Table 2. Association between estrogen and the bacterial composition and diversity.

Summary of findings from the included studies (n=6) that investigated the effect of estrogen on the bacterial composition and/or diversity. Three of these studies investigated the effect of estrogen on both composition and diversity, whilst the remaining studies explored its effect on either composition (n=1) or diversity (n=2) alone.

N/A: not applicable; BMD: bone mineral density.

Study	Estrogen
	Bacterial Composition	Bacterial Diversity
Flores et al.(23)	↑ Clostridia taxa including Ruminococcaceae Oscillibacter, Ruminococcaceae Subdoligranulum Ruminococcaceae genus NA and non-Clostridiales in men and post-menopausal women	↑ Alpha diversity in men and post-menopausal women ↔ Alpha diversity in pre-menopausal women ↔Beta diversity between groups
Fuhrman et al.(24)	↑ Clostridiales order and in particular the Ruminococcaceae family and the Ruminococcus genus in healthy women ↓ Bacteroides genus in healthy women	↑ Alpha diversity in healthy post-menopausal women
Goedert et al.(21)	N/A	↑ Alpha diversity in healthy post-menopausal women ↔ Alpha diversity in women with breast cancer
Goedert et al.(22)	N/A	↑ Alpha diversity for the IgA-negative microbiota in women (control group)
He et al.(26)	↔ In a cohort of women with normal BMD, osteopenia and osteoporosis	↔ Alpha diversity in a cohort of women with normal BMD, osteopenia and osteoporosis
Zengul et al.(32)	↔ Any bacterial species in post-menopausal women with breast cancer	N/A

^*↑ denotes a positive association between the sex hormone and the outcome of interest.

^*↓ denotes a negative/inverse association between the sex hormone and the outcome of interest.

^*↔ denotes a lack of association found between the sex hormone and the outcome of interest