A systematic review of 573,173 individuals with type 2 diabetes found South Asian, Black, and Chinese ethnic groups have significantly lower all-cause mortality risks compared to White populations, while Māori and Indigenous Australians face higher mortality.
Study: Comparison of mortality in people with type 2 diabetes between different ethnic groups: Systematic review and meta-analysis of longitudinal studies. Image Credit: PhotoGullak / Shutterstock
In a recent study published in the journal PLoS ONE, researchers in the United Kingdom compared all-cause mortality risk among individuals with type 2 diabetes (T2D) across different ethnic groups through a systematic review and meta-analysis.
Background
T2D is a major global health concern, nearly doubling mortality risk compared to those without diabetes, primarily due to circulatory diseases, but increasingly cancer and neurodegenerative conditions.
Ethnicity is a significant risk factor, with South Asian and Black populations experiencing higher prevalence, earlier onset, and differing complication profiles compared to White populations. While advancements in T2D management have reduced vascular-related mortality, ethnic disparities in outcomes remain underexplored, and broad ethnic categories used in studies may mask important subgroup differences.
Further research is needed to explore factors driving these differences and to guide targeted interventions for improving outcomes in T2D management across diverse populations.
About the study
The present systematic review was conducted following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. The protocol was registered in the international Prospective Register of Systematic Reviews (PROSPERO). Articles were searched across nine databases, including Ovid Medline, Embase, PsycInfo, Global Health, and others, in March 2023, with updates in May 2024.
The search strategy employed a combination of controlled vocabulary (Medical Subject Headings [MeSH]) and keyword searching, using Boolean operators. Searches were finalized through group consensus for terms related to T2D, ethnicity, and longitudinal cohort studies, excluding studies with data collection or follow-up before 2000.
Eligible studies included adults aged 18 years or older with T2D from population-based settings. Studies had to compare at least two ethnic groups, with no restrictions on location, language, or health status. Exclusion criteria focused on studies of children, type 1 diabetes, gestational diabetes, or populations selected based on specific comorbidities. Longitudinal cohort studies and secondary analyses of randomized controlled trials (RCTs) were included, while other designs, such as case series or cross-sectional studies, were excluded.
Study quality was assessed using the Newcastle-Ottawa Scale (NOS), and data analysis included meta-analysis for studies reporting hazard ratios (HRs) for all-cause mortality. Statistical heterogeneity was evaluated using the I² statistic, and Forest plots were generated using RevMan 5.4. Narrative synthesis was conducted for studies with outcomes not reported as HRs. Minimal adjustment models (age and sex) were preferred for meta-analysis to avoid over-adjustment, though some studies used maximally adjusted models, which could obscure causal relationships.
Study results
An initial search in March 2023, updated in May 2024, retrieved 33,922 studies from nine databases, with an additional 3,097 studies in the update. After removing duplicates, 16,520 studies underwent title and abstract screening, leading to 292 full-text articles for further review. Ultimately, 13 studies met the inclusion criteria for this analysis, focusing on mortality outcomes in T2D. Of these, seven studies provided sufficient data for meta-analysis, while six were included in a narrative synthesis.
The 13 studies, published between 2010 and 2021, included 573,173 participants with T2D and were conducted in various countries: four in the United States of America (USA), three in the United Kingdom (UK), two each in New Zealand and Australia, and one each in Canada and Singapore.
Most studies compared ethnic groups against White ethnicity, except for one study that used Chinese ethnicity as the reference group. Follow-up durations ranged from 4 to 18 years. Using the NOS, 12 studies were rated as "Good" for methodological quality, while one was rated "Poor" due to inadequate follow-up. However, the diverse study designs and population characteristics may impact generalizability, particularly outside of North America, the UK, and Australasia.
Meta-analysis revealed significant findings regarding all-cause mortality risk. Four studies comparing South Asian ethnicity with White ethnicity reported a lower mortality risk for South Asians, with a hazard ratio (HR) of 0.68 (95% CI 0.65-0.72). Similarly, five studies examining Black ethnicity demonstrated a reduced mortality risk compared to White ethnicity, HR 0.82 (95% CI 0.77-0.87). For Chinese ethnicity, two studies indicated a lower mortality risk compared to White ethnicity, HR 0.57 (95% CI 0.46-0.70), though with high heterogeneity (I² = 90%), suggesting variability in study populations or methodologies.
Narrative synthesis highlighted additional findings. Indigenous populations, including Māori in New Zealand and Indigenous Australians, faced higher mortality risks compared to European or Anglo-Celtic groups. Mediterranean and Arabic ethnicities in Australia exhibited lower mortality risks compared to Anglo-Celtic populations. Studies from the USA and the UK reported varying mortality risks among Hispanic, Asian, African, and Caribbean ethnicities, reflecting nuanced patterns of ethnic disparities.
One study from Singapore uniquely used a non-White reference group, showing higher mortality risks among Malay and Indian ethnicities compared to Chinese ethnicity. These findings highlight the complexity of ethnicity-related mortality differences and the need for further research to uncover underlying factors.
Conclusions
To summarize, this study found that individuals with T2D of South Asian, Black, and Chinese ethnicity have significantly lower all-cause mortality risks compared to White ethnicity, with reductions of 32%, 18%, and 43%, respectively. Conversely, Indigenous populations, such as Māori New Zealanders and Indigenous Australians, face higher mortality risks. The review, encompassing 13 studies and over 500,000 participants, demonstrated consistent findings across diverse settings. However, the authors note limitations, including reliance on broad ethnic categories that may mask subgroup differences and potential over-adjustment in statistical models due to variable confounder selection across studies.