Why does thyroxine (T4) to triiodothyronine (T3) conversion increase in peripheral tissues during chronic selenium deficiency?

💡 Explanation

Selenium is a cofactor for deiodinase enzymes that convert T4 to the more active T3. Because selenium deficiency impairs deiodinase activity in the thyroid gland itself, peripheral tissues compensate by increasing their own T4 to T3 conversion; therefore, the body attempts to maintain T3 levels in the face of reduced central conversion, rather than decreasing T4 synthesis directly.

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