Reassessing vitamin D supplementation in preterm infants: a prospective study and review of the literature

Objectives: Recommendations for vitamin D (VitD) intake and target serum levels of 25(OH)D in preterm infants are diverse. We hypothesized that preterm infants with low birth weight (BW) have low dietary intake of VitD and therefore should be supplemented with higher amounts of VitD. Methods: Infants with BW < 2 kg were supplemented with 600 units of VitD a day during the first 2-6 weeks of life, whereas infants with BW>2 kg continued with the routine supplementation of 400 units of VitD daily. Serum levels of 25(OH)D, calcium, phosphorous, alkaline phosphatase (AP) and parathyroid hormone (PTH) were assessed 24 h after birth and before discharge. The total daily intake of vitD was calculated in each infant. Results: Sixty-two infants were enrolled, 49 with BW < 2 kg. After birth, only 24% had sufficient levels of 25(OH)D, whereas before discharge 45 of 54 infants (83%) available for analysis reached sufficient levels of 25(OH)D. All 54 infants demonstrated significant elevation in serum levels of calcium, phosphorous, AP and significant reduction in PTH levels. The total daily intake of VitD was lower than recommended (800-1000 IU/d) in 16 of 45 infants with BW < 2 kg (36%) and in all nine infants with BW>2 kg. Nevertheless, only 2 of 25 infants with insufficient intake of VitD demonstrated insufficient levels of serum 25(OH)D. No case of vitamin D excess was recorded. Conclusions: Increased supplementation of VitD (600 IU/d) for premature newborns with BW < 2 kg is effective in increasing both total daily intake of VitD and serum levels of 25(OH)D.