There is more sulfur in the human body than magnesium, sodium, or chloride. The chemical symbol for sulfur is the letter S. Sulfur is a major mineral that often occurs with other nutrients. Sulfur is part of the important antioxidant glutathione. Sulfur is also an important part of coenzyme A, which is central to energy metabolism. Sulfur is part of the methyl donor S-adenosylmethionine (SAMe). Sulfur is part of biotin and vitamin B1 (thiamin).
Summary for Sulfur
Main functions: needed for the antioxidant glutathione, part of coenzyme A, and part of the methyl donor SAMe.
Adequate Intake: none established.
Toxicity is not known.
Tolerable upper intake level has not been set.
Deficiency: not known.
Sources: food with sulfur-containing amino acids (methionine and cysteine), onions, garlic, cabbage, and Brussels sprouts.
Forms in the body: found in glutathione, coenzyme A, methionine, cysteine, and SAMe.
The two sulfur-containing amino acids are methionine and cysteine. Protein can be stabilized with the amino acid cysteine. Cysteine has a side chain that contains sulfur. These side chains can link together to form disulfide bridges (disulfide means
Figure 10-7 The human insulin protein uses disulfide bridges for stability.
two sulfurs). These disulfide bridges stabilize protein structures, as shown with insulin in Figure 10-7. The disulfide bridges also help to fold and shape proteins. The more rigid tissues such as those found in skin, hair, and nails have a high content of the protein keratin. Keratin is a type of protein that is tough and insoluble.
Disulfide bridges give extra strength to nails and hair by cross-linking the keratin. The more cross-linking, the stronger the tissue becomes. Human hair is approximately 14 percent cysteine. The pungent smell of burning hair is due to the sulfur compounds in hair.
Deficiencies of sulfur are not known except in cases of severe protein deficiency. There are no recommended intakes for sulfur and there are no upper levels set. Sulfur is easily and efficiently absorbed as part of cysteine and methionine or as inorganic sulfate. To summarize, sulfur is vital for antioxidant activity and energy production. Sulfur is also used to fold and stabilize some proteins. Sulfur is not as well known as many other essential nutrients.
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