New evidence on the nutritional and functional benefits of biofortified crops

A review of the evidence: the nutritional and functional effects of vitamin A biofortified crops

Amanda Palmer

Johns Hopkins University, Baltimore, Estados Unidos de América

Introduction / Objectives: Vitamin A deficiency is a persistent problem in the developing world. Several strategies have been introduced to control vitamin A deficiency and its public health consequences, including an increased risk of mortality, especially among young children, and potentially blinding eye disease. These include semi-annual high-dose supplementation of children 6-59 months of age, industrial-scale fortification of food vehicles such as sugar or oil, and the promotion of dietary diversification. Biofortification offers a new, complementary approach that may be particularly important in reaching and ensuring adequate dietary vitamin A intakes among the rural poor. Conventional plant breeding techniques have proven successful in generating cultivars of orange-fleshed sweet potato, maize, and cassava with enhanced provitamin A carotenoid profiles. Our objective was to review the emerging evidence on provitamin A biofortified crops as an efficacious and effective strategy to control vitamin A deficiency, considering the impact on both biochemical and functional measures of vitamin A status. Development Sweet potato was the first of the provitamin A crops to be considered in nutrition trials by the International Potato Center, as many existing varieties had very high provitamin A carotenoid contents (e.g., 30-100 μg/g of beta-carotene or greater). Efficacy studies carried out in Mozambique and South Africa showed significantly increases in both serum retinol and vitamin A liver stores as measured by the modified-relative-doseresponse test, respectively. The introduction of orange-fleshed sweet potatoes is also one of the few agriculture-based nutrition interventions to have been tested in adequately designed effectiveness studies. These show that introduction of orange sweet potatoes in rural Uganda via either an intensive- or reduced-input strategy significantly increased vitamin A intakes. Similar results were reported from effectiveness research carried out in Mozambique. The Uganda research also reported a decreased prevalence of marginal vitamin A status among preschool-aged children and women of reproductive age attributable to the introduction of the biofortified crop. Maize is the most produced staple crop worldwide. Although there is broad natural diversity in the carotenoid profile of this staple, most varieties provide very little provitamin A (<1.5 μg/g). Biofortified cultivars developed under the guidance of the International Maize and Wheat Improvement Center have reached 15 μg/g of beta-carotene. One cultivar with this profile is being tested in a series of nutrition efficacy trials in Zambia, of which three have now been completed and one is underway. Results to date demonstrate a significant impact on serum beta-carotene concentration, total body vitamin A measured by a retinol isotope dilution methodology, and dark adaptation after three to six months of regular consumption by preschool-aged children. They also suggest a decreased prevalence of low milk retinol concentration after a three-week intervention in lactating mothers; however, this latter finding was not statistically significant. Additional data will be presented regarding impact on serum retinol in preschool-aged children, plasma retinol in lactating mothers, and the role that genetic polymorphisms may play in the response to this intervention. Effectiveness studies for biofortified maize have not yet been undertaken, as released cultivars do not yet provide the targeted 15 μg/g of betacarotene. Cassava is a drought-tolerant staple crop, widely consumed in Latin America, Africa, and Asia. Varieties with naturally higher provitamin A carotenoid content have been identified by the International Centre for Tropical Agriculture and used for biofortification breeding programs. One cultivar with a beta-carotene content of ~5 μg/g was tested in Kenya in 2012. This feeding trial enrolled deficient school-aged children to receive meals twice daily for 4.5 months. The authors demonstrated a significant impact on both beta-carotene and retinol concentration in serum. The intervention did not have a measureable impact on dark adaptation; however, analysis was limited to between-group differences at follow-up. It is possible that an impact would have been detectable at the individual level. Now that the breeding target of 15 μg/g has been met, a second efficacy trial is underway in Nigeria to test the impact of regular biofortified cassava consumption on total body vitamin A in young children. Conclusions: Taken together, the available research on “vitamin A” biofortified crops clearly demonstrates that provitamin A carotenoids in sweet potato, maize, and cassava are bioavailable. The regular consumption of these crops in the context of low vitamin A intakes and poor status can improve body stores of vitamin A, raise circulating concentrations, and improve dark adaptation. Although evidence is currently limited to sweet potatoes, the effectiveness research also suggests that the introduction of provitamin A biofortified crops can be successfully taken to scale as an intervention for vitamin A deficiency control. Key words vitamin A, carotenoids, biofortification, efficacy, effectiveness.