Low Dietary Vitamin D since Pre‐mating Does not Modify Fecal <i>Bacteroides</i> Counts of Mouse Dams at the End of Pregnancy

Rationale Pioneering data suggested that micronutrients, including vitamin D, affect gut microbiota composition. This may be particularly relevant during pregnancy, since vitamin D supplementation is a common strategy worldwide to support health of the mother and her fetus. Alteration of the gut microbiota during pregnancy may affect gut microbial colonization of the newborn via vertical transfer (mother to offspring) of mother‐derived microorganisms and hence have long‐lasting effects to offspring health. The objective of this study was to determine if altering the level of dietary vitamin D affects the counts of Bacteroides , representing a main Gram‐negative genus in the gut microbiota, in the feces of dams prior to delivery. Study Design & Methods 3‐week old female C57BL/6J mice were fed AIN‐93G diet containing either 25 (low, LD) or 5000 (high, HD) IU vitamin D/kg diet (significantly below and above the 1000 IU vitamin D/kg of the reference AIN‐93G diet) for 4 weeks before mating until the end of lactation (age 13 weeks). Body weight was assessed at mating and weaning. Freshly passed fecal samples were collected just before mating (n=3–6), 1 week post‐mating (n=3–6), and before birth (n=19–20), and used for DNA extraction and quantification of Bacteroides using genus‐specific primers by quantitative PCR. Counts were normalized to total bacteria. Results There was no difference in body weight at mating ( p = 0.771) nor in body weight gain throughout pregnancy and lactation between the groups ( p = 0.238). Percent of fecal Bacteroides normalized to total bacteria increased over time and peaked before birth, independent of the vitamin D intervention (Diet: 0.402, Time: 0.003, Interaction: 0.508). There were no differences in percent Bacteroides normalized to total bacteria between dams receiving high or low vitamin D at the end of pregnancy (LD: 9.10 ± 2.01%, HD: 14.15 ± 2.85%; p = 0.153). Conclusion Bacteroides belong to the core microbiome and are largely saccharolytic. Their increase throughout pregnancy may modify the relationship between microbiota and energy metabolism in the mother and thus her offspring, besides affecting colonization of the offspring. While vitamin D impacts murine microbiota in health and colitis models, here, two substantially different levels of dietary vitamin D did not affect fecal Bacteroides variation during pregnancy. This suggests that Bacteroides are not susceptible to dietary vitamin D or that its effects are masked by other factors in this context. Studies of the whole microbiome at various intestinal regions will help understand this relationship. Support or Funding Information ‐Centrum Foundation Pfizer Consumer Healthcare Research Innovation Fund and the Department of Nutritional Sciences at the University of Toronto to WEW and EMC. ‐NSERC Discovery Grant to EMC. ‐Christopher R. Villa was partially funded by the Banting and Best Diabetes Centre‐Novo Nordisk Studentship and ‐Tamarack Graduate Award in Diabetes Research and by an Ontario Graduate Scholarship. ‐Wendy Ward holds a Canada Research Chair in Bone and Muscle Development. ‐Elena Comelli holds the Lawson Family Chair in Microbiome Nutrition Research at the University of Toronto.

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