Abstract: Objective：To investigate the difference in serum vitamin D (25-hydroxyvitamin D3) level between simple obese children and normal-weight children and the correlation between obesity and serum 25-(OH)D3.Methods：We selected 80 cases of children with simple obesity as the obesity group,who visited our hospital between December 2020 and December 2022.Additionally,we included 80 cases of normal-weight children without obesity as the control group,who visited our hospital during the same period.The obesity group included 25 cases of mild obesity,45 cases of moderate obesity,and 10 cases of severe obesity.Both groups were recorded for gender,age,height,weight and body mass index(BMI),and their serum 25-(OH)D3 levels were determined.The baseline data of two groups of children were compared and analyzed.The difference in serum 25-(OH)D3 expression levels was compared among the children with mild obesity,moderate obesity and severe obesity.Pearson′s correlation analysis was used to analyze the correlation between serum 25-(OH)D3 levels and Z-BMI in the children of the two groups.Results：The children in the obesity group had an average weight of (59.01±13.63)kg and an average BMI of 25.72±3.24.In comparison,the control group had an average weight of (41.37±12.10)kg and an average BMI of 19.26±2.42.The difference between the two groups was statistically significant (P<0.001).The average serum 25-(OH)D3 of children in the obesity group was (19.95±7.10) μg/L,which was significantly lower than the average serum 25-(OH)D3 of children in the control group,which was (29.33±6.39) μg/L (P<0.001).Among the obese children,those in the mild,moderate,and severe groups had serum 25-(OH)D3 levels of (25.25±5.51)μg/L,(19.78±8.05)μg/L,and (14.46±6.37)μg/L,respectively,and the difference among the three groups was statistically significant (P<0.001).No gender difference was found in serum 25-(OH)D3 levels among children in the three groups (P>0.05).Pearson′s correlation analysis revealed a negative correlation between serum 25-(OH)D3 levels and Z-BMI in children(r=-0.473,P<0.05).Conclusion：Serum 25-(OH)D3 levels are significantly lower in children with simple obesity than in normal-weight children,and there is a negative correlation between the degree of obesity and serum 25-(OH)D3 levels in children.Obese children should take vitamin D supplements.

Key words: Simple obesity, Vitamin D, 25-hydroxyvitamin D3, Child