Objective     To investigate the status and deficiency of 25-hydroxy vitamin D [25-(OH)D] in left-behind children at 3～6 years old living in Yongchuan District

Chongqing

and to explore the correlation of vitamin D receptor (VDR) genetic polymorphism FOK Ⅰ and serum levels of 25-(OH)D3. Methods      A total of 285 left-behind children at the age of 3 to 6 living in some towns of Yongchuan District were recruited in our hospital during November 2015 to April 2016. They all took physical examination

and their serum level of 25-(OH)D was detected by liquid chromatography-tandem mass spectrometry. The genotypes of FOK Ⅰ polymorphisms for VDR gene were analyzed with polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). Results      ① The average serum level of 25-(OH)D was 19.566±5.185 ng/mL in the 285 children

with 8 cases (2.81%) sufficient

118 cases (41.40%) insufficient

151 cases (52.98%) deficient and 8 cases (2.81%) severely deficient. The level was lower in the leftbehind children than the non-left-behind children

though no statistical difference. The level was the highest in the 3-yea-old group

and statistical differences were observed among the different age groups (P0.001). ② The serum level of 25-(OH)D was lower in the children with ff genotype than those with Ff and FF genotypes

but there was no statistical difference among different genotypes groups (P0.05). Covariance analysis indicated that there was no statistical difference in the serum level of 25-(OH)D among the different genotypes groups after adjustment of age (P0.05). Conclusion      The serum level of 25-(OH)D is severely low in the left-behind children at the age of 3 to 6 in Yongchuan District. Some measures should be implied to improve the levels. Fok I polymorphisms in VDR gene might have no correlation with the serum level of 25-(OH)D.