Yellow cassava: efficacy of provitamin A rich cassava on improvement of vitamin A status in Kenyan schoolchildren

Background: Biofortified yellow cassava has great potential to alleviate vitamin A deficiency in sub-Saharan Africa and can be used as a complementary approach to other interventions. However, direct evidence whether yellow cassava can significantly contribute to the vitamin A intake and status of populations is required. The overall aim of this thesis is to provide proof of principle whether biofortified yellow cassava can improve the vitamin A status of schoolchildren in Kenya. Methods: The research was conducted in Kibwezi district, Eastern Kenya. First the effect of daily consumption of yellow cassava was assessed in 342 primary school children in Kenya in a randomized controlled feeding trial with serum retinol concentration as primary outcome. Furthermore we investigated the sensory and cultural acceptability of yellow cassava in a cross-sectional study (n=140) in three primary schools for children as well as their caretakers. Next we studied the diagnostic performance of several proxy markers to assess vitamin A deficiency in comparison with serum retinol concentration as a field based method to assess vitamin A deficiency (n=375). And last we used the dietary intake data of children in the randomized controlled trial to model the potential contribution of yellow cassava to the nutrient adequacy of micronutrient intake using linear programming. Results: The randomized controlled feeding trial collected complete data for 337 children with a compliance of 100%. Primary analyses (per protocol) showed that serum retinol concentrations in the yellow cassava group, increased with 0.04 μmol/L (95%CI: 0.00‒0.07 μmol/L) compared to the white cassava group and secondary analyses showed that serum β-carotene concentration increased with 524% (448%‒608%). No evidence of effect modification by initial vitamin A status, zinc status, or polymorphisms in the β-carotene monooxygenase gene was found. In the acceptability study 72% of caretakers and children were able to detect a significant difference in taste between white and yellow cassava and indicated to prefer yellow cassava because of its soft texture, sweet taste and attractive color. Serum concentrations of retinol binding protein, transthyretin and C-reactive protein combined showed excellent diagnostic performance in estimating vitamin A deficiency in primary school children, with an area under the curve of 0.98. Adding yellow cassava to the diet as a school lunch improved the nutrient adequacy of the diet of schoolchildren, however, even with the addition of nutrient dense foods such as fish and oil, nutrient adequacy could not be ensured for fat, riboflavin, niacin, folate and vitamin A. Conclusions: Consumption of yellow cassava is acceptable and improves the serum retinol concentrations of primary school children in Kenya. The combination of three proxy markers is a promising approach to measure vitamin A deficiency in a low resource setting. Yellow cassava contributes to a better nutrient adequacy but should be accompanied by additional dietary guidelines and interventions to fill the remaining nutrient gaps.