Why does peripheral tissue T3 production decrease in patients with chronic selenium deficiency?

💡 Explanation

Peripheral tissues convert T4 to T3 via deiodinases, which are selenium-dependent enzymes. Selenium deficiency reduces the activity of these enzymes, because the synthesis of deiodinases requires selenium. Therefore, T3 production decreases, rather than increases in iodine uptake or changes in TSH sensitivity.

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