The study comprises an open-label randomized controlled trial investigating the efficacy of consuming a daily ration of pro-vitamin A biofortified cassava on vitamin A status of Nigerian children, aged 3-4 years old (n=200).

Objective: The primary objective is to assess the efficacy of daily consumption of pro-vitamin A rich cassava during 10 weeks on body retinol pools of 3-4 year old children in Nigeria after high-dose vitamin A supplementation. The secondary objectives are: 1) To investigate the effect of daily consumption of pro-vitamin A rich cassava on functional indicators such as nutritional anaemia and gut integrity; 2) To investigate the effect of zinc deficiency and genetic polymorphisms in the Beta-Carotene Oxygenase 1 (BCO1) and related genes on the efficacy of pro-vitamin A rich cassava consumption; 3) To compare the skin colour in the palm of the hand of each participant with their serum retinol levels using a handheld non-invasive spectrophotometer.

Study design: Open-label (single-blinded) randomized controlled trial with two parallel groups Study population: Pre-school children, aged 3-4 years living in Osun State area, South-Western Nigeria. Children (n=750) will be screened for eligibility. Out of these, n=250 will undergo a 4-week run-in phase. n=200 children will be randomly allocated to two different treatments: 1) Yellow cassava providing ~50% of the recommended daily allowance (RDA) for vitamin A; 2) White cassava.

Main study parameters/endpoints: The primary outcome was the difference in body retinol pools between groups 1 and 2 at the end of intervention; however, due to the inability to assess body retinol pools, the modified primary outcome is the difference in serum retinol concentrations between groups 1 and 2. Other outcome measures include: other vitamin A status indicators (β-carotene, retinol binding protein, transthyretin), inflammatory markers, iron status indicators, anthropometrics, gut integrity, and thyroid function.

Inclusion Criteria:

• Aged 36 - 59 months (verified by birth certificates, vaccination cards or other formal documentation)
• Apparently healthy
• Parental informed consent

Exclusion Criteria:

• Frequently absent (>20% of feeding days) during run-in
• Children not assenting during blood collections
• Signs or history of infectious or systemic diseases (e.g. tuberculosis, sickle cell anaemia)
• Mental status that is incompatible with the proper conduct of the study
• Current participation in other research
• Food allergy related to the intervention foods