Aims Black Africans are disproportionally affected by type 2 diabetes, but the pathophysiology is poorly understood. The study aimed to examine the effect of sex and age on insulin sensitivity and insulin response in black South African adults. Methods This cross-sectional study included a random sample of 179 men and 260 women aged 25–74 years with normal glucose tolerance from 5 peri-urban townships in Cape Town, SA. Insulin sensitivity (insulin sensitivity index, ISI0,120) and response (insulinogenic index, IGI), and the disposition index (DI, ISI0,120 × IGI), derived from an oral glucose tolerance test, were measured. Results Although men were older (median [interquartile range]: 39 [30–48] vs. 35 [29–44], P = 0.021) and had significantly lower BMI than women (22.6 [20.0–25.3] vs. 31.0 [25.9–35.7] kg/m2, P = 0.001), DI was not different (P = 0.740), but ISI0,120 was higher (P = 0.007) and IGI was lower (P = 0.074) in men than women, adjusting for age and BMI. With increasing age, DI (β (95%CI): −24.4 (−36.3 to −12.5), P < 0.001) and IGI (β (95%CI): −4.9 (−7.5 to −2.2), P < 0.001) decreased similarly in both sexes, but ISI0,120 did not change (β (95%CI): 0.005 (−0.20 to 0.03), P = 0.675). Conclusion Black South African women with normal glucose tolerance have lower insulin sensitivity than their male counterparts, but increase their insulin response to maintain normoglycemia. With increasing age, insulin sensitivity remains unchanged, but the insulin response decreases at a similar rate in men and women.
