Trace elements are mineral elements that are needed in small amounts in human nutrition. They are derived from soil and the amount of a particular trace element in a food will depend on the soil the food was grown in. Unfortunately modern farming methods tend to deplete the soil of trace elements, resulting in low amounts in the foods grown on those soils.
Iodine is a trace element needed for proper functioning of the thyroid gland, which regulates the metabolism. Iodine is abundant in the ocean, but in many parts of the world the agricultural soils are low in iodine. It is recommended that people on herbivorous diets pay attnetion to their iodine intake. Seaweeds (such as nori) are good sources of iodine, and iodised salt is another source. Although kelp (kombu) is rich in iodine it is not recommended as it can provide too much iodine, which can be harmful to the thyroid gland. If salt is used, use iodised salt, and eating seaweed a few times a week will also boost iodine intake. Another alternative is supplementation: multivitamiin tablets containing about 100-150 microgrmas of iodine will help ensure an adequate iodine intake.
Selenium is another trace element that is deficient in soils in some parts of the world, resulting in low selenium intakes. As well as being an essential nutrient, selenium has antioxidant activities which can provide health benefits. Eating just one brazil nut per day will significantly boost selenium intake and prevent deficiency.