Low cyanide exposure from consumption of cassava in Dar es Salaam, Tanzania

Ecological variation of intake of cassava food and dietary cyanide load in Nigerian communities

AIM

To study the ecological variation of intake of cassava foods and dietary cyanide load.

DESIGN

Ecological study design.

SETTING

Five communities in south-western Nigeria where tropical ataxic neuropathy (TAN) was described as endemic (area A), 11 communities in south-western Nigeria where TAN was described as absent (area B), and five communities in northern Nigeria (area C).

SUBJECTS

Subjects were randomly sampled from selected communities. Intake of cassava foods was estimated from dietary history and dietary cyanide load was estimated from urine thiocyanate concentrations. Residual cyanogens in cassava food samples from the community markets were determined.

RESULTS

In total, 1272 subjects from 21 communities - 238 from area A, 659 from area B and 375 from area C - were selected. Intake of cassava food per person per week was 17 meals in area A, 10 meals in area B, and one meal in area C. Geometrical mean urine thiocyanate concentrations were 73 micromol l(-1), 51 micromol l(-1) and 17 micromol l(-1) in areas A, B and C, respectively. Mean residual cyanogen content in cassava food samples was 16 mg HCN eq kg(-1) (confidence interval (CI) 13-18) in area A, and 13 mg HCN eq kg(-1) in area B (CI 11-14).

CONCLUSION

This study shows that the intake of cassava foods and dietary cyanide load is high in several communities in south-western Nigeria, predominantly in communities where TAN has been reported. Dietary cyanide load in these communities appears to be determined by the combination of frequency of intake and cyanogen content of cassava foods. Measures to improve the effectiveness of removal of cyanogen from cassava roots during processing are needed in the affected communities.

High cassava production and low dietary cyanide exposure in mid-west Nigeria

OBJECTIVE

To investigate if high cassava production levels indicate high consumption and high dietary cyanide exposure in three villages situated within the area of Nigeria with higher cassava production than predicted by a geographic model for cassava production in Africa.

DESIGN

Exploratory assessment of: cassava production and processing by qualitative research methods and quantification of residual cyanogens in products; cassava consumption by food frequency and weighed food records and dietary cyanide exposure by urinary thiocyanate and linamarin.

SETTING

Rural communities of Afuze, Ebue and Ofabo in mid-west Nigeria.

SUBJECTS

110 subjects from 42 households in three villages for food frequency interviews; 118 subjects in nine Ofabo households for weighed food records.

RESULTS

Cassava cultivation was reported to have increased in the preceding 20 years. It was consumed daily by 37 (88%) households, but its mean contribution to daily energy intake was only 13% The range of residual cyanogens in cassava foods was 0 to 62 mg HCN equivalent/kg dry weight (dw). Ten samples (19%) had levels above the 10 mg HCN equivalent/kg dw FAO/WHO safety limit. Mean urinary thiocyanate and linamarin were 51 and 20 micromol/L, indicating low cyanogen intake and dietary cyanide exposure.

CONCLUSION

High cassava production levels did not result in high consumption and high dietary cyanide exposure levels, therefore cassava production levels cannot be used to predict consumption or cyanide exposure levels in the study area. A large part of the production is explained by intensive sales.