Objective: The present study aimed to (i) evaluate the reproducibility and validity of a designed FFQ, (ii) apply the FFQ for estimating the dietary intakes of four flavonols and two flavones in female adolescents and (iii) explain their major dietary sources. Design: The reproducibility between the first and second FFQ administrations (1 year interval) was estimated using the intra-class correlation coefficient. The validity of the first FFQ relative to the average of four three-day 24 h dietary recalls (24-HR) from four seasons was assessed using the Spearman correlation coefficient. Using a flavonoid content database, the individual flavonol and flavone intakes were calculated and the major food sources were estimated. Setting: Middle school in Suihua area of Heilongjiang Province, northern China. Subjects: Female adolescents (n 887) aged 12-18 years. Results: Better reproducibility and validity were obtained in the present study. The flavonol and flavone intakes were 16·29 and 4·31 mg/d, respectively. Quercetin and kaempferol were the major contributors (26·8 % and 23·7 %, respectively) to the total intake of flavonols and flavones. The main food sources of flavonols and flavones were apples (14·1 %), followed by potatoes (7·5 %), lettuce (7·3 %) and oranges (7·3 %). Conclusions: The dietary flavonol and flavone intakes among female adolescents in northern China were similar to those reported in several countries, but significant differences were observed in the food sources ascribed to the geographical location and dietary characteristics.

Background Living at high latitudes is one of the risk factors for vitamin D deficiency in children. However, evidence on vitamin D improvement for this pediatric population to date is limited. This study aims at evaluating the effect of different supplementation methods and outdoor activity time on the vitamin D status of children in North China. Methods A total of 55,925 children aged 1 month to 18 years old were recruited from pediatric outpatient departments from July 2016 to June 2017. Data on demographics, anthropometric measurements, vitamin D supplementation, and outdoor time were recorded. The serum levels of 25-hydroxycholecalciferol (25(OH)D) were determined by high performance liquid chromatography tandem–mass spectrometry. Logistic regression analysis was performed to assess the association of vitamin D supplementation or outdoor time with blood vitamin D status, adjusted for age, gender, BMI for age, and seasons. Results The overall rate of hypovitaminosis D was 65.60%. Of the children’s outdoor time, 35.63%, 31.95%, and 32.42% were below 30 min/d, 30–60 min/d and over 60 min/d, respectively. Furthermore, the proportion of iatrogenic supplementation, voluntary supplementation and no vitamin D supplementation among the children was 16.48%, 32.87%, and 50.65%, respectively. After adjusted for confounding factors, vitamin D supplementation was associated with a lower risk of hypovitaminosis D, with OR (95% CI) of 0.191 (0.180, 0.202) in children with iatrogenic supplementation and 0.423 (0.404, 0.443) in those with voluntary supplementation, compared with children without vitamin D supplementation. In addition, longer outdoor time was associated with a lower risk of hypovitaminosis D [0.479 (0.456, 0.504) for 60 min/d, 0.737 (0.701, 0.776) for 30–60 min/d], independent of vitamin D supplementation. Conclusions High prevalence of vitamin D deficiency was found in children living at high latitudes. Vitamin D supplementation and outdoor time are all negatively associated with children’s vitamin D deficiency. Routine 25(OH)D testing combined with vitamin D supplementation might be an effective approach to prevent hypovitaminosis D among children living at high latitudes.

Background: Living at high latitudes is one of the risk factors for vitamin D deficiency in children. However, evidence on vitamin D improvement for this pediatric population to date is limited. This study aims at evaluating the effect of different vitamin D intervention methods and outdoor activity on the vitamin D status of children in North China. Methods: A total of 55,925 children aged 1 month to 18 years old were recruited from pediatric outpatient departments from July 2016 to June 2017. Data on demographics, anthropometric measurements, vitamin D intervention, and outdoor activity were recorded. The serum levels of 25-hydroxycholecalciferol (25(OH)D) were determined by high performance liquid chromatography tandem–mass spectrometry. Logistic regression analysis was performed to assess the association of vitamin D intervention or outdoor activity with blood vitamin D status, adjusted for age, gender, BMI for age, and seasons.Results: The overall rate of hypovitaminosis D was 65.60%. Of the children’s outdoor activity, 35.63%, 31.95%, and 32.42% were below 30min/d, 30-60 min/d and over 60min/d, respectively. Furthermore, the proportion of therapeutic intervention, supplementation intervention and no vitamin D intervention among the children was 16.48%, 32.87%, and 50.65%, respectively. After adjusted for confounding factors, vitamin D intervention was associated with a lower risk of hypovitaminosis D, with OR (95% CI) of 0.191 (0.180, 0.202) in children with therapeutic doses and 0.423 (0.404, 0.443) in those with supplementation doses, compared with children without vitamin D intervention. In addition, longer outdoor time was associated with a lower risk of hypovitaminosis D [0.479 (0.456, 0.504) for 60 min/d, 0.737 (0.701, 0.776) for 30–60 min/d], independent of vitamin D intervention. Conclusions: High prevalence of vitamin D deficiency was found in children living at high latitudes. Vitamin D intervention and outdoor activity are all negatively associated with children’s vitamin D deficiency. Routine vitamin D intervention combined with increased outdoor time might be an effective approach to prevent hypovitaminosis D among children, especially those at school, living at high latitudes.