BackgroundEnvironmental enteric dysfunction (EED) is an acquired, subclinical state of intestinal inflammation common in children and adults in low- and middle-income countries. Although vitamin D3 supplementation has purported anti-inflammatory properties, its ability to ameliorate biomarkers of EED remains unclear. ObjectiveTo examine the effects of maternal vitamin D3 supplementation during pregnancy and lactation on biomarkers of EED, systemic inflammation, and growth in women living with HIV and their infants in Dar es Salaam, Tanzania. MethodsWe conducted subgroup analyses among randomly selected mothers (n=720) and infants (n=365 at six weeks of age, and n=266 at six months of age) that participated in a randomized, triple-blind, placebo-controlled trial of daily maternal 3,000 IU vitamin D3 supplementation from the second trimester of pregnancy until one year postpartum. Biomarkers of EED [soluble CD14 and intestinal fatty acid-binding protein (I-FABP)], systemic inflammation [C-reactive protein and alpha-1-acid glycoprotein (AGP)], and growth factors [insulin-like growth factor-1 (IGF-1) and fibroblast growth factor 21] were measured via the Micronutrient and Environmental Enteric Dysfunction Assessment Tool. Anti-flagellin and anti-lipopolysaccharide immunoglobulins were measured via enzyme-linked immunosorbent assay. Comparisons by randomized treatment arm were performed using ordinary least squared regression models with log2-transformed biomarkers. ResultsAt 32 weeks gestation, I-FABP (β: -0.19, p = 0.03) and AGP (β: -0.11, p = 0.04) were significantly lower in mothers in the vitamin D3 group compared to the placebo group. At six weeks of age, IGF-1 (β: -0.31, p = 0.03) was significantly lower in infants whose mothers were in the vitamin D3 group compared to the placebo group. ConclusionsVitamin D3 supplementation during pregnancy and lactation reduced selected EED and systemic inflammation biomarkers among women living with HIV. While the effects of maternal vitamin D3 supplementation do not appear to extend to infants, there may be an effect on growth factors. Clinical Trial RegistryClinicalTrials.gov identifier for parent trial: NCT02305927 (https://clinicaltrials.gov/study/NCT02305927)