It is an inhibitor of DMBA-induced mammary tumors[1] and a "chemopreventive agent that blocks cell cycle progression and proliferation of premalignant mammary lesions and induces apoptosis of cancer cell lines in culture.

The "selenite-induced cell death could be derived from necrosis rather than apoptosis, since selenite did not significantly induce several apoptotic phenomena, including the activation of caspase-3.

[4] Methylselenocysteine is found in selenized yeast, and many vegetables: "As much as 80% of the total selenium" found in Allium species (onion, leek, garlic, ramps) Brassica species (broccoli, radish, Brussels sprouts, cabbage), and milk vetch (Astragalus species, Fabaceae) "is present as Se-methylselenocysteine."

Specifically, "It is converted via the action of β-lyase, to methylselenol and then to hydrogen selenide, which is also the key metabolite derived from" all other common forms of selenium.

But EFSA concluded that "given the absence of human studies on Se-methylselenocysteine, the relatively sparse database on the bioavailability of selenium from this source and the limited data on the safety of this source compared with other selenium compounds, the Upper Limit for selenium defined by the Scientific Committee on Food cannot be used for judging its safety.