Association between overweight or obesity and vitamin D status in preschool children: an epidemiological survey in Beijing, China, 2021-2023.

Background: Previous studies have shown that vitamin D deficiency is a risk factor for obesity in children and adolescents, but most focus on school-age children and adolescents, with little attention paid preschoolers.

Objectives: To explore the relationship between overweight or obesity in the context of vitamin D intake among preschool children in Beijing, and analyze the correlation.

Methods: A total of 51,640 preschoolers (26,775 boys; 24,865 girls), aged 1-6 years, were recruited for physical examination. Overweight or obesity was defined according to the World Health Organization Child Growth and Development Standards (2006 edition). Serum 25-hydroxy (OH) vitamin D levels were determined using standardized liquid chromatography-tandem mass spectrometry (LC-MS/MS), and vitamin D status was evaluated based on the Practice Guide on Clinical Issues Related to Vitamin D Nutrition in Chinese Children (2022).

Results: No significant change was observed in the incidence of overweight (7.72, 7.51, and 7.24 %) or obesity (2.75, 2.63, and 2.40 %) from 2021 to 2023. Among boys, 7.3 % were overweight and 2.8 % were obese. Among girls, 7.6 % were overweight and 2.3 % were obese. Vitamin D deficiency (2.10, 1.70, and 1.01 %) and insufficiency rate (24.09, 18.42, and 15.44 %) showed a decreasing trend. Deficiency or insufficiency was most common in children aged 36-59 months, and serum 25- (OH) vitamin D levels were significantly lower in winter compared to other seasons, with the highest levels in summer. Time spent outdoors was significantly less among children with vitamin D deficiency or insufficiency, and preschoolers who spent more than 2.94 h/day had higher serum vitamin D level. Serum 25- (OH) vitamin D levels were negatively correlated with body mass index (BMI), with overweight or obesity preschoolers showing significantly lower than their normal weight group. After adjusting for age, gender and season, family economic status, guardian educational level and time spent outdoors, the odds of vitamin D deficiency and insufficiency in overweight or obesity in preschoolers were 1.025 (95 % Cl: 1.002-1.174), 1.218 (95 % Cl: 1.099-1.708), respectively.

Conclusions: From 2021 to 2023, there was no significant change in the incidence of overweight or obesity among preschool children in Beijing. Furthermore, the rate of vitamin D deficiency or insufficiency decreased year by year. Vitamin D deficiency or insufficiency associates with factors such as age, season of the year, and time spent outdoors, and there is an association between overweight or obesity and vitamin D status among preschoolers.