Free Triiodothyronine

When low (metabolic adaptation / caloric deficit):

Supplements:

• Selenium -- 200mcg/day, supports T4-to-T3 conversion (deiodinase enzymes are selenium-dependent)
• Zinc -- 30mg/day, supports thyroid hormone metabolism
• Ashwagandha -- 300-600mg/day, may improve T4-to-T3 conversion

Lifestyle:

• Increase caloric intake -- T3 drops are the body's adaptive response to sustained deficit; reverse dieting restores T3
• Implement periodic refeeds (1-2 high-carb days/week) during contest prep to transiently boost T3
• Ensure adequate carbohydrate intake -- very low carb diets suppress T3 independently of total calories
• If on GH, this can improve T4-to-T3 conversion and partially offset prep-related T3 decline

When high (exogenous T3 / Cytomel):

• Typical contest prep dose: 25-50mcg/day; doses above 75mcg/day are catabolic even with AAS
• Taper gradually over 2-3 weeks when discontinuing (e.g., reduce by 12.5mcg every 5-7 days) to avoid rebound hypothyroidism
• Always run T3 alongside adequate AAS to prevent muscle catabolism
• Monitor resting heart rate -- persistently >90bpm suggests dose is too high

References:

• Garber, J. R., Cobin, R. H., Gharib, H., et al. (2012). Clinical practice guidelines for hypothyroidism in adults. Thyroid, 22(12), 1200-1235. DOI: 10.1089/thy.2012.0205
• Ventura, M., Melo, M., & Carrilho, F. (2017). Selenium and thyroid disease: From pathophysiology to treatment. International Journal of Endocrinology, 2017, 1297658. DOI: 10.1155/2017/1297658
• Rayman, M. P. (2012). Selenium and human health. The Lancet, 379(9822), 1256-1268. DOI: 10.1016/S0140-6736(11)61452-9