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Purpose: Individuals with vitamin D (VD) insufficiency have a greater tendency to develop obesity and have increased systemic inflammation. Gut microbiota are involved in the regulation of host inflammation and energy metabolism, which plays a role in the pathogenesis of obesity. Thus, we aimed to evaluate the effects of different doses of VD3 on body weight, serum lipids, inflammatory factors, and intestinal barrier function in obese mice and to explore the regulatory effect of VD3 on gut microbiota in obese mice. Methods: Male C57BL/6 J mice received a normal chow diet (NCD, 10% fat) or high-fat diet (HFD, 60% fat) to induce obesity within 10 weeks. Then, HFD mice were supplemented with 5650, 8475, or 11,300 IU VD3/kg diet for 8 weeks. Finally, 16 s rRNA analysis was performed to analyze gut microbiota composition in cecal contents. In addition, body weight, serum lipids, inflammatory factors, and intestinal barrier function were analyzed. Results: VD3 supplementation reduced body weight and the levels of TG, TC, HDL-C, TNF-α, IL-1β and LPS, and increased ZO-1 in HFD-fed mice. Moreover, it increased α-diversity, reduced F/B ratio and altered microbiota composition by increasing relative abundance of Bacteroidetes, Proteobacteria, Desulfovibrio, Dehalobacterium, Odoribacter, and Parabacteroides and reducing relative abundance of Firmicutes and Ruminococcus. There were significant differences between HFD and NCD groups in several metabolic pathways, including endotoxin biosynthesis, tricarboxylic acid cycle, lipid synthesis and metabolism, and glycolysis. Conclusions: Low, medium, and high doses of VD3 inhibited weight gain, reduced levels of blood lipids and inflammatory factors, and improved endotoxemia and gut barrier function in obese mice. It also increased the α-diversity of gut microbiota in obese mice and reduced the relative abundance of some intestinal pathogenic bacteria, increased the relative abundance of some beneficial bacteria, and corrected the intestinal flora disorder of obese mice, with the low- and high-dose groups showing better effects than the medium-dose group. [ABSTRACT FROM AUTHOR]

Vitamin D‐regulating action of PPARγ on obesity has been confirmed on adipocyte differentiation. However, it is not clear whether vitamin D affects the morphological size of mature adipocytes by influencing the expression of PPARγ in vivo. Our hypothesis was that Vitamin D3 (VitD3) inhibits the growth of adipocyte size by suppressing PPARγ expression in white adipocytes of obese mice. Five‐week‐old male C57BL/6J mice were randomly divided into normal diet and high‐fat diet groups. After 10 weeks, the body weight between the two groups differed by 26.91%. The obese mice were randomly divided into a high‐fat diet, solvent control, low‐dose VitD3 (5000 IU/kg·food), medium‐dose VitD3 (7500 IU/kg·food), high‐dose VitD3 (10,000 IU/kg·food), and PPAR γ antagonist group, and the intervention lasted for 8 weeks. Diet‐induced obesity (DIO) mice fed high‐dose VitD3 exacerbated markers of adiposity (body weight, fat mass, fat mass rate, size of white and brown adipocytes, mRNA, and protein levels of ATGL and Fsp27), and the protein level of ATGL and Fsp27 decreased in the low‐dose group. In conclusion, high‐dose VitD3 possibly via inhibiting the ATGL expression, thereby inhibiting lipolysis, increasing the volume of adipocytes, and decreasing their fat‐storing ability resulted in decreased Fsp27 expression. Therefore, long‐term high‐dose oral VitD3 may not necessarily improve obesity, and we need more clinical trials to explore the intervention dose and duration of VitD3 in the treatment of VitD3 deficiency in obese patients. [ABSTRACT FROM AUTHOR]