Immigration presents a potential increased risk for atherosclerosis
Introduction
Immigrants comprise an increasing proportion of the population of Western countries as these countries actively seek to maintain economic productivity with the anticipation that immigrants will fill key labour niches. In these countries, the growth of the immigrant population has outpaced that of the native born population. In Canada, the United States (US) and the United Kingdom, the immigrant population has increased by 2.5, 4.4 and 7.8 times that of the general population, [1], [2], [3]. The net migration tends to be from countries with a low prevalence of cardiovascular disease (CVD) to countries in which CVD is one of the leading causes of death [4], [5].
Moving from a country with a low CVD risk to a country of higher CVD risk may result in an increase in CVD as indicated by Japanese immigrants living in the US having a higher prevalence of CVD than a similar population living in Japan [6]. Since then, other studies have reported that the prevalence of CVD risk factors is higher in immigrants in their new country than individuals living in their home country [7], [8]. Additional investigations have indicated that time since immigration influences risk factors in immigrant populations [9], [10], [11], and over time, immigrant risk factors may surpass that of the non-immigrant population [12]. Time since immigration was also associated with greater coronary calcification in a multi ethnic cohort living in the US [13]. Similarly, duration of residence in the US was an independent predictor of self-reported CVD in South Asians [14]. This may result in increased CVD mortality as observed in immigrant women living in the US but not in immigrant men [15]. However, these studies are few in number and are limited in several ways: investigation of specific ethnic groups [10], [13], [14], use of self-reported measures [7], [9], [11], [14], investigation of risk factors and not disease [7], [9], [10], [11], [12], [8], and lack of comparison to a non-immigrant group [7], [9], [14].
While immigration to Western countries appears to be associated with increased risk for CVD, it is unclear if this risk is greater than that of non-immigrants in the same country, or if this increased risk in immigrants is the result of acclimatization to the risk and prevalence of CVD of their new country. We suspect that immigrants are at greater risk than non-immigrants and therefore, the increased risk in immigrants is not due to acclimatization of their new country's risk for CVD. Using data from the Multi-cultural Community Health Assessment Trial (M-CHAT), we hypothesized that time since immigration is an independent predictor of sub-clinical atherosclerosis in immigrants of European, Chinese and South Asian origin, and as time since immigration increases, immigrants will actually be at greater risk than non-immigrants. With the world's largest populations originating in Asia and the increasing proportion these groups contribute to immigration to Western countries [1], [2], [3], understanding the health risks/benefits associated with immigration per se are important to identify and help guide targeted interventions.
Section snippets
Methods
Study participants were taken from the M-CHAT study [16]. Healthy men and women with all known ancestors of either Chinese, European or South Asian origin were eligible if they lived in Canada for more than three years and were less than fourth generation. Individuals were excluded if they had undergone recent weight change (≥2.2 kg in three months), reported a previous diagnosis of CVD or significant co-morbidity (HIV, immunocompromised conditions and type 1 diabetes), were taking medications
Results
Of the 618 men and women of Chinese (n = 216), European (n = 197) and South Asian (n = 205) origin included in the analysis, 158 (26%) were non-immigrants. Non-immigrants tended to be predominantly of European origin (72% vs. 18%, p < 0.001), had a higher level of education (72% vs. 52% for post-secondary education, p < 0.001) and income (61% vs. 33% for annual household income >$60000, p < 0.001), and higher self-reported health status (81 (14) vs. 78 (16), p = 0.030) compared to immigrants. There was no
Discussion
Our results indicate that while immigrants as a whole had a lower burden of sub-clinical atherosclerosis than non-immigrants, as time since immigration increased so did IMT and therefore potential risk for CVD. Of note, was that participants who immigrated >20 years prior, had greater IMT than non-immigrants irrespective of age, ethnicity and socio-economic status. Time since immigration was positively associated with IMT independent of age, ethnicity, socio-demographics, lifestyle and risk
Conclusions
This study provides novel findings indicating that time since immigration is a potential risk factor for the development of sub-clinical atherosclerosis and therefore CVD. Those participants who had the greatest time since immigration had greater carotid atherosclerotic burden than non-immigrants. This occurred regardless of age and ethnic background, suggesting that immigration itself may pose a unique risk for CVD. Of particular note was that time since immigration was the fourth strongest
Acknowledgements
Sources of funding: This research was funded by the Canadian Institutes of Health Research: Institute of Nutrition, Metabolism and Diabetes. Dr. Lear is a Canadian Institutes of Health Research New Investigator and Dr. Humphries is a Canadian Institutes of Health Research New Investigator and Michael Smith Foundation Career Investigator. The authors had complete independence from the funders.
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