Type II diabetes is more common in ethnic minority groups than in the European white populations.1–3 Unhealthy behavior following migration, obesity and adiposity, and early life exposures such as low birth weight, low socioeconomic position, genetic predisposition, and psychosocial stress have all been suggested as possible underlying factors.4–6
Although the risk of diabetes is comparatively high in most ethnic minority groups, the magnitude of the risk may vary between countries due to differences in national contexts. Ethnic minority groups living in industrialized countries with more diabetogenic environments may be more prone to diabetes than those living in countries with less diabetogenic environments. Recent diabetes prevalence estimates suggest marked differences among countries. For example, the age-standardized prevalence of diabetes in 2007 was 7.3% in the Netherlands compared with 4.0% in the United Kingdom.7 These findings are consistent with data from the Organisation for Economic Co-operation and Development, which show that Dutch people die more often from diabetes-related complications than their British counterparts.8 The reasons for these differences are unclear, but may relate, at least in part, to differences in national context in terms of health behavior and related factors such as obesity and adiposity, and differences in the health-related policy such as screening program. These differences may also affect ethnic minorities living in these countries. In addition, socioeconomic position, accessibility, and utilization of preventive services in the residing countries may also differ, and subsequently affect ethnic minority health outcomes in different ways.9,10
Although recent evidence7 shows clear differences in the overall prevalence of diabetes among European countries, it is unclear as to whether these differences are also seen among ethnic minority groups living in these countries. The aim of this study was therefore to examine ethnic differences in the prevalence of diabetes in 2 European countries, and to determine whether the lower prevalence of diabetes in the United Kingdom as compared with the Netherlands is also observed in the Indian and African-Caribbean populations living in these 2 countries. In addition, we assessed the contribution of physical activity, smoking, body sizes, and socioeconomic position to the observed differences between countries.
We hypothesized that the prevalence of diabetes would be higher in Dutch minorities than their English equivalents, as a reflection of the English and Dutch difference among whites, due to exposure to different national contexts. These differential exposures may affect ethnic minorities' health behavior and related factors in different ways, and subsequently lead to differences in the risk of developing diabetes (Fig. 1).
This study is a part of a project to develop approaches to cross-national comparisons as a basis for future multinational comparisons.9,11,12 The definition of ethnic groups and brief histories of migration have been given elsewhere.11,12
We used data from population-based surveys that collected standardized data on cardiovascular disease and risk factors in populations of Indian and African-Caribbean origin in England and the Netherlands. All studies were population-based health surveys with data on ethnic minority and white populations. Each collaborator agreed to provide anonymized individual participants' data on risk factors, anthropometry, lifestyle, socioeconomic position, and demographics. The UK data were obtained from the Health Survey for England13 and the Newcastle Heart Project.14 The data on the Dutch ethnic groups came from the SUNSET Study.2 Full details of the studies have been published elsewhere.2,13,14 The short descriptions of the studies and measurements are given in eAppendix 1 (http://links.lww.com/EDE/A485).
Diabetes prevalence rates were age-standardized using direct standardization for both sexes, with the standards being the age distribution of the total population. Prevalence rate ratios (PRs) of diabetes and their 95% confidence intervals (CIs) were estimated by means of Poisson regression with robust variance15 and adjusted for available individual factors associated with diabetes: physical activity, smoking, body sizes, and socioeconomic position.4–6 In addition, we adjusted all the analyses for year of survey because the time frame over which the studies were performed varied both within and between studies. All analyses were performed using STATA 9.2 (Stata Corp, College Station, TX).
Table 1 shows differences in the study characteristics between Dutch and English groups. Ethnic inequalities in diabetes were relatively similar in both countries. Among the English group, men and women of Indian origin had a higher prevalence of diabetes than their English white counterparts (Fig. 2). The differences did not change after further adjustment for other factors in both men and women (Table 2). English-African-Caribbean men and women also had a higher prevalence of diabetes than their English white counterparts (Fig. 2). After adjustment for other factors, the PRs were 1.97 (95% CI = 0.82 to 4.74) in men and 1.90 (0.78 to 4.65) in women. Among the Dutch group, both Indian-origin and African-origin men and women had higher prevalence rates of diabetes than their Dutch White counterparts.
Among whites, English men and women had lower prevalence rates of diabetes than their Dutch counterparts (Fig. 2). The PRs were 0.45 (0.24 to 0.84) in men and 0.45 (0.18 to 1.15) in women after other factors had been adjusted for (Table 3). Indian men and women residing in England also had lower prevalence rates of diabetes than their Dutch counterparts. After further adjustment for other factors, the PRs were 0.35 (0.22 to 0.55) in English-Indian women and 0.74 (0.50 to 1.10) in English-Indian men. Women of African-Caribbean origin in England also had a lower prevalence rate of diabetes than those in the Netherlands (PR was 0.43 [0.20 to 0.89]); for men, the PR was 0.57 (0.21 to 1.49).
Similar differences were also observed when fasting glucose was analyzed as a continuous variable (data not shown).
A few studies have compared prevalence of diabetes among African or Indian populations living in industrialized countries with people who remained in their countries of origin.16–18 The high prevalence of diabetes among ethnic minority populations living in industrialized countries had been largely attributed to transition to an industrialized lifestyle following migration, which is associated with most known risk factors.16,17 Studies examining ethnic minority populations living in different industrialized countries are, however, limited in number.19 In the present study, substantial variations still exist with Indian and African ethnic minorities in the Netherlands having higher diabetes rates than their English equivalent groups.
The reasons for these marked differences are unclear. Unmeasured factors such as diet and early life experiences, as well as unmeasured aspects of physical activity and socioeconomic position (eg, occupational class and income), may contribute. It is also possible that the relatively high prevalence of diabetes among Dutch ethnic minority groups may be related to the context in which they live. First, possible specific risk factors might be embedded in national policies and related national conditions. Exposure to lifestyle-related risk factors may be influenced by food production and marketing, urban design, health education, and transport; and these may differ between England and the Netherlands. Second, local traditions regarding food, as well as food policy, may also have an influence on ethnic minority diets.20 The rate at which dietary change occurs after immigration may largely depend on the national context; the availability of familiar foods and the migrant's level of contact with compatriots and their country of origin, or with the white populations, may all play a part. Third, diabetes guidelines and adherence to diabetes prevention advice such as smoking cessation varies widely between the 2 countries.10,21,22 The UK diabetes guideline, for example, has been shown to give more attention to ethnic minorities than does the Dutch diabetes guideline.10 Evidence from England also suggests that ethnic minority smokers attempt to quit as often as nonminority smokers.21 The Dutch data, by contrast, suggest that the majority of the Dutch-Indian and Dutch-African smokers were not motivated to quit smoking.22
There are limitations to this study. Data collection instruments in the 2 studies were designed independently. Differences in study methods might have introduced bias in the prevalence estimates. Nevertheless, all the studies used standardized methods and validated instruments, and the prevalence rates were consistent with other data.7 Additionally, we did not have data on all the important explanatory variables that might contribute to the observed differences, such as diet, psychosocial stress, and early-life exposures. Furthermore, we lacked valid data on other types of physical activity and socioeconomic position measures.
Despite these limitations, the analysis provides useful information on Dutch and English-Indian and African-Caribbean populations. The findings suggest that the increasing prevalence of diabetes following migration may be modified by improving the context in which ethnic minority groups live. Further studies could explore the role of national context, also taking into account unmeasured or mismeasured factors. Analysis of international datasets on diabetes and cardiovascular disease in multiethnic populations constitutes a potentially important strategy.9,19 The success of this approach requires cross-standardization of studies across countries.
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