Bone mineralisation in premature infants cannot be predicted from serum alkaline phosphatase or serum phosphate

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.

Quantitative ultrasound assessment of bone health in the neonate

For a number of reasons there is a need to explore reliable non-invasive methods for assessing bone health in neonates and young infants. Epidemiological studies suggest that early events in life may predispose the adult to degenerative diseases such as osteoporosis. Preterm infants have an increased risk of low bone mass because of limited bone mass accretion in utero and a greater need for bone nutrients. Despite improvements in neonatal care fractures still occur. The diagnosis of osteopaenia of prematurity remains difficult as there is no screening test which is both sensitive and specific. Biochemical indices are non-diagnostic, and plain X-rays in the absence of fractures are poor at diagnosing bone disease. Although dual energy X-ray absorptiometry is increasingly used to assess bone mineral status in newborn infants, the size and immobility of the scanner, the length of time to perform the scan and use of ionising radiation make it unsuitable for routine use in the setting of the fragile very low birth weight infant. Quantitative ultrasound (QUS) was first developed in 1984, as a non-ionising, portable and low cost method of assessing bone health. The measurements obtained from QUS are thought to be related not only to the mineral density of the bone but also to reflect parameters of bone quality and strength. Preliminary studies suggest that this technique may be a useful method of assessing changes in bone health in preterm infants, but the data need to be interpreted carefully. This review will concentrate on the methodology of QUS and the studies that have already been performed in neonates.

Calcium nutrition and metabolism during infancy

Calcium is a vital mineral for the developing newborn infant. This review discusses perinatal and neonatal calcium metabolism, with an emphasis on enteral calcium absorption and the nutritional factors affecting calcium bioavailability including the three major endocrine hormones involved in calcium metabolism: parathyroid hormone, vitamin D, and calcitonin. The placenta transports calcium to the fetus throughout pregnancy, with the largest amount of fetal calcium accumulation occurring in the third trimester. At birth, the newborn transitions to intestinal absorption to meet the body's calcium needs. Most calcium is absorbed by paracellular passive diffusion in the small intestine. Calcium intestinal absorption is affected by the type and amount of calcium ingested. It is also affected by the amount of intestinal calcium that is bound to dietary fats and proteins. One major consequence of decreased calcium absorption is metabolic bone disease in which there is a failure of complete mineralization of the bone osteoid.

Assessment of skeletal development in preterm and term infants by quantitative ultrasound

Assessment of skeletal development using a nonionizing method would be desirable in critically ill preterm infants. We investigated the second metacarpus by quantitative ultrasound (QUS). Cross-sectional data were collected in 132 preterm or term infants measured within 24 h from birth and in 142 term infants up to the age of 18 mo. Longitudinal data were collected in 150 preterm infants up to the age of 14 mo. Cross-sectional data were used to devise reference curves for metacarpal speed of sound (mcSOS) and metacarpal bone transmission time (mcBTT). Both parameters increase during the last trimester of gestation. After birth, mcSOS declines up to the 6 mo and then increases up to 18 mo of life. McBTT values remain stable after birth. At birth, QUS values of preterm infants are lower than those observed at birth in term infants. In the longitudinal study, mcSOS showed a trend similar to that observed among term infants, nevertheless, values are lower up to 4-6 mo of life. Among preterm infants, mcBTT increases until it reaches values observed in term infants. Preterm infants in their first months of life have lower QUS values compared with term infants of same weight or length. This study demonstrates that it is possible to follow skeletal development and maturation by QUS in preterm infants. More specifically, the mcBTT values may provide information on bone tissue that is independent of length and weight of the preterm infant. The method here described is safe, repeatable, and reliable.

Nutrition of very low birth weight infants fed human milk with or without supplemental trace elements: a randomized controlled trial

BACKGROUND

Very low birth weight infants (<1500 g) have high nutritional needs. Deficiencies of minerals, trace elements (especially zinc) may develop as a result of rapid growth, low body stores and low content of these substances in human milk We hypothesized that fortification of human milk might prevent deficiencies.

METHODS

Prospective, randomized trial to evaluate mineral, trace element, thyroid status and growth of infants fed human milk fortified with different amounts of calcium, phosphorus and protein, with (BMF) or without (FM 85) trace elements. Sixty-two infants, 1000 to 1499 g birth weight, were randomized. Minerals and trace elements in serum, red blood cells and human milk and alkaline phosphatase activity, TSH, T4 and FT4 in serum were measured once until the fifth day and at 3 and 6 weeks of life. Clinical course and anthropometric measurements were recorded.

RESULTS

Intake of zinc, copper, manganese, calcium, phosphorus and magnesium was higher in the BMF group (P < 0.001). Serum zinc concentrations <0.49 mg/L occurred in 12% of the FM 85 group and 7% of the BMF group at 6 weeks (not significant). Median alkaline phosphatase activity was 436/379 IU/L in the FM 85/BMF group at 6 weeks (P < 0.01). The FM 85 group showed a higher weight gain (P < 0.05), possibly because of higher caloric (P < 0.01) and protein intake (P < 0.05) at 3 weeks.

CONCLUSIONS

Zinc deficiency was rare. Elevated intake of calcium, phosphorus and zinc was associated with lower serum alkaline phosphatase activity but did not influence serum zinc concentration.

Multicomponent fortified human milk for promoting growth in preterm infants

BACKGROUND

For term infants, human milk provides adequate nutrition to facilitate growth, as well as potential beneficial effects on immunity and the maternal-infant emotional state. However, the role of human milk in premature infants is less well defined as it contains insufficient quantities of some nutrients to meet the estimated needs of the infant. Observational studies have suggested that infants fed formula have a higher rate of growth than infants who are breast fed. However, there are potential short term and long term benefits from human milk. Commercially-produced multicomponent fortifiers provide additional nutrients to supplement human milk (in the form of protein, calcium, phosphate, and carbohydrate, as well as vitamins and trace minerals).

OBJECTIVES

The main objective was to determine if addition of multicomponent nutritional supplements to human milk leads to improved growth, bone metabolism and neurodevelopmental outcomes without significant adverse effects in premature infants.

SEARCH STRATEGY

Searches were made of the Cochrane Central Register of Controlled Trials (CENTRAL, The Cochrane Library, Issue 2, 3003), MEDLINE (searched August 29, 2003), previous reviews including cross references, abstracts, conferences and symposia proceedings, expert informants, journal handsearching mainly in the English language.

SELECTION CRITERIA

All trials utilising random or quasi-random allocation to supplementation of human milk with multiple nutrients or no supplementation in premature infants within a nursery setting were eligible.

DATA COLLECTION AND ANALYSIS

Data were extracted using the standard methods of the Cochrane Collaboration and its Neonatal Review Group, with separate evaluation of trial quality and data extraction by each author and synthesis of data using relative risk and weighted mean difference.

MAIN RESULTS

Supplementation of human milk with multicomponent fortifiers is associated with short term increases in weight gain, linear and head growth. There is no effect on serum alkaline phosphatase levels; it is not clear if there is an effect on bone mineral content. Nitrogen retention and blood urea levels appear to be increased. There are insufficient data to evaluate long term neurodevelopmental and growth outcomes, although there appears to be no effect on growth beyond one year of life. Use of multicomponent fortifiers does not appear to be associated with adverse effects, although the total number of infants studied and the large amount of missing data reduces confidence in this conclusion. Blood urea levels are increased and blood pH levels minimally decreased, but the clinical significance of this is uncertain.

REVIEWER'S CONCLUSIONS

Multicomponent fortification of human milk is associated with short-term improvements in weight gain, linear and head growth. Despite the absence of evidence of long-term benefit and insufficient evidence to be reassured that there are no deleterious effects, it is unlikely that further studies evaluating fortification of human milk versus no supplementation will be performed. Further research should be directed toward comparisons between different proprietary preparations and evaluating both short-term and long-term outcomes in search of the "optimal" composition of fortifiers.

Rickets

Rickets, once thought vanquished, is reappearing. In some less developed countries it hardly went away. This seminar reviews the effects of genes, stage of development, and environment on clinical expression of the disease. Rickets can be secondary to disorders of the gut, pancreas, liver, kidney, or metabolism; however, it is mostly due to nutrient deficiency and we concentrate on this form. Although calcium deficiency contributes in communities where little cows' milk is consumed, deficiency of vitamin D is the main cause. There are three major problems: the promotion of exclusive breastfeeding for long periods without vitamin D supplementation, particularly for babies whose mothers are vitamin D deficient; reduced opportunities for production of the vitamin in the skin because of female modesty and fear of skin cancer; and the high prevalence of rickets in immigrant groups in more temperate regions. A safety net of extra dietary vitamin D should be re-emphasised, not only for children but also for pregnant women. The reason why many immigrant children in temperate zones have vitamin D deficiency is unclear. We speculate that in addition to differences in genetic factors, sun exposure, and skin pigmentation, iron deficiency may affect vitamin D handling in the skin or gut or its intermediary metabolism.

Fracture and fortified breast milk in an extremely preterm infant

Metabolic bone disease (MBD) in the newborn predominantly affects preterm infants. The risk of MBD is inversely proportional to gestational age and birthweight, and directly related to postnatal complications. Poor bone mineralization has been shown in 55% of infants born at less than 1000 g. Optimal nutrition for very preterm infants is thought to be mother's own milk but supplementation is required to meet dietary requirements. However, there is insufficient evidence to determine that supplementation of human milk with commercial fortifiers has an effect on bone mineral content. We report a case of severe MBD with fractures in an extremely preterm infant who was fed with fortified mother's milk.