This trial objective is to assess whether doubling the daily intake of vitamin D improves serum vitamin D levels and serves as primary prevention of respiratory infections and asthma in premature infants.

This is a prospective randomized (1:1) double-blinded trial.

The study population will be randomized into two groups (1:1):

• Intervention Group - 800 IU of Vitamin D once daily
• Control Group - 400 IU of Vitamin D once daily Patients will be followed up for one year after randomization for serum Vitamin D levels and respiratory morbidity.

The rational of this trial is that a daily supplementation of a double dose of Vitamin D (800 IU instead of 400 IU) to late premature infants during the first year of life will result in elevated Vitamin D serum levels and in an improvement in respiratory morbidity.

This randomized trial of vitamin D supplementation is planned to determine the optimal dose of daily vitamin D supplementation required to achieve sufficient vitamin D levels in preterm infants and to assess whether doubling the daily intake of vitamin D may serve as primary prevention of respiratory infections and asthma in premature infants.

Inclusion Criteria:

1. Preterm infant born at 32+6 to 36+6 weeks of gestational age
2. Born at Soroka University Medical Center
3. Signed informed consent
4. Participants in the trial will be insured by "Clalit" HMO

Exclusion Criteria:

1. Chromosomal abnormality
2. Neurological or muscular congenital anomalies
3. Congenital cardiac defect
4. Congenital respiratory anomalies
5. Congenital GIT/ liver/ renal anomalies that effect the absorption and/or metabolism of Vitamin D and/or other substances.
6. Admission after birth to NICU persists more than 5 days