Vitamin D and Health Outcomes in Preterm Born Population

To investigate the effect of one year vitamin D supplementation in preterm born adults (4000 IU = 100 micrograms a day if serum concentration is \< 30 nmol/l, 2000 IU = 50 micrograms a day if 30-50 nmol/l and 1000 IU = 25 micrograms a day if \> 50-80 nmol/l, and no additional supplement if \> 80 nmol/l) on health outcomes (bones, teeth, muscles, heart, lungs) . The target level of vitamin D concentration by every 4 months interval is 80 - 120 nmol/l .(Preterm Adult group)