Marginal iron intake is so widespread that some nutritionists want to have iron added to common foods like bread and cereals, just as some vitamins now are. However, excess iron in the body also leads to problems, and this has made the proposal controversial. In regions with iodine-deficient soils, food may not contain enough iodine to meet body needs. This makes sense because fluoride ions are incorporated along with calcium and phosphate ions in the crystalline structure of which both bones and teeth are constructed. But it may have other functions.
Humans get most of their fluoride in drinking water.
In regions where the natural amount is less than 1 ppm, many communities add enough fluoride to bring the concentration up to 1 ppm. Perhaps because the range between optimum and excess is more narrow for fluoride than for most minerals in the diet, water fluoridation has been controversial. Leaving aside the philosophical and political questions raised by proponents and opponents of fluoridation, the safety and efficacy of this public health measure has been thoroughly established. Zinc supplements are popular for their supposed antioxidant properties and to hasten the recovery from colds. Excessive intake of zinc causes a brief illness.