Hormonal
Short-term thyroxine (T4) supplementation (200 mg/day for 3 days) in healthy euthyroid males reduces skeletal muscle mitochondrial efficiency (state 3 respiration and RCR) by approximately 30% without altering ATP demand or exercise efficiency.
Taking T4 (thyroxine) for 3 days at a dose of 200 mg/day in healthy men does not improve exercise efficiency or resting metabolic rate significantly. However, it does reduce the efficiency of skeletal muscle mitochondria, meaning the muscles become less effective at producing ATP. This suggests that T4 supplementation in healthy individuals may impair mitochondrial function without providing metabolic or performance benefits.
The maximal capacity to produce ATP (state 3 respiration) and the coupled state of the mitochondria (RCR) were reduced by approximately 30% with T4 (p = 0.057 and p = 0.04, respectively).
Why this rating
Small sample size (n=10), short duration (3 days), and mixed statistical significance (p=0.057 for state 3, p=0.04 for RCR).
Source
Effect of Short-Term Thyroxine Administration on Energy Metabolism and Mitochondrial Efficiency in Humans
Darcy L. Johannsen et al. · PLoS ONE · 2012
DOI 10.1371/journal.pone.0040837
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