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OBJECTIVE: Studies on phenotypes of diabetes in Africa are inconsistent. We assessed the role of ?-cell dysfunction and insulin resistance on pre-diabetes and diabetes. METHODS: We included 1890 participants with mean age of 40.6 (SD11.9) years in a cross-sectional study among male and female adults in Tanzania during 2016 to 2017. Data on C-reactive protein (CRP), alpha-acid glycoprotein (AGP), HIV, oral glucose tolerance test (OGTT), body composition and insulin were collected. Insulinogenic index and HOMA-IR were used to derive an overall marker of ?-cell dysfunction and insulin resistance which was categorised as follows: normal ?-cell function and insulin sensitivity, isolated ?-cell dysfunction, isolated insulin resistance, and combined ?-cell dysfunction and insulin resistance. Pre-diabetes and diabetes were defined as 2-hour OGTT glucose between 7.8-11.0 and ? 11.1 mmol/L, respectively. Multinomial regression assessed the association of ?-cell dysfunction and insulin resistance with outcome measures. RESULTS: ?-cell dysfunction, insulin resistance, and combined ?-cell dysfunction and insulin resistance were associated with higher pre-diabetes risk. Similarly, isolated ?-cell dysfunction (adjusted relative risk ratio (aRRR) 4.8 (95% confidence interval (CI) 2.5, 9.0), isolated insulin resistance (aRRR 3.2 (95% CI 1.5, 6.9), and combined ?-cell dysfunction and insulin resistance (aRRR 35.9 (95% CI 17.2, 75.2) were associated with higher diabetes risk. CRP, AGP and HIV were associated with higher diabetes risk, but fat mass was not. 31%, 10% and 33% of diabetes cases were attributed to ?-cell dysfunction, insulin resistance, and combined ?-cell dysfunction and insulin resistance, respectively. CONCLUSIONS: ?-cell dysfunction seemed to explain most of diabetes cases compared to insulin resistance in this population. Cohort studies on evolution of diabetes in Africa are needed to confirm these results.