Zinc is important for the human immune system, especially for children. Zinc is present in numerous human enzymes and is active in the uptake of vitamin A, another component crucial for human health in developing countries. Zinc deficiency is considered to be behind 20 % of the child mortality in poor countries. This is in parity with the mortality caused by malaria in Africa.
Zinc in soils, in crops and in food intake has been investigated in central Mali in the Niger inland delta. Almost all soils have been found to be zinc deficient, having less than 0.8 mg Zn/kg as DTPA-extractable. Only in the close surrounding of villages higher levels have been detected, probably caused by littering zinc-carbon batteries. The zinc deficiency is probably due ti inherent low content of zinc in the soils and to some extent due to excessive phosphate application by fertilisers.
Crops are low in zinc, this is especially the case for rice. Food intake of zinc has been assessed by analyzing 20 meals for zinc, iron and energy content. By assuming that people eat enough to satisfy their energy need it has been found that the zinc intake in adults as well as in children is about half the recommended. This is possibly an optimistic assumption as food shortage is common. For iron the intake is on the contrary more than the recommended. Nevertheless anemia in women and children is common illustrating the fact the the trace elements like iron and zinc are available for human uptake only to a small extent in the cereal dominated diet. Food preparation like fermentation and germination may increase the availability of the trace metals.
The zinc deficiency in soils has negative effects on the health, especially for children. There is an accumulated incidence of mortality at weaning age when children are exposed to infections via food and water from the environment. The zinc deficiency may also have serious effects on crop yields as well. Wheat is especially sensitive in this respect and yield reduction amounting to as much as 50 % may occur. Wheat cultivation is increasing in Mali but has met difficulties such as low yields and poor returns for the farmers. Fertilisers with trace metals are not available in Mali but would be needed both from crop quantity and crop quality aspects. Supplementation in food items has been tested in several countries but is not applicable in Mali as most of the food is locally produced and consumed.
