Vitamin D requirement in infants receiving parenteral nutrition

Calcium and Phosphorous in Pediatric Parenteral Nutrition

Calcium (Ca) and phosphorus (P) are essential for various systemic functions, including bone mineralization. Adequate provision of Ca and P in pediatric parenteral nutrition (PN) solutions is necessary for skeletal growth and for the prevention of metabolic bone disease. The provision of adequate doses of Ca and P in pediatric PN solutions is complicated by the increased needs in preterm and term infants, solubility limitations, and venous access. Clinicians should be aware of the evidence that supports the optimal use of Ca and P in pediatric PN solutions, including studies that have evaluated dosing and solubility. The aim of this article is to review relevant literature and practices for the use of these two minerals in pediatric PN solutions. The vitamin D endocrine system, a critical component for Ca homeostasis and bone mineralization, is discussed, as well as clinical manifestations of metabolic bone disease and methods for its prevention, assessment, and treatment in pediatric patients receiving PN.

Early postnatal calcium and phosphorus metabolism in preterm infants

OBJECTIVES

Bone mineralisation in preterm infants is related to the supply of calcium (Ca) and phosphorus (P). We increased the amount of minerals in parenteral nutrition (PN) for preterm infants and evaluated postnatal Ca and P metabolism in relation to mineral and vitamin D (vitD) intake.

METHODS

Preterm infants, included on their first day of life, received standard PN, providing a maximum Ca/P intake of 3/1.92 mmol · kg(-1) · day(-1) on day 3. Ca/P content of formula was 2.5/1.6 mmol/dL, and fortified human milk was 2.4/1.95 mmol/dL. PN supplied 80 IU · kg(-1) · day(-1) vitD. Formula and fortified human milk contained 200 IU/dL of vitD. During a 5-week period, serum concentrations and urinary excretion of Ca/P were registered and related to the intake of minerals and vitD.

RESULTS

During 12 months, 79 infants (mean gestational age 29.8 ± 2.2 weeks, mean birth weight 1248 ± 371 g) were included. The recommended intake for minerals was achieved by day 5 and for vitD by 4 weeks. Infants developed hypercalcaemia, hypercalciuria, and hypophosphataemia during the first postnatal week, leading to the additional P supplementation in 49 infants. The renal tubular reabsorption of P was >95% until day 9 but decreased <70% after the second week. Alkaline phosphatase was normal at birth, increased to a maximum of 450 IU/L by day 14, and remained above the normal range for the remaining period.

CONCLUSIONS

Parenteral intake of P appeared to be too low, leading to mineral imbalances in the early postnatal period, and vitD intake was also below recommendations.

Vitamin D deficiency in patients receiving home parenteral nutrition

BACKGROUND

In addition to its role in bone metabolism, vitamin D has important immunomodulatory and antineoplastic effects. Patients on home parenteral nutrition (HPN) receive most of their vitamin D from intravenous (IV) supplementation. Vitamin D deficiency is common in the general population, and the adequacy of vitamin D supplementation in HPN patients is unclear. The purpose of this study is to determine the vitamin D status of patients on HPN.

METHODS

Consecutive patients seen in a regional home nutrition program had their oral and IV vitamin D intakes determined. Plasma 25-hydroxyvitamin D levels were measured in all patients. Intake of calcium, magnesium, and phosphate were also determined.

RESULTS

The mean 25-hydroxyvitamin D level in 22 patients receiving HPN for a mean of 33.5 months (range, 1-177) was 42 nmol/L. Vitamin D deficiency was present in 15 (68%) patients and vitamin D insufficiency in 6 (27%) patients. The mean dietary vitamin D intake was 79.5 IU per day, while the mean IV supplementation was 166 IU per day.

CONCLUSIONS

In this study of a regional Canadian HPN program, there was a high prevalence of vitamin D deficiency/insufficiency affecting virtually all patients. All patients receiving HPN should be supplemented with vitamin D and have their 25-hydroxyvitamin D levels monitored. Further studies are required to determine optimal methods and dosing of vitamin D replacement using oral supplements or ultraviolet light therapy.

Harry M. Vars Research Award. Increase in lumbar spine bone mineral content in patients on long-term parenteral nutrition without vitamin D supplementation

BACKGROUND

We had previously shown that short-term withdrawal of vitamin D in patients with metabolic bone disease complicating home parenteral nutrition (HPN) corrected osteomalacia. We therefore conducted a prospective study of the effect of long term withdrawal of vitamin D in patients on home parenteral nutrition.

METHODS

Baseline measurements of bone mineral content, serum levels of calcium, phosphorus, parathormone, 25-OH and 1,25 (OH)2D; urinary calcium; and bone mineral density were measured. Then all parenteral vitamin D was withdrawn and the above parameters were followed for a mean of 4.5 years.

RESULTS

Lumbar spine bone mineral content (LSBMC) was 0.79 +/- 0.06 g/cm2 at the start of the study, well below the reference value, 1.16 +/- 0.13 g/cm2. Parathyroid hormone (PTH) (0.48 +/- 0.24 pmol/L) and 1,25-(OH)2D levels (22.8 +/- 7.9 pmol/L) were low and 25-hydroxyvitaniin D levels were normal (33.3 +/- 5.5 nmol/L) before removing vitandn D from the HPN solutions. After withdrawal of vitamin D for 4.5 +/- 0.2 years LSBMC increased from 0.79 +/- 0.06 to 0.93 0.07 g/cm2 (p < 0.005). Calcium phosphorus, magnesium and 25-hydroxyvitamin D did not change significantly, 1,25(OH)2D, and PTH levels became normal after withdrawal of vitamin D.

CONCLUSIONS

In selected patients with depressed PTH levels, long-term withdrawal of vitamin D during HPN increases LSBMC and levels of PTH and 1,25(OH)2D. There is no reduction of the mean level of 25-hydroxyvitamin D.

Effect of parenteral calcium and phosphorus therapy on mineral retention and bone mineral content in very low birth weight infants

HYPOTHESIS

If calcium and phosphorus are administered to very low birth weight infants in amounts larger than those currently used in standard parenteral nutrition solutions, apparent retention of calcium and phosphorus (intake minus urinary excretion) will increase and bone mineralization will improve.

DESIGN

Randomized, controlled, double-blind trial.

SETTING

Neonatal intensive care unit.

PATIENTS

Twenty-four very low birth weight infants (< 1.2 kg) expected to receive parenteral nutrition exclusively for approximately 3 weeks beginning 3 days after birth.

INTERVENTIONS

Infants received parenteral nutrition solutions, either the standard mixture containing 1.25 mmol calcium and 1.5 mmol phosphorus per deciliter (group STAND: n = 12, birth weight 921 +/- 171 gm, gestational age 27 +/- 2 weeks (mean +/- SD)) or 1.7 mmol calcium and 2.0 mmol phosphorus per deciliter (group HIGH: n = 12, 857 +/- 180 gm, 27 +/- 2 weeks).

MAIN OUTCOME MEASURES

Intake, urinary excretion, and apparent retention of calcium, phosphorus, and magnesium every 3 days during parenteral nutrition therapy. Serum indexes of mineral status twice during therapy. Bone mineral content of the distal segment of the left radius at 1, 4, 8, and 26 weeks.

RESULTS

Apparent calcium retention (1.2 +/- 0.2 vs 1.6 +/- 0.2 mmol.kg-1.d-1) and phosphorus retention (1.4 +/- 0.2 vs 1.8 +/- 0.4 mmol.kg-1.d-1) differed significantly (p < 0.01) between groups STAND and HIGH, respectively; neither changed with the duration of parenteral nutrition therapy. Serum calcium, magnesium, parathyroid hormone, 25-hydroxyvitamin D, and osteocalcin concentrations were similar in both groups. Serum phosphorus concentration was significantly higher in group HIGH than in group STAND (p = 0.025). The absolute bone mineral content and the rate of increase in bone mineral content between 1 and 4, 1 and 8, and 1 and 26 weeks were significantly greater in group HIGH than in group STAND.

CONCLUSIONS

Increased parenteral intakes of calcium and phosphorus resulted in greater retention of these minerals during parenteral nutrition therapy and in greater bone mineral content after therapy.

Parenteral nutrition-related bone disease

Parenteral nutrition (PN)-related bone disease remains a problem in patients of all ages. Understanding of the pathogenesis of PN-related bone disease is complicated by the effect of underlying illnesses, therapeutic interventions, and pre-existing nutrition deficiencies before the initiation of PN therapy. Interrelation of various nutrients, for example, calcium, phosphorus, and vitamin D, in their effects on bone mineralization, demands simultaneous assessment of the role of multiple nutrients and increases the difficulty in defining the role of a single nutrient in the development of bone disease. However, recent reports indicate that there exist a number of factors important in the development of PN-related bone disease and some factors such as increased mineral requirement are unique to growing infants whereas other factors such as aluminum toxicity may be common to both adult and pediatric populations. Nonnutritional factors, including chronic use of potent loop diuretics and altered acid-base status, can affect urine mineral loss, cell metabolism, and bone mineralization, particularly in small, preterm infants. Current evidence indicates that the cause of PN-related bone disease is multifactorial, and the prevention of PN-related bone disease awaits better delineation of the exact sequence of pathogenic events.

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.

Response of preterm infants to aluminum in parenteral nutrition

Twenty-five preterm infants with birth weights (BW) 540 to 2280 g (20 with birth weight less than 1500 g) and gestational ages 24 to 37 weeks, were studied to determine the response to 2 levels of aluminum (Al) loading from currently unavoidable contamination of various components of parenteral nutrition (PN) solution. High Al loading group (H) received solutions with measured Al content of 306 +/- 16 micrograms/liter and low A1 loading group (L) received solutions with 144 +/- 16 micrograms A1/liter. Urine Al:Creatinine (Al:Cr) ratios (micrograms:mg) became elevated and significantly higher in H (1.6 +/- 0.38 vs 0.5 +/- 0.1, p less than 0.05) at the third sampling point (mean 19 days). Serum Al concentrations were highest at onset in both groups and stabilized with study but remained consistently higher than the normal median of 18 micrograms/liter. Calculated urine Al excretion were consistently low and were 34 +/- 6% vs 28 +/- 5% in the H and L groups, respectively. One infant in the L group who died 39 days after termination of above study showed the presence of A1 in bone trabeculae and the presence of excessive unmineralized osteoid along the trabeculae. We conclude that small preterm infants are able to increase urine Al excretion with increased Al load. However urine Al excretion is incomplete with bone deposition of Al and persistently elevated serum Al concentrations.

Vitamin concentrations in very low birth weight infants given vitamins intravenously in a lipid emulsion: measurement of vitamins A, D, and E and riboflavin

Because total parenteral nutrition with vitamins added to the glucose-amino acid mixture is often associated with a reduction in blood levels of vitamin A (retinol) during the routine treatment of many very low birth weight (VLBW) infants (less than 1500 gm), and because retinol losses in the plastic delivery system can be prevented by adding the vitamins to an intravenous lipid emulsion, seven VLBW infants with a mean birth weight of 900 gm (range 450 to 1360 gm) were given 40% of a unit dose vial, per kilogram of body weight, of a multivitamin preparation (M.V.I. Pediatric) (280 micrograms retinol; 160 IU vitamin D; 2.8 mg tocopherol; 0.68 mg riboflavin) in a lipid emulsion, Intralipid. After treatment with the intralipid-vitamin mixture for 19 to 28 days, plasma vitamin A (retinol) concentrations increased significantly from 11.0 +/- 0.76 (mean +/- SEM) before intralipid to 19.2 +/- 0.97 micrograms/dl after the intralipid-vitamin mixture (p less than 0.01); 25-hydroxyvitamin D concentrations increased from an initial value of 12.6 +/- 2.6 to 20.2 +/- 1.9 mg/dl (p less than 0.01); alpha-tocopherol concentrations increased from an initial value of 0.31 +/- 0.06 to 2.44 +/- 0.13 mg/dl (p less than 0.01); and riboflavin levels increased from 64.1 +/- 7.8 ng/ml to concentrations between 20 and 100 times the initial level. Erythrocyte riboflavin levels increased from 71.8 +/- 14 initially to 166 +/- 41 ng/gm hemoglobin, and erythrocyte flavin-adenine dinucleotide levels increased similarly from 972 +/- 112 initially to 2005 +/- 294 ng/gm hemoglobin. These results show that the addition of M.V.I. Pediatric to Intralipid decreases the extensive in vivo loss of retinol and is associated with an increase in plasma retinol concentrations in VLBW infants. The daily doses of vitamins D (160 IU/kg) and E (2.8 mg/kg) appear sufficient, but the dose of vitamin A (280 micrograms/kg) is insufficient to raise blood levels of all infants into the normal range. The current dose of riboflavin is excessive and may be harmful.