Selenomethionine is an amino acid containing selenium in which selenium replaces the sulfur of the methionine molecule. It is a natural component of the diet and is estimated to represent at least half of all the selenium absorbed through food.
Like other forms of selenium salts and organic selenium compounds, selenomethionine is readily absorbed from the gastrointestinal tract. In a series of studies conducted on humans and animals, in particular those with selenium-poor diets, the bioavailability of selenium deriving from selenomethionine proved to be about 1.5 to 2 times higher than that of inorganic selenium .
Once absorbed, selenomethionine is metabolized in other forms of selenium such as hydrogen selenide, which is also the main metabolite that derives from the inorganic forms of selenium, selenite or selenate, and/or diverted into methionine metabolism pathways and it is conserved in the form of selenoproteins (1).

Selenomethionine or L-selenomethionine is a chemical component recently authorized by the European Commission as a feed additive for all animal species (2).

This chemical compound improves growth performance and reduces stress in animals (3).

With regard to human nutrition, in 2000 the SCF (Scientific Committee on Food, dissolved and incorporated into the EFSA European Food Safety Authority in 2001), had expressed an opinion on the maximum tolerable intake level (hereinafter referred to as the higher level) of selenium, establishing proportionately, lower levels of intake for children, based on differences in body weight compared to adults. Based on the results in humans, the Scientific Committee on Food noted that a selenium intake of approximately 850μg/day could be considered as NOAEL for clinical selenosis. Using an uncertainty factor of 3 to take into account the remaining uncertainties in the studies, the Scientific Committee on Food calculated a higher level for selenium than 300μg/day (4). The SELECT study (Selenium and Vitamin E Cancer Prevention Trial) started in 2001 on 35,533 men provided the following results (5):

2008: In September 2008, researchers found that selenium (200μg/day) and vitamin E, taken alone or together, for an average of five and a half years, did not prevent prostate cancer.

2011: data from updated studies showed that, in men taking vitamin E, there was a 17 percent increase in the risk of prostate cancer compared to men taking placebo.

2014: the analysis showed that the men who started the process with high levels of selenium doubled the risk of developing high-grade prostate cancer for taking selenium supplements and men who had low selenium levels at the beginning of the process, they doubled the risk of high grade prostate cancer by taking vitamin E.

Scientists do not understand how these supplements really work and, above all, the interactions that these supplements have with each other or with foods, drugs, or other supplements. There are no clinical studies that show an advantage from taking vitamin E or selenium to reduce the risk of prostate cancer or any other cancer or heart disease (6).

Therefore, before taking dietary supplements containing Selenium, establish your average dietary exposure to the component. In Europe adults fluctuate around 108μg/day, while for children, between 42 and 77μg/day. The maximum thresholds are divided as follows (7):

Adults: 250μg/day

from 1 to 3 years of age, 60μg/day

from 4 to 6 years of age, 90μg/day

from 7 to 10 years of age, 130μg/day

Selenomethionine studies

Molecular Formula: C₅H₁₁NO2Se

Molecular Weight: 196.119 g/mol

CAS: 1464-42-2  2578-28-1  3211-76-5

EC Number: 215-977-0

PubChem Substance ID 329751085

MDL number MFCD00037210

Synonyms:

• Selenomethionine
• L-selenomethionine
• 2-amino-4-(methylselanyl)butanoic acid
• DL-Selenomethionine
• Seleno-DL-methionine
• Butanoic acid, 2-amino-4-(methylseleno)-
• (+-)-Selenomethionine
• 2-amino-4-(methylseleno)butanoic acid
• 2-amino-4-methylselanylbutanoic acid
• Seleno-D,L-methionine
• (S)-2-Amino-4-(methylselenyl)butyric acid
• 2-Amino-4-(methylselenyl)butyric acid

 References________________________________________

(1) Request no. EFSA-Q-2005-103, EFSA-Q-2006-195, EFSA-Q-2006-196, EFSA-Q-2006-304

(2) COMMISSION EXECUTION REGULATION (EU) No. 121/2014
of 7 February 2014
concerning the authorization of L-selenomethionine as an additive in feed intended for all animal species

(3) Impacts of feeding selenium-methionine and chromium-methionine on performance, serum components, antioxidant status, and physiological responses to transportation stress of Baluchi ewe lambs.
Mousaie A, Valizadeh R, Naserian AA, Heidarpour M, Mehrjerdi HK.
Biol Trace Elem Res. 2014 Dec; 162 (1-3): 113-23. doi: 10.1007 / s12011-014-0162-x. Epub 2014 Nov 4.
PMID: 25367352

(4) Request no. EFSA-Q-2005-103, EFSA-Q-2006-195, EFSA-Q-2006-196, EFSA-Q-2006-304

(5) http://www.cancer.gov/newscenter/qa/2008/selectqa

(6) http://www.cancer.gov/newscenter/qa/2008/selectqa
Question 14.

(7) Request no. EFSA-Q-2005-103, EFSA-Q-2006-195, EFSA-Q-2006-196, EFSA-Q-2006-304