"If humans respond similarly, this has important implications for vitamin A-depleted populations consuming maize as a staple food crop," lead authors Julie Howe and Sherry Tanumihardjo from the University of Wisconsin (UoW) told NutraIngredients.com.
"It could potentially eliminate costly and often ineffective supplementation programs, improve morbidity and mortality of mothers and infants during pregnancy and lactation, and reduce the occurrence of night-blindness in adults and blindness in children," they said.
Vitamin A deficiency (VAD) is a public health problem in more than 50 per cent of all countries, especially in Africa and South-East Asia, according to the World Health Organisation, and causes blindness in up to 500,000 children each year. The human body converts beta-carotene in the diet into vitamin A.
Research into biofortication of plants continues to explore ways of increasing the vitamin A status and is being strongly supported by several humanitarian agencies like Harvest Plus, which is actively funding biofortified crop breeding in developing countries, and who funded the new UoW research.
Syngenta has been highly active in producing transgenic beta-carotene-rich rice, and announced in 2005 a new GM rice, called Syngenta Golden Rice II, that produces up to 23-times more provitamin A nutrients than the original beta-carotene-rich Golden Rice This gives the rice a maximum carotenoid level of 37 micrograms per gram of rice and a preferential accumulation of beta-carotene.
However, Greenpeace have been very vocal in criticising the lack of information given on the bioavailability of beta-carotene from the rice in the body, noting that the original variety was also designed to increase intake of this nutrient but children could not get their daily requirement from eating normal quantities of rice.
But concerns about genetic modification is not valid here, the researchers told NutraIngredients.com, because this rice is not GM: "Since this maize has been bred using traditional breeding strategies, GM-skeptic countries shouldn't have issues," they said.
Similar questions regarding the bioavailability of carotenoids from biofortified maize remain, said Howe and Tanumihardjo, despite efforts to produce biofortified maize with provitamin A carotenoids being successful. They set about testing whether feeding beta-carotene-rich maize to vitamin A deficient Mongolian gerbils would improve the vitamin A status of the rodents.
Forty gerbils were fed a standard diet of white maize (low beta-carotene content) for four weeks before starting the experiments. The gerbils were divided into four equal groups and fed an oil control, 60 per cent high-beta-carotene maize, and beta-carotene or vitamin A supplements (matched to high-beta-carotene maize) for four weeks.
The authors, writing in the October issue of the Journal of Nutrition (Vol. 136, pp. 2562-2567), report that concentrations of vitamin A in the liver of the gerbils eating the high-beta-carotene maize group was 150 per cent that of the control group (0.25 versus 0.10 micromoles/gram, respectively), and equalled that of the group receiving the beta-carotene supplements. The vitamin A supplemented group had higher liver concentrations of the vitamin than the other groups (0.56 micromoles/g).
It was found that bioconversion of the beta-carotene to retinol (vitamin A) was about three micrograms of beta-carotene to one microgram of retinol (1.5 mol beta-carotene to 1 mol retinol).
The concentrations of beta-carotene in the livers of the gerbils eating the high-beta-carotene maize was almost double that of the beta-carotene supplement group (26.4 versus 14.1 nanomoles, respectively).
"Biofortified maize adequately maintained vitamin A status in Mongolian gerbils and was as efficacious as beta-carotene supplementation," concluded the researchers.
If such studies can be further reproduced in additional animal studies, and subsequently in randomized control trials with humans, the crops may offer a vital route for reducing the burden of vitamin A deficiency.
The researchers told this website that several research questions still needed answers before commercialization can take place. "The major question is whether humans will respond similarly," they said.
"Other important questions that we are beginning to address include the stability of carotenoids in maize during storage, the effect of food preparation on bioavailability, and sensory evaluations," said Howe and Tanumihardjo.
"Another effort we are pursuing is to determine the contribution of other provitamin A carotenoids to vitamin A status because provitamin A compounds other than beta-carotene are present in significant quantities in maize. These research efforts will help direct breeding efforts to produce the most bioavailable pro-vitamin A biofortified maize varieties."
Enhancement of the nutritional content of plants is gaining ever increasing scientific attention, with a number of genetically modified plants and crops coming to light considered to offer human health benefits, including zeaxanthin to potato tubers, and the omega-3 fatty acid, eicosapentaeoic acid (EPA), to soybeans and brassica, and stearidonic acid (SDA) in canola crops.
However, no GM crops with potentially enhanced health benefits have been approved for human consumption, and consumer acceptance, particularly in Europe, and most notably in the UK, continues to be one of the biggest challenges for these crops.