Phosphorus deficiency syndrome in very low birth weight infants

Increasing gap in human height between rich and poor countries associated to their different intakes of N and P

We analyzed mean height of men born in the 1960s, 1970s and 1980s in 80 countries. Both height and the change in height during the last decades were correlated with N and P intake, as well as the N:P intake ratio. Rich countries had higher per capita N and P intake than poor countries (on average 19.5 ± 0.3 versus 9.66 ± 0.18 kg N y-1 and 2.17 ± 0.04 versus 1.35 ± 0.02 kg P y-1), and also larger increases in per capita N intake (12.1 ± 2.0% vs. 7.0 ± 2.1%) and P intake (7.6 ± 1.0% vs 6.01 ± 0.7%), during the period 1961-2009. The increasing gap in height trends between rich and poor countries is associated with an increasing gap in nutrition, so a more varied diet with higher N, P, and N:P intake is a key factor to improve food intake quality in poor countries and thus shorten the gap with rich countries. More N and P are needed with the consequent requirements for a better management of the socioeconomic and environmental associated problems.

Changes in red cell phosphate metabolism of preterm and fullterm infants with perinatal problems during their first month of life

The effects of perinatal problems on red cell phosphate metabolism were studied in two groups of infants (preterms B and fullterms D) during the first month of life. All infants started milk feeding from day three after birth. The results were compared to those of healthy preterms (A) and fullterms (C), respectively. Comparisons were also made between the preterm and fullterm groups B and D. The preterms with perinatal problems (B) showed a significant delay in catching up with the plasma and red cell inorganic phosphate (Pi) levels of controls (A) throughout the first month of life (p < 0.05). In parallel, the erythrocyte 2,3 diphosphoglycerate (2,3-DPG) concentrations of the sick preterms lagged significantly behind those of controls (p < 0.001); but the ATP levels were comparable between the two groups. The fullterms behaved slightly differently. No significant differences in plasma Pi (Pl Pi) and red cell 2,3-DPG were seen between the sick and healthy neonates during the month of study, while red cell Pi (RBC Pi) and ATP were found to be lower in the sick ones (p < 0.05). The fullterms with perinatal problems (D) had significantly higher Pl Pi (p < 0.05) and RBC Pi (p < 0.01) than preterms with problems (B) from the first week of life and continued in a similar pattern until the end of the month. Red cell 2,3-DPG concentrations were found to be significantly correlated with Pl Pi and RBC Pi in both preterm groups (p < 0.01) and in the sick fullterms (p < 0.001) during the time of the study. In the healthy fullterms 2,3-DPG was found to correlate only with red cell Pi (p < 0.05). Perinatal problems seem to affect Pi metabolism to a different degree in preterm and fullterm neonates in the first month of life.

High-turnover osteopenia in preterm infants: determination of urinary pyridinium cross-links of collagen

Osteopenia is a frequent condition in preterm infants, but its pathogenesis is uncertain. In the present study, we measured longitudinal changes in the excretion of pyridinium cross-links of collagen (specific markers of bone resorption) and evaluated the relationship between collagen cross-links and other indexes of bone and renal function in preterm infants. In these infants, urinary collagen cross-links were markedly increased on day 7 and day 30 of life and at estimated full-term gestation. The values were several times higher than those of older children and almost comparable to those of healthy full-term infants. Cross-link excretion did not correlate with beta2-microglobulin (B2M) or N-acetyl-beta-D-glucosaminidase (NAG) activity (markers of renal function), indicating that cross-link excretion is not influenced directly by infantile renal function. High serum osteocalcin and low bone mineral density (BMD) in the lumbar spine were also observed at estimated full-term gestation. There was no significant correlation between collagen cross-link excretion and either serum osteocalcin or spine BMD. We conclude that a state of high bone turnover underlies the development of osteopenia in preterm infants.

Urinary excretion of pyridinium cross-links of collagen in infancy

This cross-sectional study evaluated urinary excretion of pyridinium cross-links of collagen, specific markers of ongoing bone resorption, in infants aged 1 week to 7 months and examined the relationship between urinary cross-links and individual renal function. Spot urines from a total of 100 infants were analyzed. The collagen cross-links, pyridinoline (Pyd) and deoxypyridinoline (D-Pyd), were assayed by fluorescence detection after high-performance liquid chromatography (HPLC). Beta2-Microglobulin (beta2M), an index of renal tubular function, was determined by radioimmunoassay. In healthy term infants, urinary collagen cross-links were several times higher than the reported data for older children, with peak values seen at 1 month of age. Excretion of Pyd and D-Pyd was also markedly elevated in 1-month-old preterm infants, despite poor somatic growth. Such high excretion of collagen cross-links probably reflects the state of accelerated bone turnover in infancy. The postnatal change in the cross-links was different from that in urinary beta2M, and the values obtained did not correlate with beta2M in either term or preterm infants. These results indicate that cross-link excretion is not influenced directly by individual renal function.

Phosphate metabolism in the red cell of sick prematures

The effect of different amounts of phosphorus supplementation on phosphate metabolism was studied in two groups of sick preterms (B and C) during the first week of life. Group B included prematures that started formula milk feeding from day 3 and group C neonates on total parenteral nutrition with phosphate supplementation for 7 days. Twelve healthy preterm neonates on formula milk feeding from day 2 (group A) were used as controls. On the 7th day of life all phosphate parameters measured in group C (plasma and red cell inorganic phosphate and erythrocyte ATP and 2,3-diphosphoglycerate) were found significantly lower than in the controls (1.60 +/- 0.07; 0.60 +/- 0.08; 1.45 +/- 0.09 and 4.42 +/- 0.18 vs. 2.05 +/- 0.10; 0.94 +/- 0.11; 1.69 +/- 0.07 and 6.24 +/- 0.42 mmol/l, respectively). The renal tubular reabsorption of phosphate was also lower in this group (86.8 +/- 3.2 vs. 97.3 +/- 1.0%). No significant differences were observed between groups B and A. Higher phosphorus intake that was better achieved through early milk feeding prevented phosphate depletion and the decline of 2,3-diphosphoglycerate in the erythrocytes even of sick neonates which in turn might help to improve tissue oxygenation. The amount of parenteral phosphate supplementation that could have beneficial effects on red cell phosphate parameters needs further investigation.

Mineral requirements of low-birth-weight infants

The minerals calcium (Ca), magnesium (Mg), and phosphorus (P) are essential for tissue structure and function. Recent studies have resulted in a more rational approach to the management of mineral intake in preterm infants receiving parenteral nutrition (PN) and enteral nutrition (EN). For preterm infants requiring PN, the use of PN solutions with a Ca content of 1.25-1.5 mmol/dl (50-60 mg/dl), a P content of 1.29-1.45 mmol/dl (40-45 mg/dl), and an Mg content of 0.2-0.3 mmol/dl (5-7 mg/dl) is supported by studies of mineral homeostasis with serial chemical and calciotropic hormone measurements, standard balance studies, and improved radiographic indices of bone mineralization. For infants requiring EN, an intake of approximately 4 mmol (200 mg) of Ca, 3.2 mmol (100 mg) of P, and 0.33 mmol (8 mg) of Mg/kg/day based on an average retention rate of 64% for Ca, 71% for P, and 50% for Mg should be sufficient to meet the requirements of preterm infants in early infancy. This level of intake is supported by data from balance studies using standard and stable isotope techniques, changes in bone mineral content (BMC) measurements, and calciotropic hormone data. Based on the timing of development of fractures and rickets, changes in BMC, and skeletal growth data, the increased Ca and P intake should continue for at least 3 months after birth or until reaching a body weight of about 3.5 kg. In addition, nonnutritional factors may have the potential to increase mineral loss and disturb mineral homeostasis; chronic diuretic therapy increases mineral loss, and aluminum contamination of nutrients theoretically may compound any skeletal disorder. Thus, attention to the level of mineral intake and factors important in mineral loss and mineral metabolism should optimize mineral retention in small preterm infants.

Evaluation of lumbar bone mineral density by dual energy x-ray absorptiometry

Using dual-energy x-ray absorptiometry (DEXA), the lumbar spinal bone mineral density (BMD) in 49 Japanese children with or without metabolic bone disease (MBD) was determined. The following results were obtained: (a) The normal data for healthy Caucasians (J Clin Endocrinol Metab 1990; 70: 1330-1333) appear to be applicable to Japanese children; (b) BMD was normal in patients with congenital hydronephrosis with normal renal function; (c) One patient with congenital renal failure and one with Lowe syndrome had low BMD, but the MBD in the former improved markedly with peritoneal dialysis; (d) A reduced BMD was found in patients treated with long-term steroids, probably because of decreased turnover of bone; (e) A reduction in BMD was pronounced in preterm infants during the first few months of life. In conclusion, DEXA is a useful method of bone densitometry in MBD in children.

Disorders of calcium and phosphorus homeostasis

Calcium and phosphorus are, respectively, the fifth and sixth most abundant elements in the body; both play vital roles in a multitude of physiologic systems. Because the great bulk of these elements is found in the skeleton, a large part of the discussion of calcium and phosphorus metabolism focuses on skeletal disorders, the impact of which falls heavily on young children. This article reviews the physiology of calcium and phosphorus, the skeletal and systemic consequences of disorders of vitamin D nutrition and metabolism, and the metabolic bone disease of prematurity.

Plasma ionized calcium, phosphate and magnesium in preterm and small for gestational age infants

Blood concentrations of ionized calcium, phosphate and magnesium were determined on days 1, 3 and 5 in 32 preterm infants, appropriate for gestational age, and 25 small for gestational age infants. The results were compared with those of a reference group of 31 fullterm newborns. Preterm infants had lower mean ionized calcium levels than the reference population. Ionized calcium levels were positively correlated with gestational age and postnatal age. The sickest infants had the lowest calcium levels. Intrauterine growth retardation did not seem to influence the calcium levels. Small for gestational age infants had lower phosphate values than the reference group and the values correlated with the degree of growth retardation the first day. Magnesium concentrations increased with time and did not differ significantly between the study groups and the reference group. Magnesium values did not correlate with calcium or phosphate values.

Improved bone mineral status in very low birthweight infants fed human milk mixed with preterm formula

The bone mineral status of very low birthweight (VLBW) infants fed exclusively their own mother's milk (group I) was compared with that of VLBW infants fed mother's milk in the initial 4 weeks followed by a 1:1 mixture of mother's milk and preterm formula containing high phosphorus (P) and calcium (Ca) (group II). In both groups, most infants showed a biochemical picture characteristic of phosphorus deficiency syndrome by the fourth week. Thereafter, serum alkaline phosphatase activity (ALP) decreased and serum P increased in all group II infants. Conversely, serum ALP rose and hypophosphatemia persisted in most group I infants. Group II had a significantly higher serum P at weeks 8 and 12 and a significantly lower ALP at week 12 than group I. Furthermore, group II had a lower incidence of severe radiographic abnormalities than group I at week 12. We confirmed previous observations that VLBW infants fed exclusively human milk require P and Ca supplementation to prevent metabolic bone disease of prematurity.