2.5. Follow-Up and Measurements
At baseline and after three months, parents were scheduled on a weekday to arrive at 6 a.m. in the morning at their daycare center for blood sampling. Because children were between 12 and 30 months of age, there was no fasting overnight. Venous blood samples (5 mL) were drawn from the antecubital vein at baseline and at the end of the study. Samples were obtained by a trained doctor according to protocol procedures established by the Biosafety Committee at the National Institute of Public Health (INSP). Serum and plasma samples were separated within 4 h of collection and stored at −70 °C until defrosted for analysis at the INSP nutrition laboratory. Total serum 25(OH)D concentration and parathyroid hormone (PTH) were measured using a chemiluminescent microparticle assay -CMIA- with an ArchitectHemoglobin concentration was taken for screening procedures, at baseline and then at three months after the start of supplementation, and determined in capillary blood samples obtained by finger prick and measured in Portable Photometer (HemoCue Hb 201+ (Hemocue.Hb201, Angelholm, Sweden) [