMRs ranged from 668 (South Asia) to 1,112 (United States); among women, the range was from 439 (Southeast Asia) to 699 (United States). Despite these wide variations, the ASMRs of immigrants were generally 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.

The study results indicate that ASMRs for immigrants from most regions of the world increased with time in Canada (duration effect):

among both sexes – from the Caribbean/Central and South America; Western Europe; Eastern Europe; East Asia.

among men only – North Africa/Middle East/West Asia; South Asia.

among women only – South East Asia.

However, the rise in ASMRs with duration of residence in Canada did not occur in all cases. For example, men who came to Canada from Sub-Saharan Africa before 1971 had a lower ASMR (825) than did those who arrived in the 1981-to-1991 period (992).

Toronto, Montreal and Vancouver

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

Table 2 Age-standardized mortality rates, by sex and birthplace, non-institutional cohort members aged 25 or older at baseline, Toronto, Montreal, Vancouver, 1991 to 2001

ASMRs at the CMA level are heavily influenced by immigrants' birthplace and period of immigration. At least 40% of the immigrants in each of Toronto, Montreal and Vancouver came from Western Europe and had been in Canada for more than ten years. As a result, while ASMRs were lower compared with the Candian-born, overall ASMRs were closer to the levels for Western European immigrants who made up a larger percentage of the population in the study, compared with immigrants from Asia, whose ASMRs tended to be lower, but who made up a smaller percentage of the overall CMA immigrant population at that time.

For women in the three CMAs who had been born in the United States or in Sub-Saharan African countries, ASMRs were closer to those of Canadian-born women living in these locations. As well, the healthy immigrant effect was less evident among men from the United States living in these three CMAs —their ASMRs more closely resembled those of the Canadian-born than those of other immigrant groups. By contrast, for the Sub-Saharan African group, in Toronto, where close to half of them lived, ASMRs of male immigrants compared favourably with those of other immigrant groups.

China, India and the United Kingdom

In the 1991-to-2001 census mortality follow-up study, China (including Hong Kong) and India were leading source countries of recent immigrants to Canada, whereas the United Kingdom had been a major source in the past.

Overall, a healthy immigrant effect was apparent among immigrants from each of these countries. The ASMRs among men 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 for Canadian-born men (data not shown). Among women, the ASMRs were 537 (India), 471 (China), 695 (United Kingdom) and 731 (Canadian-born).

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

Table 3 Age-standardized mortality rates, for immigrants from China, India or United Kingdom, by sex, non-institutional cohort members aged 25 or older at baseline, Toronto, Montreal, Vancouver, 1991 to 2001

When cause of death is examined, the elevated ASMR among women from India at the CMA level reflects higher circulatory disease ASMRs (data not shown).16 Similarly, in Vancouver, the higher ASMR among women from the United Kingdom was partially due to circulatory disease and cancer.16 Immigrants from China typically had low ASMRs , but in Montreal, the cancer ASMR among women from China was comparable to that of Canadian-born women.16

Conclusion

The results of this study indicate an overall healthy immigrant effect that diminishes with years since immigration to Canada. Moreover, even after 20 or more years in the country, immigrants' ASMRs were generally lower than those of the Canadian-born population.

However, the analysis of ASMRs by birthplace, period of immigration and area of residence in Canada reveals the heterogeneity between and within immigrant subgroups and highlights the importance of country-specific research at the CMA level.

As the percentage of the population made up of immigrants continues to grow, interest in their health status will increase. As a result, the need for in-depth analysis based on surveys with larger samples of immigrants and on linked data such as the Canadian census mortality follow-up study will also increase.

Acknowledgements

Major funding for the Canadian census mortality follow-up study was provided by the Canadian Population Health Initiative, part of the Canadian Institute for Health Information. The importance of Canada's provincial and territorial registrars of vital statistics, who provide the death data for the Canadian Mortality Data Base is also acknowledged.