Vitamin D status and predictors of hypovitaminosis D in Italian children and adolescents: a cross-sectional study

Hypovitaminosis D affects children and adolescents all around the world. Italian data on vitamin D status and risk factors for hypovitaminosis D during pediatric age are lacking. Six hundred fifty-two children and adolescents (range 2.0–21.0 years) living in the northwestern area of Tuscany were recruited at the Department of Pediatrics, University Hospital Pisa. None of them had received vitamin D supplementation in the previous 12 months. 25-hydroxyvitamin D (25-OH-D) and parathyroid hormone (PTH) levels were analyzed in all subjects. Severe vitamin D deficiency was defined as serum levels of 25-OH-D < 25.0 nmol/L (10.0 ng/mL) and vitamin D deficiency as < 50.0 nmol/L (20.0 ng/mL). Serum 25-OH-D levels of 50.0–74.9 nmol/L (20.0–29.9 ng/mL) indicated vitamin D insufficiency, whereas 25-OH-D levels ≥ 75.0 nmol/L (30.0 ng/mL) were considered sufficient. Hypovitaminosis D was defined as 25-OH-D levels < 75.0 nmol/L (30.0 ng/mL). The median serum 25-OH-D level was 51.8 nmol/L, range 6.7–174.7 (20.7 ng/mL, range 2.7–70.0), with a prevalence of vitamin D deficiency, insufficiency, and sufficiency of 45.9, 33.6, and 20.5 %, respectively. The prevalence of severe vitamin D deficiency was 9.5 %. Adolescents had lower median 25-OH-D levels (49.8 nmol/L, range 8.1–174.7; 20.0 ng/mL, range 3.2–70.0) than children (55.6 nmol/L, range 6.8–154.6; 22.3 ng/mL, range 2.7–61.9, p = 0.006). Non-white individuals (n = 37) had median serum 25-OH-D levels in the range of deficiency (28.2 nmol/L, range 8.1–86.2; 11.3 ng/mL, range 3.2–34.5), with 36/37 having hypovitaminosis D. Logistic regression showed significant increased risk of hypovitaminosis D in the following: blood samples taken in winter (odds ratio (OR) 27.20), spring (OR 26.44), and fall (OR 8.27) compared to summer; overweight (OR 5.02) and obese (OR 5.36) subjects compared to individuals with normal BMI; low sun exposure (OR 8.64) compared to good exposure, and regular use of sunscreens (OR 7.06) compared to non-regular use. Gender and place of residence were not associated with vitamin D status. The 25-OH-D levels were inversely related to the PTH levels (r = −0.395, p < 0.0001). Sixty-three out of the 652 (9.7 %) subjects showed secondary hyperparathyroidism. Conclusion Italian children and adolescents who were not receiving vitamin D supplementation had high prevalence of hypovitaminosis D. Careful identification of factors affecting vitamin D status is advisable to promptly start vitamin D supplementation in children and adolescents.