Glucose-Independent Ethnic Differences in HbA(1c) in People Without Known Diabetes

OBJECTIVE: To determine whether glucose-independent differences in HbA(1c) exist between people of African, South Asian, and Chinese ethnicities. RESEARCH DESIGN AND METHODS: Data from 6,701 people aged 19–78 years, without known diabetes, from Mauritius, and participating in the population-based Non-Communicable Disease Surveys of the main island and the island of Rodrigues were included. Participants were African (n = 1,219 from main island, n = 1,505 from Rodrigues), South Asian (n = 3,820), and Chinese (n = 157). Survey data included HbA(1c), plasma glucose during oral glucose tolerance testing (OGTT), anthropometry, demographics, and medical and lifestyle history. RESULTS: Mean HbA(1c), after adjustment for fasting and 2-h plasma glucose and other factors known to influence HbA(1c), was higher in Africans from Rodrigues (6.1%) than in South Asians (5.7%, P < 0.001), Chinese (5.7%, P < 0.001), or Africans from the main island of Mauritius (5.7%, P < 0.001). The age-standardized prevalence of diabetes among Africans from Rodrigues differed substantially depending on the diagnostic criteria used [OGTT 7.9% (95% CI 5.8–10.0); HbA(1c) 17.3% (15.3–19.2)]. Changing diagnostic criteria resulted in no significant change in the prevalence of diabetes within the other ethnic groups. CONCLUSIONS: People of African ethnicity from Rodrigues have higher HbA(1c) than those of South Asian or African ethnicity from the main island of Mauritius for reasons not explained by plasma glucose during an OGTT or traditional factors known to affect glycemia. Further research should be directed at determining the mechanism behind this disparity and its relevance to clinical outcomes.