This systematic review and meta-analysis quantified the differences in risk of T2D complications in ethnic minority populations residing in Europe, compared with their host populations. The results revealed diverse patterns of risk for T2D complications across ethnic groups. Noteworthy is the consistent lower risk of all-cause mortality among ethnic minority compared with European host populations, primarily driven by reduced CVD and cancer mortality. We found a general trend of lower risks for macrovascular complications, but not for South Asian populations. Our study also suggests higher risks of both nephropathy and retinopathy among specific ethnic subgroups compared with European host populations. No differences between ethnic minority and European host populations were observed for mental disorders.

Our study showed that the risk of all-cause mortality is nearly one-and-a-half times lower among ethnic minority compared with European host populations. This contrasts with the meta-analysis by Ezzatvar et al, which identified a two-fold higher all-cause mortality risk for Māori, compared with White host populations, and no differences in all-cause mortality risks for any other ethnic groups.10 It is important to note that the study by Ezzatvar et al10 included only one study from Europe, while all other included studies were conducted in North America and New Zealand. Moreover, only one of the ethnic minority populations overlapped with those in our study (Sub-Saharan African/black). Contextual factors vary considerably between continents, contributing to the observed differences in direction of the association. In particular, there are larger inequalities in care in the USA than in Europe.21 Most studies included in our meta-analysis were conducted in the UK or the Netherlands, where access to basic healthcare services is common. Examining cause-specific mortality further delineates that the lower risk of all-cause mortality among ethnic minorities compared with European host populations may be driven by the lower risks of cancer and CVD.19 22–24

Risk of macrovascular complications was lower among most ethnic minority populations compared with host populations. South Asians, however, showed comparable risks for most macrovascular complications and slightly higher risk of MACE. Moreover, cross-sectional studies suggested an almost twofold higher risk of CHD among South Asians compared with host populations, aligning with the high risk for both T2D and CVD described in the literature.5 25 This may partly be explained by the high susceptibility to central obesity among South Asians.26 Explanations for the lower risk of all-cause mortality and macrovascular disease among ethnic minorities compared with European host populations may be multifactorial, involving genetics, biological responses to medication and behavioral attitudes. First, Wright et al suggested that the prevalence of risk factors such as smoking, hypertension and obesity may be lower, while the exposure to glucose-lowering medication may be higher among ethnic minority compared with European host populations.19 This aligns with observations of Mathur et al, who reported better or equivalent cardiometabolic profiles among ethnic minority compared with European host populations at the time of diagnosis, along with a shorter time until initiation of antidiabetic treatment.27 Second, it is plausible that physicians, aware of the increased T2D risk in ethnic minority populations, initiate treatment early in the course of T2D among ethnic minority but not among host populations. Our study did not assess whether ethnic groups received similar quality of care. Lower risks may for instance stem from heightened awareness among both ethnic minority populations and their physicians regarding the elevated T2D risk prevalent from a young age within these communities.5 Some studies suggest temporal changes in ethnic differences in T2D risk, since a study in 1996 reported two to four times higher all-cause mortality risks among ethnic minority populations compared with individuals born in the UK.28 We did not find indications of such a trend, and excluded this study because of an inappropriate study design, as it used death certificates to establish T2D diagnosis. Importantly, variations in risk of macrovascular complications were evident across subgroups and type of complications. Sub-Saharan Africans consistently had reduced risks, supporting the notion of a lower cardiovascular burden among this group, due to better cardiometabolic profiles.27 29

Our analysis revealed no overall differences in microvascular complications across ethnic groups. However, closer examination showed elevated risks for retinopathy and nephropathy among ethnic minority compared with European host populations, ranging from slightly higher to one-and-a-half times higher risks. These studies mainly included people of South Asian and Sub-Saharan African ethnicity. Future studies should examine whether these observations are consistent in other ethnic minority populations. Limited evidence for neuropathy was found, necessitating more high-quality studies. Yet, some studies suggest higher risks of painful diabetic neuropathy among South Asians.20 Higher risks for nephropathy may be attributed to a higher prevalence of comorbidities, including hypertension (mainly among Sub-Saharan African populations), metabolic syndrome and chronic hepatitis B infections, as people with these comorbidities may have a more rapid decline of kidney function than people with T2D alone.30–33 The increased risk of nephropathy and retinopathy may also be influenced by factors such as the stage of T2D progression at diagnosis and healthcare system disparities. Discrepancies in monitoring and prescriptions were reported for Sub-Saharan African and Asian compared with European individuals, although studies show conflicting results.27 34 Despite these conflicting reports, ethnic minority populations in Europe generally exhibit lower glycemic control,35 36 which may explain an increased risk of microvascular complications.37 Our analysis did not find statistically significant differences in the prevalence of depression among ethnic minority, compared with European host populations. Importantly, methodological variations in assessing depression may affect study outcomes. Although not statistically significant, a lower prevalence of depression among South Asians compared with the European host population was observed with the WHO-5 model, but opposite findings were reported with the Center for Epidemiologic Studies Depression scale (CES-D), due to low agreement between both scales.38

This study has several limitations. First, the observed high heterogeneity may stem from variations in study designs, methodologies and unmeasured confounding factors. Despite attempts to account for heterogeneity through sensitivity analyses, residual heterogeneity may still exist due to unmeasured confounding factors or differences in populations characteristics. Nonetheless, the directionality of the key findings was consistent across the subgroups, and the high heterogeneity is thus unlikely to affect our conclusions. Second, ethnic minority populations were categorized based on geographical origin, following the IDF classifications. While this approach provides a broad overview, it may oversimplify the complex diversity within ethnic minority populations. Subgroups within these broad categories may have distinct risk profiles and healthcare needs that were not captured in the analysis. Yet, data of all individual studies is made visible, with the original categories as described in the original paper displayed, which provides the opportunity to further assess the granularity within IDF regions. Third, although subgroup analyses by sex were planned, the scarcity of studies reporting findings stratified by sex withheld us from these analyses. Finally, the variation in countries where the studies were conducted, predominantly in the UK, was limited which impedes a comprehensive assessment of potential differences by host country. Additionally, most studies focused on South Asian and/or Sub-Saharan African populations, which limits our ability to draw firm conclusions regarding other ethnic groups that were less frequently studied.

In summary, ethnic minority populations in Europe are generally at reduced risk of all-cause mortality and macrovascular complications, but might be at higher risk of microvascular complications. However, heterogeneity is evident, both in the type of complication and across ethnicities. Where most ethnic minority populations are at reduced risk of macrovascular complications and MACE, South Asians have comparable risks of most macrovascular complications and a slightly higher risk of MACE. The lower risks of adverse health outcomes among ethnic minority populations do not negate the importance of healthcare professionals remaining vigilant to potential differences in risk of T2D complications and healthcare disparities. Future studies may for instance investigate how healthcare professionals differentiate in the care provided to various ethnic groups and how this relates to the development of T2D complications.