**2.3 Blood testing**

*Vitamin D Deficiency*

of these findings [7, 9, 14–20].

**2. Materials and methods**

or > 10,000 inhabitants, respectively).

**2.2 Clinical examination**

**2.1 Participants**

needed to evaluate the underlying mechanisms.

associated factors among children in northern Spain.

as well as a risk to present autoimmune, endocrine, infectious, psychiatric, and/or neurological diseases and several types of cancer [1, 4, 7–13]. Additional studies are

In other words, in addition to its contribution to bone metabolism, vitamin D seems to fulfill a broad spectrum of biological functions related to cell proliferation, differentiation, and metabolism, which justifies the interest in monitoring its body content. Gender, age, race, season of the year in which serum is collected, sun exposure, and nutritional status have been associated with lower levels of serum calcidiol, but there are disparities among the different authors in the interpretation

The aim of this study is to determine the prevalence of hypovitaminosis D and

The present work is a cross-sectional study conducted in a sample of 602 individuals from ages 3.1 to 15.4 years after the completion of a clinical examination and blood testing in the period January 2014 to December 2014. Tests were carried out in the Pediatric Endocrinology Unit of our hospital. Tanner's criteria were evaluated in every individual and were used in the assignment of individuals in two different groups: school group (Tanner stage I) and adolescent group (Tanner stages II–V). The characteristics of the place of residence were recorded as urban or rural (<

All individuals were healthy Caucasian children living in Navarra, Spain. They were selected from the external consultations of the different pediatric subspecialties and were not affected by any chronic pathology with potential interference in growth, body composition, food ingestion, or physical activity. Any participant under treatment with concrete medications (antiepileptic drugs or glucocorticoids),

Body measurements (weight and height) were taken in specific conditions (underwear, barefoot). An Año-Sayol scale (reading interval 0–120 kg and a precision of 100 g) was used for weight registration and a Holtain wall stadiometer (reading interval 60–210 cm, precision 0.1 cm) for height registration. The program Aplicación Nutricional, from the Spanish Society of Pediatric Gastroenterology, Hepatology and Nutrition (Sociedad Española de Gastroenterología, Hepatología y Nutrición Pediátrica, available at http://www.gastroinf.es/nutritional/), provided the estimates of the Z-score values of BMI. The reference charts used for comparison were the graphics from Ferrández et al. (Centro Andrea Prader, Zaragoza 2002). The values of Z-score enabled the assignment of individuals in the following groups:

• Normal: Z-score between −1.0 (15th percentile) and + 1.0 (85th percentile)

• Overweight: Z-score > 1.0 (85th percentile)

• Severe obesity: Z-score > 3.0 (99th percentile)

• Obesity: Z-score > 2.0 (97th percentile)

vitamin D, or calcium supplements was put aside from our sample.

**16**

The plasma levels of calcium and phosphorous were determined in a fasting sample of blood using colorimetric methods in a cobas 8000 analyzer (Roche Diagnostic, Mannheim, Germany). The determination of calcidiol levels required a high-specific chemiluminescence immunoassay (LIAISON Assay, Diasorin, Dietzenbach, Germany) and the determination of PTH levels a highly specific solid-phase, two-site chemiluminescent enzyme-labeled immunometric assay in an Immulite analyzer (DPC Biermann, Bad Nauheim, Germany).

The distribution of individuals according to Vitamin D plasma levels followed the criteria of the US Endocrine Society [21, 22]. Calcidiol plasma levels lower than 20 ng/ml (<50 nmol/L) corresponded to Vitamin D deficiency, calcidiol levels between 20 and 29 ng/ml (50–75 nmol/L) to Vitamin D insufficiency, and concentrations equal to or higher than 30 ng/ml (>75 nmol/L) to Vitamin D sufficiency. PTH serum levels higher than 65 pg/ml [14, 17] determined secondary hyperparathyroidism.
