Editorial commentary on ‘Country of birth and mortality risk in hypertension with and without diabetes: the Swedish Primary Care Cardiovascular Database’

The report by Andersson et al. [1], ‘Country of birth and mortality risk in hypertension with and without Diabetes: the Swedish Primary Care Cardiovascular Database’, represents a novel approach to assessing nativity and mortality. Most reports and systematic reviews of nativity and health document that international immigrants have better outcomes for multiple health indicators than native born individuals [2]. Rather than analyzing an overall population sample, the current report focused on total mortality as well as the incidence of myocardial infarction and stroke among immigrants and Swedish natives with hypertension in primary care settings from 1996 through 2012. Outcomes were also assessed among adults with hypertension who did and did not develop diabetes mellitus after the diagnosis of hypertension. The heterogeneity in total noncommunicable disease, coronary heart disease and stroke mortality among high-income and low-income European Union (EU) countries and Nordic countries is substantial (Table 1). The variable health outcomes between countries from which immigrants originate suggest that country of origin is at least as important as region and income in assessing whether the differential mortality reflects the overall health of citizens in countries from which immigrants originated or whether immigrants are healthier than those who remained in their native country. TABLE 1 - Per capita income (2012) and coronary heart disease and stroke deaths in EU27 Countries (UK added) High-income European Union countries Low-income European Union countries EU27 country GDP/capita NCD death CHD death Stroke death EU27 country GDP/capita NCD death CHD death Stroke death Luxembourg 92 102 247.7 49.0 19.7 Cyprus 39 079 306.0 78.7 27.8 Germany 53 571 295.9 73.5 22.2 Lithuania 38 605 390.9 199.8 73.0 Belgium 50 114 270.7 47.3 22.0 Slovenia 38 506 274.6 69.9 35.5 Finland 49 334 274.8 68.9 27.3 Spain 38 143 225.7 38.9 19.4 Netherlands 46 491 295.1 42.9 22.9 Estonia 37 033 335.1 161.6 29.7 Ireland 46 058 299.7 60.6 21.3 Poland 33 739 347.2 144.9 41.7 Austria 45 466 272.2 75.7 18.8 Portugal 33 131 245.0 38.4 38.3 France 45 454 222.7 31.0 16.6 Hungary 32 434 444.6 181.8 48.7 United Kingdom 44 288 295.1 47.6 21.6 Slovakia 32 184 367.9 133.7 46.6 Sweden 44 057 273.4 58.3 21.6 Latvia 30 579 413.4 175.9 92.8 Denmark 43 933 300.6 38.6 23.9 Romania 30 141 442.6 179.4 94.4 Malta 43 087 287.5 92.8 29.2 Greece 29 045 265.0 71.2 41.6 Czechia 40 293 331.3 124.8 35.6 Croatia 27 681 358.6 115.8 59.0 Italy 40 066 250.2 51.3 26.8 Bulgaria 23 741 483.8 215.3 121.4 Non-European Union Nordic countries Norway 64 699 261.9 46.6 20.9 Iceland 41 005 283.6 62.6 20.0 Bold death numbers higher than Sweden. Italicized death numbers lower than Sweden. European Union countries (UK added) are listed in order of decreasing per capita income for calendar year 2012. CHD, coronary heart disease; EU, European Union; GDP, Gross Domestic Product; NCD, noncommunicable disease. Data sources: https://en.wikipedia.org/wiki/List_of_sovereign_states_in_Europe_by_GDP_(PPP)_per_capita; https://www.who.int/data/gho/data/indicators/indicator-details/GHO/gho-ghe-ncd-mortality-rate; https://www.worldlifeexpectancy.com/cause-of-death/coronary-heart-disease/by-country/; https://www.worldlifeexpectancy.com/cause-of-death/stroke/by-country/. After adjusting for clinical and sociodemographic characteristics, immigrants from Finland experienced higher rates of total mortality, whereas immigrants from high-income and low-income European countries and non-European countries had lower rates of total mortality, and immigrants from Nordic countries other than Finland had similar mortality rates relative to Swedish natives. The findings on total mortality were obtained in the total cohort group of patients with hypertension and the subset that did not develop diabetes during the observation period. Among adults with hypertension who developed diabetes, total mortality was lower among immigrants from Finland, high-income and low-income European and non-European countries. Adults with hypertension who developed diabetes had higher mortality rates than those without the comorbid condition. The excess mortality risk of diabetes persisted with adjustment for clinical and sociodemographic characteristics, conferring an approximately 50% excess risk regardless of nativity. The focus on immigrants with hypertension as compared with the overall immigrant pool is novel and important. More specifically, hypertension is a chronic condition frequently associated with multiple comorbid conditions and less favorable health outcomes, including greater total and cardiovascular mortality [3]. Moreover, baseline comorbidities including ischemic heart disease, atrial fibrillation, heart failure, cerebrovascular disease and renal failure were generally comparable in Swedish born and foreign immigrants [1]. The non-European immigrants had lower rates for most comorbid conditions than Swedish natives and other immigrants but they were also 8–11 years younger than the other groups. In this regard, it is important to note that the significant findings in Cox proportional hazards regression included adjustment for multiple measured confounders. Covariates included age, sex, calendar year of study, income, education, time-updated diabetes status, baseline preexisting cardiovascular conditions, renal failure, cancer, SBI and DBP after the diagnosis of hypertension, serum lipids and lipoproteins and BMI. The healthy immigrant effect is well documented. Immigrants to Europe, Canada, Australia and the United States generally have better health and longevity than natives [2]. Analysis by race/ethnicity and region of origin sometimes reveal striking differences along the lines of the current report in which Finnish immigrants are marked by higher mortality rates, whereas European and non-European immigrants had lower rates. In the United States, male and female immigrants live 3.4 and 2.5 years longer, respectively than US-born individuals [4]. However, there is substantial heterogeneity as black male and female immigrants to the United States have 9.4 and 7.8 years greater longevity, respectively, than US-born blacks. In fact, black immigrants to the United States have a lifespan ∼2 years greater than the mean for the US-born population, whereas the US-born black population has 5--7 years’ shorter lifespan. Despite socioeconomic disadvantages, non-Hispanic black immigrants have better self-rated health than non-Hispanic white immigrants to the United States [5]. Of interest, non-Hispanic blacks in the United States experience a high incidence of low birthweight infants, which is not seen among black immigrants, which would confer health advantages to the second generation of this immigrant population [6,7]. In contrast to the longer lives of black immigrants than US-born blacks, Asians born in the United States have a longer lifespan than Asian immigrants [4]. US-born Asians have less cancer and communicable disease, which contributes to their longevity advantage, despite more cardiovascular risk and disease [7]. Factors underlying the healthy immigrant effect vary between studies, and are not fully understood. The better health of immigrants than natives partially reflects immigration policies that select individuals for better health [2,8]. The healthy immigrant effect in the United States is significantly attenuated when immigrants are compared with natives who move within the country for job-related reasons, which is a primary motivation for most immigrants [9]. In other words, the healthy immigrant effect may partially represent a healthy mover effect. Along this line, the healthy immigrant effect in the United States is reduced when the primary reason for immigration is family-related rather than work-related [10]. Study design is another important consideration in assessing the healthy immigrant effect. Many studies of immigrant health are based on repeated cross-sectional assessments of immigrant cohorts, which raises at least three issues [11,12]. One key consideration is whether the cohort arrived in a wave or in a relatively continuous fashion. This first consideration assumes greater importance if host country residence leads to adverse, time-dependent health changes, which is a second variable to consider. A third variable is the impact of remigration to the country of origin before the cohort is selected for evaluation. In fact, a longitudinal study from the United States did not observe a decline in the health of Asian or Latin American immigrants with time in contrast to cohort studies [12]. However, the longitudinal study may have been of insufficient duration to capture adverse effects of United States residence on immigrant health, which are documented over 10--20 years [13]. Refugee status can impact the magnitude of psychological distress. Among immigrants to Sweden, refugees generally had higher levels of psychological distress than nonrefugees [14]. The investigators noted that social capital was an important mediator of the relationship of psychological distress among immigrants and advocated for policies that promote social capital. In summary, the report by Andersson et al.[1] documents differential mortality of immigrants to Sweden among adults with hypertension receiving primary care. Mortality advantages are seen for immigrants with hypertension from non-Nordic countries. This finding aligns with the general health advantages of immigrants to Australia, Canada, Europe and the United States over residents born in those countries [2]. Yet, many reports indicate health advantages of immigrants dissipate with time. These observation support recommendations that at least as much attention should be directed to maintaining immigrant health over time as to insuring that immigrants are healthy upon arrival [15]. The current report would extend that guidance to immigrants with hypertension. ACKNOWLEDGEMENTS Disclaimer: The comments and conclusions in this paper are those of the authors and do not necessarily represent the views of the American Medical Association. Conflicts of interest There are no conflicts of interest.

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