Sulfur (S) is a mineral that occurs in our diet as a component of other compounds. It is present in the vitamins thiamin and biotin; and it is present in two of the amino acids (cysteine and methionine) that are found in our body’s proteins, as well as those that we eat. When we need to synthesize sulfur-containing compounds, the ultimate source of that sulfur is almost invariantly one of those amino acids. Because sulfur is a component of all proteins, deficiency is virtually unknown. Toxicity is also rare because the body can excrete excess sulfur in the urine.