Form Comparison

Selenomethionine vs Sodium Selenite

How selenomethionine and sodium selenite differ in potency, absorption, tolerance, and cost.

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Quick verdict. Selenomethionine is better absorbed (over 90% vs about 50%) and builds a storage pool by replacing methionine in body proteins, while selenite feeds selenoprotein synthesis directly without that pool. Higher blood selenium from selenomethionine does not prove more selenoprotein activity. Choose selenomethionine to correct low selenium status, and selenite if you want selenium without long-term accumulation.

Side by Side

Selenomethionine Sodium Selenite
Elemental content Varies by product 45.7% elemental selenium
Absorption High Moderate
How it is absorbed Absorbed like methionine, more than 90%. Nonspecifically incorporated into body proteins in place of methionine, which creates a storage pool and higher blood selenium. Inorganic form; about 50% absorbed. Not stored in proteins, but directly available for selenoprotein synthesis.
Typical dose 55-200 mcg daily 55-200 mcg daily
Common uses general supplementation, thyroid autoimmunity (mixed evidence) multivitamins, parenteral nutrition
Side effects Selenosis above the 400 mcg UL: garlic breath, hair and nail loss, GI upset. As for other forms at excess doses.
Cost Low Low
Also called L-selenomethionine selenite
Labels in index 237 43

When to Choose Selenomethionine

Choose selenomethionine when you want the best-retained form. The form used in the SELECT trial, which found no cancer prevention benefit at 200 mcg/day.

Selenomethionine

Well absorbed and the form used in SELECT. It builds up in body protein, which helps repletion and makes chronic overuse more consequential.

What to look for: 50-100 mcg per serving, counting any multivitamin, and only when diet or region suggests low status.

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When to Choose Sodium Selenite

Choose sodium selenite when you want selenium for selenoprotein synthesis without building a protein-bound pool. Lower blood selenium per mcg than selenomethionine does not necessarily mean lower selenoprotein activity.

Sodium Selenite

Less absorbed, but it feeds selenoprotein synthesis directly without building a reserve. The form used in the Graves' orbitopathy trial.

What to look for: Usually a prescribed, time-limited course at a defined dose.

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Products on Titrate

In Titrate's index of NIH label data, 237 labels named as selenium products list selenomethionine and 43 list sodium selenite.

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Selenium does not have its own search category yet. Each product above links to its full label in the NIH database.

Related

References

NIH Office of Dietary Supplements. Selenium: Fact Sheet for Health Professionals.

Clark LC, et al. Effects of selenium supplementation for cancer prevention in patients with carcinoma of the skin. A randomized controlled trial. JAMA. 1996;276(24):1957-1963.

Stranges S, et al. Effects of long-term selenium supplementation on the incidence of type 2 diabetes: a randomized trial. Ann Intern Med. 2007;147(4):217-223.

Thomson CD, et al. Brazil nuts: an effective way to improve selenium status. Am J Clin Nutr. 2008;87(2):379-384.

Lippman SM, et al. Effect of selenium and vitamin E on risk of prostate cancer and other cancers: the Selenium and Vitamin E Cancer Prevention Trial (SELECT). JAMA. 2009;301(1):39-51.

Hurst R, et al. Establishing optimal selenium status: results of a randomized, double-blind, placebo-controlled trial. Am J Clin Nutr. 2010;91(4):923-931.

MacFarquhar JK, et al. Acute selenium toxicity associated with a dietary supplement. Arch Intern Med. 2010;170(3):256-261.

Marcocci C, et al. Selenium and the course of mild Graves' orbitopathy. N Engl J Med. 2011;364(20):1920-1931.