medwireNews: At least a third of people diagnosed with type 2 diabetes in sub-Saharan Africa are neither overweight nor particularly insulin resistant, say researchers.
Davis Kibirige (Medical Research Council/Uganda Virus Research Institute and London School of Hygiene and Tropical Medicine Uganda Research Unit, Entebbe) and colleagues say their findings have “major implications for screening or diagnosis because age and BMI are widely used to clinically differentiate between type 1 and type 2 diabetes.”
Among 500 people who were newly diagnosed with diabetes and did not have autoantibodies, 32% had a BMI below 25.0 kg/m2, at an average of 22.2 kg/m2. They were the same age, on average, as those with higher BMIs, but had significantly less total body fat, at a median of 22.5% versus 42.0%, as well as less visceral fat.
“These individuals showed biochemical features that are consistent with pancreatic beta cell dysfunction rather than insulin resistance,” write the researchers in Diabetologia.
The median fasting blood glucose levels were similar in lean and non-lean people, at 9.1 and 8.4 mmol/L (164 and 151 mg/dL), respectively, and the same was true for 30-minute and 2-hour blood glucose. Yet levels of insulin and of C-peptide were significantly lower, with median fasting levels of 29.17 versus 48.61 pmol/L and 0.33 and 0.53 nmol/L, respectively.
Insulin resistance was also significantly less in the lean people, with an average HOMA2-IR value of 0.89 compared with 1.32 in non-lean people, whereas pancreatic beta-cell function was significantly poorer, as reflected by median insulinogenic index values of 0.8 versus 1.6 pmol/mmol.
“These findings are in direct contrast with the conventional picture of diabetes in adulthood, consisting of overweight or obesity and insulin resistance, with pancreatic beta cell failure occurring later during the condition,” say Kibirige and team.
They note that their findings are consistent with population-based studies from sub-Saharan Africa, showing that around two-thirds of people with type 2 diabetes are not overweight or obese.
The team also says their research fits with recent evidence that beta-cell dysfunction is a major cause of type 2 diabetes in South Asian people, rather than insulin resistance as previously believed due to the propensity to central obesity in this population.
“In this respect, the lean type 2 diabetes phenotype in South Asia may share a common aetiological mechanism with our Ugandan adult population,” say the study authors.
They stress that current management guidelines for type 2 diabetes are based on research primarily in overweight or obese people of European ancestry living in high-income countries.
“It is unclear whether these therapeutic interventions have the same effectiveness in sub-Saharan Africa where many adult patients are relatively young, lean in body size and not insulin-resistant,” they say.
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