Table 1.

Review of studies that have identified variation in microbiota profiles by sex or age group

Date	Study population	Method	Effect of sex	Effect of age	Reference
2000	Children 16 mos–7 years (n = 10), adults 21–34 years (n = 7), elderly ≥ 67 years (n = 5)	16S rRNA abundance	Not assessed	Greater abundance of Enterobacteria in children compared with adults	Hopkins et al. [4]
2006	Healthy adults between 20 and 50 years (n = 85), healthy adults, and elderly >60 years (n = 145)	Fluoresence in situ hybridization of 16S rRNA genes	Greater abundance of Bacteroides and Prevotella in males	Greater abundance of Enterobacteria in the elderly	Mueller et al. [8]
2007	Infants (n = 150), adults 25–35 years (n = 54), elderly 80–82 years (n = 45)	qPCR and fluorescence in situ hybridization of 16S rRNA genes specific for A. muciniphila	Not assessed	Decreased abundance of A. muciniphila, a type of mucin-degrading bacteria in the intestinal tract, in the elderly	Collado et al. [9]
2009	Adults 18–31 years (n = 17), institutionalized elderly 78–94 years (n = 17)	Denaturing gradient gel electrophoresis and qPCR	Not assessed	Greater abundance of Bacteroides and decreased abundance of Bifidobacteria in the elderly	Zwielehner et al. [10]
2013	Male (n = 123) and female (n = 132) nonobese diabetic germ-free and pathogen-free mice	16S rRNA gene amplicon sequencing	Intestinal communities were distinct among male and female mice	Sex-specific differences in the intestinal community were most apparent in adult mice	Markle et al. [7]