Despite being one of the most poorly absorbed of the trace minerals (generally less than 5% is absorbed), manganese deficiencies are far less common than are toxicities. It functions as a co-factor for enzymes involved in antioxidant functions, and is involved in the meta-bolism of carbohydrates, cholesterol, and amino acids. The role of manganese in amino acid metabolism makes it important for the synthesis of proteins needed for bone growth and maintenance, as well as for wound healing.

Molybdenum is a co-factor for only four enzymes, and the function of one of these enzymes is not well-understood. The average intake of the United States population is usually well-above the RDA; deficiencies are unknown in healthy individuals and the risk of toxicity in humans is very low.

Chromium is a popular dietary supplement, yet despite the hype, its proposed benefits have not been supported by the results of intervention trials. There is essentially no credible evidence that it promotes weight loss, or that it improves muscle mass with resistance training. Perhaps even more surprising, recent studies have failed to conclusively demonstrate that chromium can enhance the ability of insulin to control blood glucose, and no progress has been made in identifying the means by which chromium might exert its biological affects. Also, chromium deficiency in humans has been observed only in hospitalized patients who had been receiving 100% of all nutrients intravenously for an extended period. For these reasons, some experts now question chromium’s designation as an essential nutrient.