Selenium is incorporated into 25 selenoproteins that are structurally integrated into human tissues, including the thyroid, immune cells, and cell membranes.

Study: Selenomethionine as a dual-mechanism ferroptosis inhibitor: selenium-supply-driven GPX4 biosynthesis beyond transsulfuration and reductive-capacity-mediated ROS scavenging independent of GPX4 activity

This study shows that selenium is used by the body to build a key protein (GPX4) that protects cells from damage — proving selenium becomes part of human proteins in tissues like the kidney. This supports the idea that selenium is built into important proteins in the body.

Study: Selenoproteins: molecular pathways and physiological roles.

Selenium is used by the body to build 25 special proteins that are built into important parts like the thyroid, immune cells, and cell membranes — and this study confirms those proteins exist and do vital jobs in those places.

Study: From selenium to sulfur: predictive modeling unveils conformational and bonding changes in selenoproteins.

This study used computers to map out the shapes of 25 human proteins that contain selenium, and it found that selenium is indeed part of their structure — just like the claim says. Even when selenium was swapped out, most proteins still held their shape, but that doesn’t mean selenium wasn’t originally there.