Some forms of chromium are known to be toxic, but those are not present naturally in foods or contained in currently available dietary supplements. Copper is necessary for proper development of connective tissue, nerve coverings, and skin pigment. The new RDA is 900 mcg a day for both men and women. No more than 10 mg a day should be consumed, as too much causes liver damage. Based on research into how much iodine the thyroid needs to properly regulate enzyme and metabolic processes, an RDA of 150 mg a day was established for both men and women.
Most food sources have little iodine, but iodized salt is a dietary source.
To avoid over-absorption of iodine by the thyroid, adults should not consume more than 1.1 mg daily. Nuts, legumes, tea and whole grains are rich sources of manganese. The report sets an adequate intake level for manganese at 2.3 mg per day for men and 1.8 mg per day for women. The upper intake limit is set at 11 mg for adults, based on a recent study showing that no adverse health effects occurred when this amount was consumed on a chronic basis. Neurological side effects, similar to symptoms caused by Parkinson's disease, were observed in an earlier study among participants who consumed 15 mg a day.