Fig. 3

Females have lower intestinal barrier integrity. Noninvasive biomarkers of intestinal barrier function showed (A) higher circulating zonulin in females, indicative of increased intestinal barrier permeability. No age-associated changes in zonulin were observed when categorized as young adults (20–35 years of age), adults (36–65 years of age), and older adults (> 65 years of age) (B) Assessment of the human host defense peptide hCAP18/LL-37 showed lower circulating hCAP18/LL-37 in females as compared to males, which was age independent. (C) There were no age or sex differences in circulating I-FABP. (D) Circulating LPS increased with age, driven by an increase in females only. (E) Circulating kynurenine increased with age in females. (F) There were no age- or sex-associated changes in circulating tryptophan levels. (G) The ratio of kynurenine to tryptophan increased with age in both biological sexes. Statistical significance was assessed by a two-way ANOVA (A-C top), Student’s t test (A-C bottom) and simple linear regression (D-G). Data is shown as a dot for each participant. Subjects are color coded according to their biological sex. **P ≤ 0.01