Plant sources of vitamin A and human nutriture: how much is still too little?

In a randomized controlled 12-week feeding trial among malnourished, anemic, and largely vitamin A-deficient Ghanaian preschool children, the hypothesis that the ability of provitamin A carotenoids in dark green, leafy vegetables (DGLV) to raise vitamin A status in different formats--with or without fat and with fat plus anthelmintic treatment for intestinal worms--was tested by comparison with a low vitamin A fare and with pure chemical beta-carotene. The 12-week increments in retinol concentrations over baseline ranged from 5% to 44%, but over half of the DGLV-fed population had persistently low circulating retinol. The very modest impact on vitamin A status of these maneuvers to optimize dietary use of provitamin A in DGLV has major implications for public policy to eradicate hypovitaminosis A.