Selenocysteine

What is selenocysteine?

Selenocysteine is a nonessential amino acid ^[1]. It can be produced in your body from another amino acid cysteine by replacing the sulfur by selenium ^[1]. In foods, selenocysteine is incorporated into proteins.

Selenocysteine abbreviation (symbol): Sec

Selenocysteine Functions in the Human Body

Selenocysteine is:

• A building block of selenium-containing proteins called selenoproteins, which act mainly as enzymes, for example, in the conversion of the thyroid hormone T₄ (thyroxine) into its active form T₃ (triiodothyronine) ^[2,3]
• A glucogenic amino acid — it can be converted into glucose ^[6]

Foods High in Selenocysteine

• ANIMAL FOODS: meat, fish, cheese ^[3,4]
• PLANT FOODS: cereals (corn, wheat, oats, rice), Brazil nut, walnuts ^[3,4]

Foods low in selenocysteine: fruits, vegetables, legumes

Selenocysteine Supplements

Available nonprescription (over-the-counter) oral forms of selenocysteine supplements:

• L-selenocysteine
• Se-methyl selenocysteine

Selenocysteine Health Benefits

Selenocysteine supplements are one of the sources of selenium, which is an essential mineral and antioxidant.

Heavy metals, such as mercury (Hg), bind to selenocysteine in the gut and inhibit the absorption of both selenocysteine and mercury, but there is INSUFFICIENT EVIDENCE about the effectiveness of selenocysteine supplements in removing heavy metals from the body, boosting immunity or treating cancer ^[5,7].

Selenocysteine Safety: Side Effects, Toxicity

Side effects. Selenocysteine supplements in high doses may cause nausea, vomiting, diarrhea, garlic breath odor, fatigue, itchiness, tingling and hair and nail brittleness ^[5].