It has not yet been established the optimal dose of vit. D for preterm infants in Poland. It is not known what dose of vit. D will provide the correct concentration of vit. D and the optimal development of the skeleton of the premature.

The study will try to determine the optimal supplementation of vitamin D and the supply of Ca and P for normal growth and development of a child born prematurely.

In addition, the investigators will evaluate any risk factors for deficiency and excess of vitamin D and the consequences of its deficiency and overdose. Simultaneously the study would make possible the determination of an optimal schedule for controlling the Ca-P levels in the group of the youngest infants born prematurely. In addition, the study will assess the relationship between maternal and newborn vitamin D resources right after birth, and the incidence of vitamin D deficiency in infants born prematurely. Preterm infants will be randomized in 3 groups assigned to different doses of vit. D. The study will investigate the metabolism of calcium, phosphorus, the health of bones and development of the premature babies till the age of 2.

The participants of the study will be prematures, born ≤32 GA, hospitalized in the Department of Neonatology, in the neonatal intensive care unit. Hospitalized patients who meet the inclusion criteria will be randomized in 3 groups assigned to different doses of vit. D (400, 800 or 1200 units(UNT) of vitamin D).

At defined age points of postnatal life, parameters of calcium and phosphorus metabolism and vitamin D level will be tested, along with the health of bones, health status and development.

Inclusion Criteria:

• gestational age ≤32 weeks at birth
• hospitalization in the department no later than at the age of 7 days (for infants born outside the center)
• No birth defects or diseases permanently affecting the ability to accept enteral feeding
• Anticipated possibility of continuous monitoring of the course of treatment in hospital until discharge
• Consent of Parents / legal guardians for the participation in the study.

Exclusion criteria

• gestational age> 32 weeks at birth
• the beginning of hospitalization in the department later than the age of 7 days (for infants born outside the center)
• presence of congenital defects or diseases permanently affecting the ability to accept enteral feeding (e.g.oesophageal atresia, anal atresia, congenital umbilical hernia, gastroschisis, syndromes genetically determined)
• significant interruption (> 1 week) of the hospitalization in the center
• lack of consent of the Parents / legal guardians to participation in the study