Seasonal vitamin D status of healthy schoolchildren and predictors of low vitamin D status.
OBJECTIVE
The aim of the study was to assess seasonal prevalence of vitamin D deficiency according to sex and to determine the relations between serum levels of 25-hydroxyvitamin D [25(OH)D] and parathyroid hormone (PTH) and sociodemographic characteristics in otherwise healthy schoolchildren during spring and autumn.


METHODS
In a cross-sectional study, 746 healthy students aged between 11 and 18 years were recruited during spring (n = 375) and autumn (n = 371). Sociodemographic data were collected by a questionnaire. Serum 25(OH)D, PTH, calcium, phosphate, and alkaline phosphatase were measured. Serum 25(OH)D levels were categorized as <50 nmol/L (vitamin D deficiency) and <25 nmol/L (severe deficiency).


RESULTS
Mean ± standard deviation 25(OH)D levels were 22.3 ± 10.5 nmol/L in girls and 28.5 ± 17.0 nmol/L in boys during spring (P < 0.001) and 36.5 ± 20.3 nmol/L in girls and 45.0 ± 18.5 nmol/L in boys during autumn (P < 0.001). The prevalence of vitamin D deficiency was 93% during spring and 71% during autumn. There was a negative correlation between 25(OH)D and PTH levels (P < 0.01). We determined a cutoff point of serum 25(OH)D in which the mean serum PTH concentration began to increase as 35.8 nmol/L (P < 0.0001). The age, sex, and calcium level were found to be independent predictors for vitamin D deficiency.


CONCLUSIONS
Vitamin D deficiency is prevalent among healthy schoolchildren. It is noteworthy that 25(OH)D levels were significantly lower in girls and during autumn. We recommend vitamin D supplementation for children in addition to more time spent for outdoor activities for sensible sunlight exposure.
*Department of Pediatric Endocrinology †Department of Pediatrics, School of Medicine ‡Department of Public Health §Department of Biochemistry, Karadeniz Technical University, Trabzon, Turkey ||Vitamin D, Skin and Bone Research Laboratory, Section of Endocrinology, Nutrition and Diabetes, Department of Medicine, Boston University Medical Center, Boston, MA.
Gülay
G
Karagüzel
Beril
B
Dilber
Gamze
G
Çan
Ayşenur
A
Ökten
Orhan
O
Değer
Michael F
MF
Holick
D000293:Adolescent; D002648:Child; D003430:Cross-Sectional Studies; D019587:Dietary Supplements; D015444:Exercise; D005260:Female; D006801:Humans; D008297:Male; D010281:Parathyroid Hormone / Q000097:blood*; D012621:Seasons; D012737:Sex Factors; D013472:Sunlight; D011795:Surveys and Questionnaires; D014807:Vitamin D / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000097:blood; D014808:Vitamin D Deficiency / Q000097:blood / Q000453:epidemiology* / Q000517:prevention & control
D010281:Parathyroid Hormone; D014807:Vitamin D; C104450:25-hydroxyvitamin D