Diabetes is not caused by cassava toxicity. A study in a Tanzanian community

To test the hypothesis that consumption of cassava with liberation of cyanide causes diabetes in malnourished individuals.

Glucose tolerance was assessed in two rural communities in Tanzania; in one (Nyambori), the main source of calories was cassava; and in the other (Uswaa), cassava was rarely eaten. Undernutrition was prevalent in both communities. The people of Nyambori were known to have high dietary cyanide exposure for many years from consumption of insufficiently processed cassava. Of the 1435 people in Nyambori greater than or equal to 15 yr old, 1067 (74%) were surveyed, and 1429 of 1472 (97%) eligible subjects in Uswaa were surveyed. All had 75-g oral glucose tolerance tests and measurement of BMI. Plasma and urine thiocyanate and blood cyanide also were measured in some subjects.

Mean +/- SD plasma and urine thiocyanate levels in Nyambori were 296 +/- 190 and 497 +/- 457 microM (n = 204), respectively, compared with 30 +/- 37 and 9 +/- 13 microM, respectively, in Uswaa (n = 92) (P less than 0.001 for all differences). The mean blood cyanide level in Nyambori was elevated (1.4 [range 0.1-30.2] microM; n = 91). The prevalence of diabetes in the cassava village (Nyambori) was 0.5% compared with 0.9% in Uswaa (NS). The prevalence of IGT was similar in the two villages in the 15- to 34- and the 34- to 54-yr-old age-groups; but in those greater than or equal to 55 yr old, IGT was higher in Nyambori (17.4 vs 7.2%, P = 0.029). Mean fasting and 2-h blood glucose levels were slightly higher in Nyambori village after adjusting for age, sex, and BMI (4.5 vs. 4.2 and 5.0 vs. 4.4 mM, respectively).

High dietary cyanide exposure was not found to have had a significant effect on the prevalence of diabetes in an undernourished population in Tanzania. Cassava consumption is thus highly unlikely to be a major etiological factor in so-called MRDM, at least in East Africa.