Vitamin D nutritional status in preterm infants and response to supplementation

Little is known about vitamin D status in preterm infants and their response to supplementation. To investigate this, we assessed serum 25-hydroxyvitamin D (25OHD) levels using RIA in a consecutive sample of stable preterm very low birth weight (VLBW) infants (born <= 32 weeks gestation or birth weight <= 1.5 kg), and we explored associated factors. Serum 25OHD level was first assessed once infants were tolerating feeds (n 274). If this first 25OHD level was below 50 nmol/l (20 ng/ml), which is the level associated with covering requirements in terms of skeletal health in the majority, then we recommended prolonged augmented vitamin D intake (>= 10 mu g (400 IU) daily) from a combination of fortified feeds and vitamin supplements and follow-up re-assessment at approximately 6 weeks corrected age (n 148). The first assessment, conducted at a median for chronological age of 18 (interquartile range (IQR) 11-28) d, found that 78% had serum 25OHD levels below 50 nmol/l. Multivariable analysis demonstrated that the determinants of serum 25OHD levels were duration of vitamin D supplementation and gestational age at birth (r(2) 0.215; P<0.001). At follow-up, after a median of 104 (IQR 78-127) d, 87% achieved levels >= 50 nmol/l and 8% had levels > 125 nmol/l, a level associated with potential risk of harm. We conclude that low 25OHD levels are an issue for preterm VLBW infants, warranting early nutritional intervention. In infants with serum 25OHD levels <50 nmol/l, a vitamin D intake of >= 10 mu g (400 IU) daily achieves target levels in the majority; however, further work is needed to determine the exact dose to safely meet target levels without overcorrection.