Objective To investigate serum vitamin D levels of healthy children in Beijing and to analyze the factors affecting vitamin D level.Methods Healthy children aged 1-14 years old who underwent physical examination in department of pediatrica,Civil Aviation General Hospital from September 2016 to September 2020 were randomly selected as research objects.Clinical data of the children were collected and a questionnaires survey was conducted.The level of 25-hydroxy vitamin D[25-(OH)D]was detected by liquid chromatography-tandem mass spectrometry.Serum 25-(OH)D levels were compared between different groups(grouped by age,gender,season,outdoor activity time,and vitamin D supplementation).Results A total of 990 children met the inclusion criteria.There were 500 boys and 490 girls,with a mean age of(6.42±3.50)years old.The mean serum level of 25-(OH)D was(28.23±6.74)ng/ml in all the selected children(range,11.70-51.90 ng/ml),(31.99±6.47)ng/ml in young child group,(27.54±6.49)ng/ml in preschool group,and(25.84±5.93)ng/ml in school-age group.The serum level of 25-(OH)D in the young child group was significantly higher than those in the preschool group and school-age group(P<0.05).There was no significant difference in the serum level of 25-(OH)D between the preschool group and school-age group(P>0.05).There were significant differences in the proportions of children with normal 25-(OH)D,insufficient 25-(OH)D and deficient 25-(OH)D among different age groups(P<0.05).There was no significant difference in the serum level of 25-(OH)D between boys and girls in the same age group(P>0.05).There was significant difference in 25-(OH)D levels among different age groups with a same gender(P<0.05).There was no significant difference in the proportions of children with normal 25-(OH)D,insufficient 25-(OH)D,or deficient 25-(OH)D between boys and girls(P>0.05).The level of serum 25-(OH)D and the proportion of children with normal serum 25-(OH)D reached the highest in summer and the lowest in winter.There were significant differences in the serum 25-(OH)D levels and the proportion of children with normal serum 25-(OH)D among different seasons(P<0.05).The serum 25-(OH)D level in children with outdoor activities≥1 h daily was significantly higher than that in children with outdoor activities<1 h daily(P<0.05).There were significant differences in the proportions of normal 25-(OH)D,insufficient 25-(OH)D and deficient 25-(OH)D between children with outdoor activities≥1 h daily and children with outdoor activities<1 h daily(P<0.05).The serum levels of 25-(OH)D in children of never-supplement group and sometimes-supplement group were lower than that in the daily supplement group(P<0.05),and there were significant differences in the proportions of normal 25-(OH)D,insufficient 25-(OH)D and deficient 25-(OH)D among the three groups(P<0.05).Conclusion Vitamin D nutritional status of healthy children in Beijing is good.Serum 25-(OH)D level decreases with age.No difference is found in the serum 25-(OH)D level between boys and girls in every age group.No abnormal vitamin D level is found in young children.The insufficiency and deficiency of vitamin D exist in preschool and school-age children,which needs to be improved.Vitamin D level in children is related to seasons.Sufficient time of outdoor activities and regular supplementation of vitamin D can help improve vitamin D nutritional status in children.

Objective To understand the level of vitamin A (VA)in children in Beijing city.Methods 292 children aged from 0~14 years old visited the health clinic from November 2012 to March 2013 in Beijing city were surveyed by a question-naire,and medical history,physical examination,a blood sample was collected from each child,and serum VA was measured with reversed-phase high-performance liquid chromatography(HPLC).Results ①The mean serum VA concentration for the 292 children was (1.09 ± 0.29)μmol/L.②There were 5.8% (17/292)of children affected with subclinical VAD (SVAD),and 38.0% (107/292)had suspected SVAD (SSVAD).③Multivariate logistic regression analysis showed that parents were unware of health implications of VA,low VA intake and recurrent respiratory infection were associated with SVAD or SSVAD.Conclusion Low VA status remains a nutritional problem in children in Beij ing city.Multiple factors need to be considered together for them,such as parents were unware of health implications of VA,low VA intake and re-current respiratory infection.