AMPK	AMP-activated protein kinase
D1/D2/D3	Deiodinase types 1, 2, and 3 (protein level)
DIO1/DIO2/DIO3	Deiodinase isoforms 1, 2, and 3 (gene level)
ΔΨm	Mitochondrial membrane potential
FOXO3a	Forkhead box O3a
fT3	Free triiodothyronine
fT4	Free thyroxine
FXR	Farnesoid X receptor
GPx	Glutathione peroxidase
HPT axis	Hypothalamic–pituitary–thyroid axis
HRV	Heart rate variability
IL-6	Interleukin-6
LPS	Lipopolysaccharides
MCT8	Monocarboxylate transporter 8
MTHFR	Methylenetetrahydrofolate reductase
NAD+/NADH	Nicotinamide adenine dinucleotide (oxidized/reduced forms)
NRF1	Nuclear respiratory factor 1
NRF2	Nuclear respiratory factor 2
NTIS	Non-thyroidal illness syndrome
OXPHOS	Oxidative phosphorylation
PGC-1α	Peroxisome proliferator–activated receptor gamma coactivator 1-alpha
RED-S	Relative Energy Deficiency in Sport
ROS	Reactive oxygen species
rT3	Reverse triiodothyronine
rT4	Reverse thyroxine
SCFA	Short-chain fatty acids
SIRT1	Sirtuin-1
SOD2	Superoxide dismutase 2
T2	3,5-diiodo-L-thyronine
T3	Triiodothyronine
T4	Thyroxine
TGR5	Takeda G-protein-coupled receptor 5
THs	Thyroid hormones
THRs	Thyroid hormone receptors
TFAM	Mitochondrial transcription factor A
TLR4	Toll-like receptor 4
TMAO	Trimethylamine-N-oxide
TNF-α	Tumour necrosis factor alpha
TRH	Thyrotropin-releasing hormone
TSH	Thyroid-stimulating hormone
UCP2	Uncoupling protein 2
UCP3	Uncoupling protein 3
UCPs	Uncoupling proteins
VDR	Vitamin D receptor