Table 1.

Microbial changes related to subclinical and overt hypothyroidism, and the relation of the altered microbiota to metabolic diseases.

Thyroid disorder (Ref)	Method of evaluation	Changes in gut microbiota compared to control	Microbial functions	Microorganism also related to metabolic diseases	References
Subclinical Hypothyroidism (203)	Male/Female stools, 16S rDNA V3-V4 regions sequenced with Illumina Hiseq PE250 platform	Increased relative abundance of the genera Odoribacter and Enterococcus in high and middle dosage of L-thyroxine.	-Starch and glucose metabolism, production of isobutyric and isovaleric acid: Some Odoribacter species -Production of acetate: Enterococcus species -Potential opportunistic pathogens. Genera Odoribacter, and Enterococcus.	-Individuals with Hypercholesterolemia ­Odoribacter.	(237, 238)
Subclinical hypothyroidism in pregnant women (236)	Pregnant women stools, 16S rRNA V3-V4 regions sequenced with Illumina NovaSeq platform.	Subclinical Hypothyroidism pregnant women (20-23+6 weeks) * TPOAb- patients: Increased abundance of ­Prevotella * TPOAb+ LT4 - patients: Increased abundance of ­Prevotella and reduced Gammaproteobacteria, Enterobacteriaceae * TPOAb+ ${\text{LT}}_4^{+}$ patients: Reduced abundance of Bacteroidia and Prevotella. Subclinical Hypothyroidism pregnant (28-33+6 weeks) * TPOAb- patients: Increased abundance of ­Blautia and Agathobacter genera. Reduced abundance of Dorea formicigenerans and Bifidobacterium longum * TPOAb+ LT4 - patients: Increased abundance of ­Blautia, and Agathobacter. Reduced abundance of Actinobacteriota, Coriobacteriia, Actinobacteria, Bifidobacterium, Dorea formicigenerans, and Bifidobacterium longum * TPOAb+ LT4 + patients: Increased abundance of ­Blautia, Agathobacter, Streptococcus salivarius, and Bifidobacterium longum.	-High fiber utilizing capacity compared to Bacteroides. Prevotella. -Propionate production: Bacteroides, and B. longun. -Acetate production: Some Blautia species -Butyrate production: Agathobacter.	-Related to T1D: ¯Bifidobacterium ­ Streptococcus -Related to T2D: ­Prevotella -Related to insulin resistance ­Prevotella -Related to protective function against Bacteroides-induced glucose intolerance: ­Prevotella -Related to visceral fat accumulation: ­Blautia -Inflammatory and metabolic regulation: ­Streptococcus salivarius.	(18, 239–248)
Hypothyroidism in pregnant women (235)	Pregnant women saliva and stools, 16S rRNA V3-V4 regions sequenced with Illumina Hiseq 2500.	Oral microbiota Increased ­Gammaproteobacteria class, Streptococcus, Neisseria, Prevotella and Pasteurellaceae. Intestinal microbiota Increased abundance of ­Roseburia, Pasteurellales, Lachnospira, Prevotella, and Parabacteroides.	-Butyrate production: Roseburia -Acetate production: Prevotella	-Related to Weight gain: ­Gammaproteobacteria, Pasteurellaceae in the oral cavity and Porphyromonadaceae in the intestine. -Related to non-alcoholic fatty liver disease: ­Gammaproteobacteria and prevotella - Related to increased body mass index ­Prevotella in saliva.	(249–252)
Hypothyroidism in pregnant women (234)	Pregnant women stools, 16S rRNA V3-V4 regions, sequenced with Illumina MiSeq platform, and lipid profile determination by LC-MS.	Increased abundance of ­Prevotella and Haemophilus Reduced abundance of Blautia	-Acetate production: Some Blautia species	-Related to plasmatic levels of phosphatidylcholine and sphingomyelin ¯Blautia -Might participate in promotion of chronic inflammation: ­Prevotella strains. -Some strains related to high fecal SCFAs, obesity and cardiometabolic risk: ­Haemophilus	(131, 253, 254)