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Milk from organic farms has a lower concentration of elements like zinc, iodine and selenium than milk produced by conventional farming methods. The discrepancy is due to the absence of mineral substances in the diets of the cows reared. Animals on organic farms should have their diets supplemented with natural sources of iodine such as seaweed, because it is a very important element for children and pregnant women. The concentration of nutrients in animal food products is linked to the diets of the animals reared. Conventional production methods provide mineral diet supplements, while in organic farming animals depend on the mineral content in soil, which may not be sufficient. Marta Lopez, at the University of Santiago de Compostela compared the mineral and toxic elements of organic and conventional milk taken from over thirty farms located in the northeast of the Iberian Peninsula. The results demonstrated that mineral element content in organic milk is low compared with conventional milk, although no differences were found in the quantity of toxic compounds such as cadmium, which were also detected in very low concentrations. Levels of the elements that are typically supplemented in the diets of livestock in conventional systems - particularly iodine, copper, selenium and zinc are higher than those found in organic milk. The fact that organic milk contains lower levels of elements such as copper and zinc is not a problem because milk is not the primary source of these elements in our diets.