Serum vitamin D status among healthy children in Hainan, South China: a multi-center analysis of 10,262 children

Background: There are limited data regarding the prevalence and risk factors relating to vitamin D deficiency (VDD) in children of Hainan, a tropical city with abundant sunlight in China. To gather and analyze the serum VD levels of healthy children in Hainan, so as to understand their VD nutritional status and improve the representative data of VD nutritional status in South China. Methods: Children who presented to the outpatient clinic for physical examination at 4 hospitals in the Hainan Province from 2012 to 2020 were enrolled in this study. The serum 25-hydroxyvitamin D (25-OHD) levels was analyzed. 25-OHD levels <50 nmol/L is considered VDD, 50-75 nmol/L is vitamin D insufficiency (VDI), and >= 75 nmol/L is VD sufficient (VDS). Results: The average serum 25-OHD level was 94.63 +/- 49.99 nmol/L [95% confidence interval (CI): 93.67-95.60]. VDD was detected in 13.98% of participants (1,435 cases), VDI was detected in 30.60% of participants (3,140 cases), and 55.42% presented with VDS (5,687 cases). The average 25-OHD level of boys was significantly higher than that of girls (t=3.67, P<0.001). The average serum 25-OHD levels in the following age groups 0-1, 1-3, 3-7, 7-14, and 14-18 years were 105.92 +/- 57.39, 100.55 +/- 53.22, 86.35 +/- 39.19, 73.61 +/- 34.21, and 54.97 +/- 19.19 nmol/L, respectively. These results suggested that with an increase in age, the 25-OHD levels decreased. The average 25-OHD levels of children with a body mass index (BMI) <85(th) percentile were significantly higher than that of children in the overweight and obese group (F=7.393, P=0.001). Conclusions: A certain proportion of all age groups showed vitamin D deficiency and insufficiency in Hainan. A formal recommendation for vitamin D supplementation should be considered, especially in autumn and winter seasons for children over 7 years old, and in those with BMI >= 85(th) percentile or BMI >= 95(th) percentile.