Is FT3 useful for Sport?

The DIO2 Thr92Ala variant (rs225014) has been associated in population studies with slightly altered deiodinase-2 activity, which may affect conversion of T4 to active T3. However, the effect size is small, and clinical relevance for athletes remains unclear. A direct need for extra iodine or selenium cannot be inferred from this genotype alone. Both micronutrients are essential for thyroid function, but supplementation without prior lab testing (TSH, fT3, fT4, selenium status) is not evidence-based and may be risky in excess (e.g., iodine in autoimmune thyroiditis). For athletes aiming to optimize metabolism, the thyroid axis should be assessed via blood markers before deriving supplement recommendations. MyBody-X DNA tests provide indications, not clinical diagnoses. The evidence for personalized supplementation based on DIO2 is currently mechanistic.