However, subsequent carefully controlled studies by Tinsley et. The earlier reports created a dilemma for the Food and Drug Administration since by terms of the Dulaney Amendment it is illegal to add a known carcinogeic substance to human food or feed for food producing animals. Here was an essential nutrient which was reported to cause cancer yet it was needed to prevent deficiency symptoms in diets low in selenium. Furthermore, selenium levels of food from animals fed natural rations adequate in selenium would be as high or higher than would result from low level supplementation. Since 1979, the FDA has permitted the supplementation of livestock rations with selenium at the level of 0.1 ppm either as part of the complete diet or in a mineral mixture offered free choice.
Selenium has some interesting implications in human nutrition.
Children suffering from kwashiorkor, a severe nutritional deficiency, have been shown by Scharz to respond to selenium supplementation. Other studies have shown that the presence of selenium in the diet is negatively correlated with breast cancer. It has also been suggested, as shown in Table 1, that higher levels of selenium in the blood may be inversely related to cancer mortality. The highest concentration in human blood was in Rapid City, South Dakota while Lima, Ohio is a deficient area. Hypertensive and arteriosclerotic heart disease is reported to be less frequent in areas where relatively greater amounts of selenium is present in drinking water.