Calcium and vitamin d requirements of enterally fed preterm infants.
Pediatrics. 2013 May; 131(5):e1676-83
This review article refers to the calcium and vitamin D requirements of enterally fed preterm infants, a special population with unique bone mineral requirements, which differ substantially from those of full-term infants. These are the first guidelines regarding the dietary reference intakes of these nutrients in preterm infants published in the US, whereas corresponding recommendations have recently been published in Europe. It is a remarkable piece of work that has addressed the issue from many quarters, although there were few available or contradictory data.
Initially, the authors tried to clarify what the effects of preterm birth on mineral metabolism are. Although population-based studies are lacking, it is estimated that 10% to 20% of hospitalized infants with birth weight <1000g have radiographically defined rickets, despite current nutritional practices. Additionally, limited data indicate that only neonates with birth weight <1200g and those born small for gestational age or are exposed to corticosteroids (before or after birth) may have negative effects on bone health later in their life. As a result, the authors propose the screening of serum phosphatase activity (APA) and serum phosphorus at 4 to 6 weeks after birth in very low birth weight (VLBW) infants with birth weight <1500g (but not in those with birth weight >1500g) followed by biweekly monitoring, while the ultimate diagnosis of rickets requires a radiographic confirmation.
Moving on to the treatment of such cases, the authors clarify that unfortified human milk, parenteral nutrition, and infant formulas designed for full-term infants, including amino acid-based and soy-based formulas, do not contain enough calcium and phosphorus to fully meet the needs for bone mineralization in preterm infants. Of note, they state that phosphorus deficiency is at least as important, if not more important, than calcium deficiency in the etiology of bone mineralization deficits in this population.
Interestingly, the authors also reflect on several issues regarding the role and the requirements of vitamin D. At first controversy causes the fact that in utero, the skeletal mineralization is primarily independent of maternal vitamin D status. Moreover, in preterm infants, the calcium absorption fraction is reported to be relatively constant across a wide range of vitamin D intakes, while an unproven hypothesis suggests that in preterm infants most calcium absorption may occur independently of vitamin D in the first month after birth via a passive, paracellular mechanism. In addition, it is stated that data on the relationship between vitamin D intake and serum 25-OH-D in preterm infants are extremely limited, while data from full-term infants cannot easily be extrapolated to preterm infants, in whom UV B-mediated vitamin D formation is likely to be minimal during hospitalization and in whom fat mass, in which vitamin D and its metabolites are stored, is minimal.
Next, the authors give instructions on the basic approach for the prevention of rickets in preterm infants, through the use of formulas designed for preterm infants or human milk supplemented with fortifiers designed for use in this population. The recommendation is to use these products on the basis of birth weight (<1800 to 2000g) rather than gestational age, although further research is needed. Specific recommendations are given for calcium, phosphorus and vitamin D intakes. Additionally, other special management issues are discussed.
Significantly, the authors compare their recommendations with the European corresponding guidelines, which differ in suggesting a considerably lower target for calcium and phosphorus intake and higher intakes of vitamin D. Especially the issue of providing higher doses of vitamin D is dealt with circumspection since there are no safety data from providing 800-1000IU/day of vitamin D in preterm infants, which on a bodyweight basis may be 5 to 10 times the amount recommended for full-term neonates. The authors stress that even in preterm infants with radiologic evidence of rickets or high APA (>800IU/L)...
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