Hypercalciuria in premature infants receiving high mineral-containing diets

Bone disease of prematurity

Bone disease of prematurity is a complication of preterm birth. This article reviews the aetiology, treatment and prevention of bone disease of prematurity. Provision of adequate nutrition including energy, protein, and minerals is required for both treatment and prevention. Screening for bone disease is controversial. While further research is required quantitative ultrasound appears to be a promising tool for screening and monitoring response to therapy. Further research is needed before recommending physical activity to prevent bone disease of prematurity.

Calcium and phosphorus nutrition in preterm infants

Metabolic bone disease is a common event in preterm infants. Between 24 wk gestation and term, the fetus accrues approximately 80% of body Ca, P and Mg. Consequently, preterm infants miss in part or completely the period of greatest mineral accretion. Ca and P requirements in preterm infants are based on demands for matching intrauterine bone mineral accretion rates and on maintenance of normal serum Ca and P concentrations. Daily physical therapy may be a useful adjunct, as it is associated with a significant increase in bone mineral density and content. Osteopenia/rickets of prematurity seems to be a self-resolving disease. However, this does not imply that a period of demineralization is acceptable. While the potential long-term consequences on peak bone mass are unclear at the moment, the short-term benefits include the avoidance of fractures, less marked dolicocephaly and improved linear growth.

Nutrient requirements for preterm infant formulas

Achieving appropriate growth and nutrient accretion of preterm and low birth weight (LBW) infants is often difficult during hospitalization because of metabolic and gastrointestinal immaturity and other complicating medical conditions. Advances in the care of preterm-LBW infants, including improved nutrition, have reduced mortality rates for these infants from 9.6 to 6.2% from 1983 to 1997. The Food and Drug Administration (FDA) has responsibility for ensuring the safety and nutritional quality of infant formulas based on current scientific knowledge. Consequently, under FDA contract, an ad hoc Expert Panel was convened by the Life Sciences Research Office of the American Society for Nutritional Sciences to make recommendations for the nutrient content of formulas for preterm-LBW infants based on current scientific knowledge and expert opinion. Recommendations were developed from different criteria than that used for recommendations for term infant formula. To ensure nutrient adequacy, the Panel considered intrauterine accretion rate, organ development, factorial estimates of requirements, nutrient interactions and supplemental feeding studies. Consideration was also given to long-term developmental outcome. Some recommendations were based on current use in domestic preterm formula. Included were recommendations for nutrients not required in formula for term infants such as lactose and arginine. Recommendations, examples, and sample calculations were based on a 1000 g preterm infant consuming 120 kcal/kg and 150 mL/d of an 810 kcal/L formula. A summary of recommendations for energy and 45 nutrient components of enteral formulas for preterm-LBW infants are presented. Recommendations for five nutrient:nutrient ratios are also presented. In addition, critical areas for future research on the nutritional requirements specific for preterm-LBW infants are identified.

Metabolic bone disease of prematurity

Metabolic bone disease is recognized with increasing frequency in very-low-birth-weight infants. Radiological changes characteristic of rickets have been found in 55% of infants with a birth weight of less than 1000 g and in 23% of infants weighing less than 1500 g at birth. Twenty-four per cent of infants with a birth weight of less than 1500 g have fractures. The main aetiological factor is insufficient phosphorus supplementation. The aetiology is, however, multifactorial and also includes calcium deficiency, vitamin D deficiency, certain drugs, aluminium loading and immobilisation. The method of choice in detecting subclinical mineral bone disease of prematurity is measurement of bone mineral density, but there is as yet no single good diagnostic method available for premature infants. The optimal mineral and vitamin D requirement of the premature infant must be established so that proper recommendations can be given. The current recommended vitamin D dose in Europe (ESPGAN 800-1000 IU/day) is probably too high when extra minerals are supplied. Moreover, the duration of mineral supplementation may need to be continued until the infant has reached a body weight of 3.5 kg. This article deals with the aetiology, pathogenesis, diagnosis and future prospects of metabolic bone disease of prematurity.

Zinc and calcium apparent absorption from an infant cereal: a stable isotope study in healthy infants

Fractional apparent absorption of Zn and Ca from a wheat-milk-based infant cereal was studied in six healthy infants (18-30 weeks old). Mineral absorption was measured by a stable-isotope technique based on faecal excretion of the isotopes. Each test meal (40 g cereal) was extrinsically labelled with 70Zn and 42Ca before intake. All faecal material passed during the 21 d following intake of the labelled test meal was collected on trace-element-free nappies. Individual stool samples were analysed for their content of ‘OZn and 42Ca by thermal ionization mass spectrometry. Apparent absorption was calculated as intake minus total faecal excretion of the isotopes over 68-92 h after administration. The fractional apparent absorption values for Zn and Ca were 33.9 (SD 164) % (range 19.2-639 %) and 53.5 (SD 12.6) %) (range 36.7-71.7 %) respectively. Re-excretion of absorbed 70Zn (> 68-92 h to 21 d after intake of the labelled meal) was 044 (SD 038) %] of administered dose while only one infant re-excreted detectable amounts of 42Ca (1.74%) of administered dose). The analysis of individual stool samples confirmed that 72 h is a sufficient time period for complete collections of non-absorbed isotopes in faecal material from infants during the weaning period and that re-excretion of initially absorbed 70Zn and 42Ca (> 68-92 h to 21 d after intake of the labelled meal) is negligible.