Adding iodine in the cultivation of lettuce on water can improve the nutritional value of lettuce for humans. Worldwide iodine deficiency is a large health problem. Wageningen UR Greenhouse Horticulture developed, together with fertiliser manufacturer SQM Europe BV, a cultivation method to enrich lettuce with iodine.
Biofortification of green vegetables with iodine offers perspectives for increasing iodine uptake by humans. Worldwide some two billion people are contending with iodine deficiency. According to the World Health Organisation (WHO) this is one of the main current health problems. A deficiency of this food element presents a particular risk to pregnant women and young children by causing developmental disorders. Thyroid problems and mental disorders may occur in older children and adults.
Iodine deficiency in particular occurs in areas where soils have low iodine contents. Crops grown on such soils contain too little of this element. This nutrient deficiency can largely be solved by adding iodine to salt for, e.g., bread. Bread consumption, however, decreases and there are various cultures in which little bread is eaten. An alternative source of iodine is therefore required. Vegetables seem to be a good alternative.
Recommended daily intake
Scientist Wim Voogt explains: “It was found in earlier research that crops show a good iodine uptake if available as free element. Iodine is mainly found in leaves and not in fruits or seeds. Because iodine is easily absorbed by soil, we have set up an experiment with lettuce cultivation in water. This cultivation method is becoming more popular in an increasing number of areas. We focussed on the addition of iodine in two different forms, i.e., iodide (I-) en iodate (IO3-). We used several concentrations and recorded the amounts that were taken up.”
These experiments show that addition of iodide to the nutrient solution results in a significant increase in the iodine content of lettuce. It was also found that there was no effect on crop development or on evapotranspiration. The iodine is mainly present in the outer leaves of the lettuce head. Iodide is taken up easier than iodate. No differences were found between the effect of iodine in the nutrient solution between a winter and a summer crop.
A consumption of fifty gram lettuce per day grown on the nutrient solution with the highest iodine concentration resulted in an amount of iodine in the leaves that is sufficient to provide 22 per cent (in case of iodate addition) and 25 per cent (in case of iodine addition) of the recommended daily intake.