This study was performed to estimate the prevalence of vitamin D status in middle school students and to identify the relationship with many related factors including general characteristic, anthropometry, hematological index, daily nutrient intakes, dietary & health-related behaviors. The participants in this study were total 91 students (boys 44, girls 47) in middle school students in Gyeongnam. The results are summarized as follows :
1. The mean concentration of 25(OH)D in girls was significantly lower than in boys, 16.1 ± 4.57 ng/mL for boys vs. 13.5 ± 2.89 ng/mL for girls (p < 0.05). In our total sample of 91 subjects, 0.0% had optimal concentrations of 25(OH)D (> 30 ng/mL) and 9.9% had 25(OH)D insufficiency (21 ? 29 ng/mL) and 90.1% had deficient level (< 20 ng/mL). 100 % of boys and girls showed vitamin D insufficiency or deficiency.
2. How to go to school (p < 0.05), frequency of applying sunscreen (p < 0.01) and hours of using smart-device were showed significant difference among boys and girls (p < 0.01). In the boys, mean concentration of 25(OH)D was significantly higher in the order of ''apartment'' (17.5 ng/mL) > ''villa'' (15.1 ng/mL) > ''single house'' (11.7 ng/mL)(p < 0.01). In the girls, mean concentration of 25(OH)D was significantly higher in the order of ''bike'' (14.5 ng/mL) > ''bus or car'' (12.8 ng/mL) > ''walking'' (11.0 ng/mL)(p < 0.01).
3. The height and weight were significantly higher in boys (165.3 ± 5.0 cm, 61.1 ± 13.8 kg) than girls (159.4 ± 5.1 cm, 53.2 ± 6.5 kg) (p <0.001).
4. Hemoglobin (p < 0.001), hematocrit (p < 0.001), glucose (p < 0.05) and P (p < 0.01) levels were significantly higher in boys than girls. Triglyceride level(p < 0.05) was significantly higher in girls than boys.
5. In the daily nutrient intakes, intakes of energy (p < 0.001), carbohydrate (p < 0.001), lipid (p < 0.01), protein (p < 0.001), vitamin B2 (p < 0.001), niacin (p < 0.001), vitamin B6 (p < 0.001), vitamin B12 (p < 0.05), Ca (p < 0.001) and P (p < 0.01) were significantly higher in boys than girls. While intakes of vitamin A (p < 0.001), vitamin E (p < 0.001), vitamin K (p < 0.05), folate (p < 0.001) and cholesterol (p < 0.01) were significantly higher in girls than boys.
6. The nutrient adequacy ratio (NAR) of vitamin A was significantly higher in girls than boys (p < 0.01). While the NAR of vitamin B?, Ca, P was significantly higher in boys than girls (p < 0.01).
7. In the dietary & health-related behaviors, frequency of having breakfast was significantly higher in boys than girls (p < 0.01).
8. In the nutritional knowledge, the percentage of correct answers in ''high nutritious food is high calorie food'' was significantly higher in girls than boys (p < 0.05). While the percentage of correct answers in ‘When calcium intake is low, it is taller’ was significantly higher in boys than girls (p < 0.05).
9. In the boys, Serum 25(OH)D levels were negatively correlated with hours of using smart-device(p < 0.01). In the girls, serum 25(OH)D levels were positively correlated with time to go to school(p < 0.05) and were negatively correlated with frequency of applying sunscreen(p < 0.01).
10. In the boys, serum 25(OH)D levels were negatively correlated with hemoglobin (p < 0.001), hematocrit(p < 0.001) and systolic blood pressure (p < 0.01). In the girls, serum 25(OH)D levels were positively correlated with total protein and Ca levels (p < 0.01).
11. In the boys, serum 25(OH)D levels were positively correlated with intakes of protein, vitamin K, folate and P (p < 0.05).
The results of this study showed that vitamin D insufficiency or deficiency is very common health problem among young adolescents in Korea. Therefore, public health interventions such as outdoor activity and vitamin D supplementation may be needed to improve vitamin D status in adolescents.