Provitamin A carotenoid-biofortified maize consumption increases pupillary responsiveness among Zambian children in a randomized controlled trial

Background: Impaired dark adaptation is an early functional indicator of vitamin A deficiency that may be sprevented by regular dietary intake of foods containing provitamin A carotenoids. Objective: We tested the impact of provitamin A carotenoid-biofortified maize consumption (~15 μg ß-carotene/g) on dark adaptation in Zambian children. Methods: We used a cluster-randomized trial of children aged 4-8 y (n = 1024) in Mkushi District, Zambia, and compared the regular consumption (2 meals/d, 6 d/wk for 6 mo) of biofortified orange maize (OM) to white maize (WM). The primary outcome was the serum retinol response. In a random sample (n = 542), we used a digital pupillometer to test pre- and postintervention responses to graded light stimuli (-2.9 to 0.1 log cd/m2) in a dark-adapted state. Results: At baseline, 11.7% of the children had serum retinol < 0.7 μmol/L, 14.4% had impaired dark adaptation (pupillary threshold ≥ -1.11 log cd/m2), and 2.3% had night blindness. The mean ± SD pupillary responsiveness to light stimuli was poorer at baseline in the OM group (16.1% ± 6.6%) than the WM group (18.1% ± 6.4%) (P = 0.02) but did not differ at follow-up (OM: 17.6% ± 6.5%; WM: 18.3% ± 6.5%). Among children with serum retinol < 1.05 μmol/L at baseline, there was greater improvement in pupillary responsiveness in the OM group (2.2%; 95% CI: 0.1%, 4.3%) than the WM group (0.2%; 95% CI: -1.1%, 1.5%; P = 0.01), but there were no differences in children with adequate baseline status. We found no effect of treatment on pupillary threshold or night blindness. Conclusions: The regular consumption of provitamin A carotenoid-biofortified maize increased pupillary responsiveness among children with marginal or deficient vitamin A status, providing evidence of a functional benefit to consuming this biofortified crop.