Etiologic factors in rickets of very low-birth-weight infants

Metabolic Bone Disease in Premature Neonates: An Unmet Challenge

Metabolic bone disease (MBD) is an important cause of morbidity in premature, very low birth weight (VLBW) and sick infants and, if left undiagnosed, may lead to structural deformities and spontaneous fractures. MBD is defined as impaired bone mineralization in a neonate with lower than expected bone mineral levels in either a fetus or a neonate of comparable gestational age and/or weight, coupled with biochemical abnormalities with or without accompanying radiological manifestations. MBD has been reported to occur in 16% to 40% of extremely low birth weight neonates and presents by 6-16 weeks after birth. Insufficient calcium and phosphorous stores during the phase of accelerated growth predispose to MBD in neonates along with the use of some medications such as caffeine or steroids, prolonged parenteral nutrition and chronic immobilization. Enhanced physical activity in preterm infants facilitates bone mineralization and weight gain. Biochemical abnormalities tend to worsen significantly, as the severity of disease progresses. These abnormalities may include hypocalcemia, hypophosphatemia, hyperphosphatasia and secondary hyperparathyroidism. In addition, urinary phosphate wasting and hypovitaminosis D can be additional complications. Conversely, biochemical abnormalities may not be accompanied by rachitic changes. Newer diagnostic modalities include non-invasive bone densitometry by quantitative ultrasound over the mid-tibial shaft. The management of MBD includes adequate calcium, phosphorous and vitamin D supplementation, along with optimum nutrition and physical activity. Similarly, preventive strategies for MBD should target nutritional enhancement in combination with enhanced physical activity. MBD usually results in preventable morbidity in preterm and VLBW neonates. Treatment consists of optimum nutritional supplementation and enhanced physical activity.

Use of Soy-Based Formulas and Cow's Milk Allergy: Lights and Shadows

Soybean (Glycine max) is a species of legume native to East Asia and used in childhood diet for over 2,000 years in the East. Soy protein formulas have been available for almost a century. Nowadays, the increase in cow's milk allergy and vegetarian dietary preferences are driving consumers toward cow's milk alternatives. In this paper, we reviewed the nutritional composition of soy-based infant formula and discussed their possible use in pediatric age, mainly focusing on prevention and treatment of cow's milk allergy. Protein quality is determined by digestibility and amino acid content. Purified or concentrated vegetable proteins (e.g., soy protein and gluten) have high digestibility (>95%), similar to those of animal ones. For some intact vegetable products (e.g., whole cereals and pulses), protein digestibility is lower (80-90%). Food processing and heat treatment also influence protein digestibility. Considering these data, we tried to evaluate the possible use of soybean and derivatives in pediatric age, including the nutritional composition of soy formulas and the clinical indications for their use. Moreover, since plant-based beverages are being perceived as healthy by consumers and their use is growing on the market, we recommend that soy drink should not be used as a substitute for infant formulas or cow's milk in children younger than 24 months.

Assisted Physical Exercise for Improving Bone Strength in Preterm Infants Less than 35 Weeks Gestation: A Randomized Controlled Trial

Objective

To compare the efficacy of daily assisted physical exercise (starting from one week of postnatal age) on bone strength at 40 weeks of post menstrual age to no intervention in infants born between 27 and 34 weeks of gestation.

Design

Open-label randomized controlled trial.

Setting

Tertiary-care teaching hospital in northern India from 16 May, 2013 to 21 November, 2013.

Participants

50 preterm neonates randomized to Exercise group (n=26) or Control group (n=24).

Intervention

Neonates in Exercise group underwent one session of physical exercise daily from one week of age, which included range-of-motion exercises with gentle compression, flexion and extension of all the extremities with movements at each joint done five times, for a total of 10-15 min. Infants in Control group underwent routine care and were not subjected to any massage or exercise.

Outcome measures

Primary: Bone speed of sound of left tibia measured by quantitative ultrasound at 40 weeks post menstrual age. Secondary: Anthropometry (weight length and head circumference) and biochemical parameters (calcium, phosphorus, alkaline phosphatase) at 40 weeks post menstrual age.

Results

The tibial bone speed of sound was comparable between the two groups [2858 (142) m/s vs. 2791 (122) m/s; mean difference 67.6 m/s; 95% CI -11 to 146 m/s; P=0.38]. There was no difference in anthropometry or biochemical parameters.

Conclusion

Daily assisted physical exercise does not affect the bone strength, anthropometry or biochemical parameters in preterm (27 to 34 weeks) infants.

Metabolic bone disease in the preterm infant: Current state and future directions

Neonatal osteopenia is an important area of interest for neonatologists due to continuing increased survival of preterm infants. It can occur in high-risk infants such as preterm infants, infants on long-term diuretics or corticosteroids, and those with neuromuscular disorders. Complications such as rickets, pathological fractures, impaired respiratory function and poor growth in childhood can develop and may be the first clinical evidence of the condition. It is important for neonatologists managing such high-risk patients to regularly monitor biochemical markers for evidence of abnormal bone turnover and inadequate mineral intake in order to detect the early phases of impaired bone mineralization. Dual-energy X-ray absorptiometry has become an increasingly used research tool for assessing bone mineral density in children and neonates, but more studies are still needed before it can be used as a useful clinical tool. Prevention and early detection of osteopenia are key to the successful management of this condition and oral phosphate supplements should be started as soon as is feasible.

Safety of soya-based infant formulas in children

Soya-based infant formulas (SIF) containing soya flour were introduced almost 100 years ago. Modern soya formulas are used in allergy/intolerance to cows' milk-based formulas (CMF), post-infectious diarrhoea, lactose intolerance and galactosaemia, as a vegan human milk (HM) substitute, etc. The safety of SIF is still debated. In the present study, we reviewed the safety of SIF in relation to anthropometric growth, bone health (bone mineral content), immunity, cognition, and reproductive and endocrine functions. The present review includes cross-sectional, case-control, cohort studies or clinical trials that were carried out in children fed SIF compared with those fed other types of infant formulas and that measured safety. The databases that were searched included PubMed (1909 to July 2013), Embase (1988 to May 2013), LILACS (1990 to May 2011), ARTEMISA (13th edition, December 2012), Cochrane controlled trials register, Bandolier and DARE using the Cochrane methodology. Wherever possible, a meta-analysis was carried out. We found that the anthropometric patterns of children fed SIF were similar to those of children fed CMF or HM. Despite the high levels of phytates and aluminium in SIF, Hb, serum protein, Zn and Ca concentrations and bone mineral content were found to be similar to those of children fed CMF or HM. We also found the levels of genistein and daidzein to be higher in children fed SIF; however, we did not find strong evidence of a negative effect on reproductive and endocrine functions. Immune measurements and neurocognitive parameters were similar in all the feeding groups. In conclusion, modern SIF are evidence-based safety options to feed children requiring them. The patterns of growth, bone health and metabolic, reproductive, endocrine, immune and neurological functions are similar to those observed in children fed CMF or HM.

Standard two-compartment formulation for total parenteral nutrition in the neonatal intensive care unit: A fluid tolerance based system

The nutrient requirements of most (pre) term newborns receiving intensive care appear to be relatively fixed. The range of optimal fluid load however, is perceived as being quite narrow and highly variable in time. We designed four amino acid-dextrose mixtures for a standardized neonatal parenteral nutrition, delivering a fixed amount of nutrients in four dilutions with water and corresponding to a fluid load of 90, 110, 130 or 170 ml/kg per day. The addition of a lipid emulsion completes the TPN. In a pilot study, we followed the weight of 30 very low birthweight infants on this parenteral nutrition. After a stabilisation period, the weight gain was found to be similar to the normal fetal weight accretion in utero. We have now infused these solutions in to more than 1000 infants, without significant complications. These formulations proved to have substantial advantages compared to the individualized prescription in terms of availability, safety and time- and cost-effectiveness.

Calcium and phosphorus retention in the preterm infant during total parenteral nutrition. A comparative randomised study between organic and inorganic phosphate as a source of phosphorus

The preterm infant fed parenterally is prone to some demineralisation due in part to insufficient Calcium (Ca) and Phosphorus (P) retention. In an attempt to augment Ca and P retention, we prepared a standardised parenteral solution containing calcium gluconate and glucose-1-phosphate (Phocytan) as source of phosphorus, yielding a daily supply of 75 mg/kg Ca and 45 mg/kg P. 28 very low birthweight infants were randomly assigned to receive either this solution (high Ca P ; n = 15) or a conventional formulation containing calcium gluconate and potassium mono- and dibasic phosphate delivering 42 mg/kg Ca and 36 mg/kg P daily (low Ca P ; n = 13). In the high Ca P daily retention was respectively 80% and 99% for Ca and P whereas in the low Ca P group, retention was 70% and 82%. Serum parathormone levels were significantly lower in the high Ca P group. We conclude that parenteral nutrition with a new high Ca P supplement results in an augmented Ca and P retention in very low birthweight infants. This may help to prevent neonatal bone demineralization.

Association between calcium in cord blood and newborn size in Bangladesh

Ca status in the uterus during pregnancy has been suggested to affect fetal growth and size at birth. In Bangladesh, low Ca levels in pregnant women and low birth weight in infants are common. The present study explored the association between Ca levels in cord blood and newborn size at birth (birth weight and birth length) in Bangladesh. Samples and data included 223 women with live-born singleton deliveries in rural Bangladesh. Newborn weight and length were measured at birth. From cord blood obtained at delivery, Ca, 25-hydroxy vitamin D, bone-specific alkaline phosphatase and intact parathyroid hormone levels were determined. An association between size at birth and Ca levels in cord blood was found (birth weight, P = 0.022; birth length, P = 0.001). Associations between Ca and newborn size were further analysed using multivariate regression analyses. After adjusting for several covariates of characteristics in mothers and newborns (gestational weeks at birth, sex of newborn, socio-economic status, maternal height, BMI, age and season at birth), birth length still exhibited a significant relationship with Ca levels in cord blood (birth length, P = 0.030). The present study indicates that Ca status in cord blood might be associated with the birth length of newborns. Ca levels during gestation may affect fetal growth.

Growth and bone mineralization in children born prematurely

OBJECTIVE

To study the growth and bone mineralization of children born prematurely.

STUDY DESIGN

A cohort of healthy children who were born prematurely with birth weight less than 1.5 kg were compared by weight and height to a national reference. Bone mineral status of preterm infants was compared with children who were born at term gestation. The average follow-up was 7 years. A sample of children who were born prematurely was recalled from an infant nutrition study. Children born at term gestation who had similar body weight for age were recruited from the community. Bone mineral evaluation was conducted in a group of 20 children born prematurely with birth weight less than 1.5 kg and in 15 children born at term gestation. Body weight for age was similar between the groups. All children were born of appropriate size for gestational age at birth. All children had their body weight and height measured. Comparisons for growth assessment status were made with the NHANES III database and published standards. Dietary intakes and food frequency were analyzed. The bone mineral status was measured at two sites, lumbar spine and distal third radius bone.

RESULTS

The average age was 7 years, with a range of 5 to 9 years. Compared with the reference population, children who were born prematurely on the average had lower weights, heights and body mass index. Preterm children had a lower lumbar bone mineral content than term children, 12.8+/-3.0 and 14.7+/-2.2 g cm(-1) (P<0.05). The lumbar bone mineral density was lower in the preterm group than in the term group, 0.525+/-0.062 and 0.574+/-0.073 g cm(-2), respectively (P<0.04). Three of the preterm children had a history of fracture whereas none of the term children reported any fractures.

CONCLUSION

Children who were born prematurely with birth weights less than 1.5 kg tend to be significantly smaller for age and have lower lumbar spinal bone mineral content and density compared with children born at term gestation.

Use of soy protein-based formulas in infant feeding

Soy protein-based formulas have been available for almost 100 years. Since the first use of soy formula as a milk substitute for an infant unable to tolerate a cow milk protein-based formula, the formulation has changed to the current soy protein isolate. Despite very limited indications for its use, soy protein-based formulas in the United States may account for nearly 25% of the formula market. This report reviews the limited indications and contraindications of soy formulas. It will also review the potential harmful effects of soy protein-based formulas and the phytoestrogens contained in these formulas.

Quantitative ultrasound in the evaluation of bone status in premature and full-term infants

Metabolic bone disease of prematurity (MBDP) is a common and significant problem that often gives rise to osteopenia, fractures, osteomalacia, and osteoporosis. The purpose of our study is to establish normative data on bone status in premature and full-term infants to help future studies on MBDP. Bone status was prospectively determined as part of a multicenter study among newborns within 96 hours of life. The patients were divided into 2 groups: group 1 included those neonates 25-36 wk gestational age (premature), and group 2 neonates were born at 37-42 wk gestational age (full term). Demographic data were collected. The Omnisense 7000 Bone Sonometer (Sunlight Medical Ltd., Tel-Aviv, Israel) was used to determine the speed of sound (SOS) through the mid tibia, which reflects bone strength. A total of 235 patients were enrolled in this study. Group 1 (i.e., the premature infants) had a statistically lower age-adjusted SOS as compared with group 2 (i.e., the full-term infants) (analysis of variance; p=0.001). There was also a correlation between SOS and birth weight (r=0.3; p<001). This study represents the largest database of normative data for bone status measuring in preterm and term infants.

The role of cord blood IGF-I levels in preterm osteopenia

OBJECTIVE

Osteopenia is a frequent condition in preterm infants. This prospective study was designed to assess the relationship between cord blood insulin-like growth factor-I (IGF-I) levels and bone mineralization in healthy premature infants.

METHODS

Twenty preterm infants (ten males and ten females) were studied. We determined the bone mineral density (BMD) and bone mineral content (BMC) of healthy premature infants by dual-energy X-ray absorptiometry and also studied the correlation between IGF-I and other parameters and the influence of cord blood IGF-I concentrations on bone mineralization in these infants.

RESULTS

The mean concentration of IGF-I was 13.6 +/- 16.9 ng/ml and BMD and BMC were 0.249 +/- 0.06 g/cm2 and 3.09 +/- 1.18 g, respectively. Cord serum levels of IGF-I had significantly positive correlations with BMD (r = 0.605, p = 0.008), but not BMC (r = 0.242, p = 0.367). In stepwise regression analysis, IGF-I emerged as a significant predictor of BMD (beta = 0.595, p = 0.015) contributing to 35.4% of its variability.

CONCLUSION

We found a relationship between cord blood IGF-I and BMD in preterm neonates, suggesting that even within an unremarkable population, IGF-I might be important to ensuring bone health.

Renal phosphate handling of premature infants of 23-25 weeks gestational age

Premature infants with low serum phosphate concentrations (<2 mmol/l) are at risk for osteopenia. Therefore, serum phosphate levels in premature infants should be kept above 2 mmol/l. Premature infants of 26-31 weeks gestational age (GA) have renal phosphate threshold concentrations (Tp/GFR) in the range of normal serum phosphate values (2 mmol/l). Therefore, these infants show significant urinary phosphate excretion only when serum phosphate levels are normal, and urinary phosphate excretion can be used to monitor phosphate supplementation. However, few data are available on extremely premature infants of 23-25 weeks GA. The objective of this study was to compare Tp/GFR levels in infants of 23-25 weeks GA to those in infants of 26-31 weeks GA. We retrospectively evaluated case notes of 12 infants of 23-25 weeks GA and compared them to 19 infants of 26-31 weeks GA. Tp/GFR was calculated from simultaneous measurements of urinary phosphate, urinary creatinine, serum phosphate, and serum creatinine. Tp/GFR values 3-5 weeks postnatally were lower in infants of 23-25 weeks GA (1.06+/-0.36 mmol/l, p<0.001) than in infants of 26-31 weeks GA (1.76+/-0.26 mmol/l). Near term (35-37 weeks postmenstrual age), there was no significant difference between Tp/GFR values in infants of 23-25 weeks GA (1.83+/-0.32 mmol/l) and in infants of 26-31 weeks GA (2.05+/-0.22 mmol/l). We conclude that at 3-5 weeks postnatally, infants of 23-25 weeks GA are at risk for low Tp/GFR values, leading to urinary phosphate excretion even in the presence of low serum phosphate levels. In these infants, serum phosphate levels should be monitored, and phosphate supplementation should be adjusted to keep serum phosphate levels above 2 mmol/l.

Early physical activity intervention prevents decrease of bone strength in very low birth weight infants

OBJECTIVE

To evaluate the effect of early range-of-motion intervention on bone strength and bone turnover in very low birth weight infants.

METHODS

Twenty-four infants (mean birth weight: 1135 +/- 247 g; mean gestational age: 28.5 +/- 2.3 weeks) were matched for gestational age and birth weight and then randomly assigned into exercise (n = 12) and control (n = 12) groups. Exercise protocol started at the first week of life and involved daily extension and flexion range of motion against passive resistance of the upper and lower extremities (5 minutes per day, 5 days per week, 4 weeks). Growth parameters, bone strength, and biochemical markers of bone homeostasis were measured at enrollment and after 4 weeks. Bone strength was determined using quantitative ultrasound measurement of bone speed of sound (SOS) at the middle left tibial shaft.

RESULTS

Bone SOS decreased significantly in the control group during the study period (from 2892 +/- 30 m/sec to 2799 +/- 26), whereas bone SOS of the exercise group remained stable (2825 +/- 32 m/sec and 2827 +/- 26 m/sec at baseline and 4 weeks, respectively). This significant difference in bone SOS was not expressed in the biochemical markers of bone homeostasis.

CONCLUSIONS

There is a significant postnatal decrease in the bone SOS of very low birth weight infants. A brief range-of-motion exercise attenuates the decrease in bone strength and may decrease the risk of osteopenia.

The effect of neonatal sepsis on bone turnover in very-low birth weight premature infants

Neonatal sepsis is very common in preterm infants, and severe morbidity during the neonatal period is a major cause of osteopenia of prematurity. We examined the effect of neonatal sepsis on bone turnover markers in premature infants. Twenty-four premature infants participated in the study. Ten of the premature infants developed sepsis during their hospitalization in the neonatal intensive care unit (mean gestational age [GA] 27.3 +/- 0.4 weeks; mean birth weight [BW] 898 +/- 82 g). Fourteen infants who did not develop sepsis served as controls (GA: 26.8 +/- 0.8 weeks, BW: 892 +/- 66 g). Blood samples for bone turnover markers were collected during the initial sepsis workup, and at the end of the first week of treatment, and were compared to the corresponding weekly changes in bone markers in the controls. In addition, samples were collected at the end of the 10th week of life to determine long-term effects of sepsis on bone turnover. Bone osteoblastic activity was assessed by measurements of circulating osteocalcin, bone-specific alkaline phosphatase (BSAP) and the C-terminal procollagen peptide (PICP) levels. Bone resorption was assessed by measurements of circulating carboxy terminal cross-links telopeptide of type I collagen (ICTP). There were no significant differences in the weekly changes of all bone turnover markers in premature infants who developed or did not develop sepsis. No significant differences were found in bone turnover markers at the age of 10 weeks between the groups. Neonatal sepsis in premature infants was not associated with biochemical evidence of reduced bone turnover.

Increments in whole body bone mineral content associated with weight and length in pre-term and full-term infants during the first 6 months of life

BACKGROUND

The objective of the present study was to assess bone mineral content (BMC) of the whole skeleton in pre-term and full-term healthy infants and the factors influencing BMC, such as bone area, birth weight, birth length, current weight, current length, gender, and gestational age.

METHODS

Forty-eight healthy full-term infants and 34 healthy premature infants fed predominantly with intact human milk were studied. BMC was measured monthly with dual energy X-ray absorptiometry (DEXA). At the same time, length and weight were measured and registered. Pre-term infants were studied at 60-day intervals.

RESULTS

For both full-term and pre-term infants, BMC increased during the first months of life. However, the values of pre-term infants never reached the values of full-term infants, even after correcting for age and weight. For both full-term and pre-term infants, BMC was significantly correlated at the second month with birth weight (r = 0.901), birth length (r = 0.860), gestational age (r = 0.803), bone area (r = 0.960), current weight (r = 0.920), and current length (r = 0.840, p <0.001 for all correlation coefficients). Multivariate analysis revealed that bone area was the most important factor in predicting BMC.

CONCLUSIONS

Pre-term children have lower BMC than full-term children. The main factor explaining this apparent osteopenia is bone area. Pre-term children have a higher daily mineralization rate than full-term children, but this catch-up mineralization is not enough to reach BMC levels seen in full-term children.

Measurements of bone turnover markers in premature infants

We determined the levels of circulating bone turnover markers in preterm infants during the first weeks of life. Twenty premature infants (mean gestational age 27+/-2.2 weeks, mean birth weight 894+/-231 g) hospitalized in the neonatal intensive care unit (NICU) at the Meir General Hospital, Israel, participated in the study. Measurements of bone turnover markers were performed at birth, and every week thereafter for an average follow-up of 11.2+/-0.7 weeks. Bone osteoblastic activity was assessed by measurements of circulating osteocalcin, bone-specific alkaline phosphatase (BSAP) and the C-terminal procollagen peptide (PICP) levels. Bone resorption was assessed by measurements of serum levels of the carboxy-terminal cross-links telopeptide of type I collagen (ICTP). All three markers of osteoblastic activity increased markedly and significantly during the first three weeks of life, and then continued to increase gradually until week 10 (p<0.01). Circulating ICTP levels increased in the first week of life and then decreased gradually throughout the follow-up (p<0.01). The study participants were divided into premature infants born at extremely low birth weight (ELBW: <1000 g, n=12) and very low birth weight (VLBW: 1000-1250 g, n=8). Osteocalcin (in weeks 2-5 of life), PICP (weeks 3-5), and ICTP levels (weeks 2-3) were significantly higher in VLBW preterms. These results suggest increased bone formation in premature infants in the first three months of life. The increased bone turnover in VLBW compared to ELBW premature infants may be the result of a generally higher morbidity in ELBW preterm infants in early stages of life.

Bone mineral metabolism in the micropremie

Environmental factors, nutritional supplies, hormonal status, diseases, and treatments appear to affect postnatal skeletal growth and mineralization in VLBW infants. Compared with their term counterparts, ELBW infants are at risk of postnatal growth deficiency and osteopenia at the time of hospital discharge. From recent data, DXA is becoming one of the reference techniques to evaluate mineral status, whole-body composition, and effects of dietary manipulations on weight gain composition and mineral accretion in preterm infants. Weight gain and length increases need to be evaluated carefully during the first weeks of life, in the intensive care unit and out of it, in the step down unit. Nutritional survey is required to improve the nutritional supply and to maximize linear growth. As the critical epoch of growth extends, during the first weeks or months after discharge, follow-up and nutritional support need to be provided during the first years to promote early catch-up growth and mineralization. Further studies need to determine precisely the most optimal feeding regimen during this period but also need to evaluate the long-term implications of such a policy on stature, peak bone mass, and general health at adulthood.

A high prevalence of metabolic bone disease in exclusively breastfed very low birthweight infants in Dar-es-Salaam, Tanzania

Metabolic bone disease (MBD), or rickets, is common in very low birthweight infants. A descriptive, cross-sectional, hospital-based study was carried out at Muhimbili Medical Centre, Dar-es-Salaam from 15 April to 30 June, 1995 to discover the magnitude, contributory factors, morbidity and suitable biochemical diagnostic tests for MBD. One hundred infants with a postnatal age of 6-12 weeks, whose birthweights were 1500 g or less were studied. Thirty-three of 100 (33%) infants, 16 boys and 17 girls, were radiographically diagnosed as having metabolic bone disease. The mean (SD) gestational age of those infants was 30.4 (2.7) weeks, while that of the infants without metabolic bone disease was 32.4 (3) weeks (p = 0.003). There was no significant difference in birthweight, serum calcium and serum phosphate levels between those infants with MBD and those without. The mean (SD) serum alkaline phosphatase in infants with MBD was 1052.9 (493.3) U/l and 766.8 (301.7) in those without MBD (p = 0.006). Thus, metabolic bone disease is common in very low birthweight infants. Wrist radiography and serum alkaline phosphatase levels remain important diagnostic tools. MBD should be considered seriously in very low birthweight infants.

Laboratory assessment of nutritional metabolic bone disease in infants

OBJECTIVES

There are numerous laboratory investigations available for the assessment of an infant with suspected metabolic bone disease (MBD); thus, comprehensive laboratory investigations on every aspect of MBD would impose unnecessary stress to the infant and the costs involved would be prohibitive. An overview of the assessment of an infant with suspected MBD, in particular, nutrition-related bone disease, is presented. Our objectives include an understanding of: 1. the importance of appropriate information from history and physical examination to guide the laboratory investigations; 2. relevance and limitations of specific laboratory investigations: a. radiologic studies include diagnostic radiographs and quantitative bone mass determination by dual energy x-ray absorptiometry, b. biochemical measurements to determine mineral homeostasis and bone turnover, c. vitamin (vitamin D metabolites) and hormonal (parathyroid hormone and calcitonin) measurements; with respect to diagnosis and monitoring of the natural progress or response to therapy.

CONCLUSION

Relevant information from clinical history and physical examination, and an understanding of the role and limitations of various laboratory investigations, would allow the optimal utilization of laboratory tests in the assessment of an infant with MBD.

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.

Calcium, magnesium and phosphorus in the nutrition of the newborn

Several factors have been suggested to contribute to inadequate bone mineralization in infants. Calcium and phosphorus intakes in preterm infants are below the intrauterine accretion rates. Calcium retention is influenced by the types of calcium salts used and by alterations in dietary phosphorus, fat and carbohydrates. Dietary intakes of vitamin D, and modifications in the protein base of infant formula, e.g., soy base vs cow milk base, may impact bone mineralization. The major hormonal mechanisms involved in the regulation of bone mineralization are parathyroid hormone, calcitonin and vitamin D. From recent animal studies, it has been suggested that parathyroid hormone related peptide (PTH-rp) may also play a role in perinatal calcium homeostasis.

Minerals and trace elements in infant nutrition

Little information is available on absorption and metabolism of minerals and trace elements during infancy. The lack of data is related to the methodological problems involved in these studies. By using stable isotopes as labels, studies can be conducted in infants without introducing exposure to radiation, or any other risk, and studies on bioavailability of minerals and trace elements during early life can therefore be performed. This paper discusses results from studies of trace element/mineral absorption and metabolism in infants, based on stable isotope techniques.

High turnover osteopenia in preterm babies

Osteopenia is common in preterm babies, but its pathogenesis is uncertain. In this study bone density in babies was quantitated, postnatal bone mineralization compared to expected intrauterine bone mineralization and the pathogenesis of osteopenia investigated. Healthy babies (103 term, 76 preterm) were examined clinically, biochemically and radiologically the day after birth and at a time corresponding to expected full term gestation. Appendicular bone density was quantitated by magnification radiogrammetry, using the humeral cortical index (CI). The CI of preterm and term babies was similar the day after birth. In preterm babies elevated serum alkaline phosphatase and high urinary hydroxyproline indicated increased bone turnover. The CI of preterm babies at expected full term gestation was lower (p = 0.0001) than that of term babies at birth, implying that postnatal bone mineralization lagged behind expected intrauterine bone mineralization. Radiologic data suggested increased endosteal resorption rather than decreased bone formation. At expected full term gestation the preterm babies had higher serum alkaline phosphatase and urinary calcium, phosphate, c-AMP and hydroxyproline (p = 0.0001) than term babies at birth, and 15% had periosteal reactions. The biochemical as well as the radiologic data therefore indicated high turnover osteopenia in preterm babies. We conclude that postnatal bone mineralization in preterm babies lagged significantly behind expected intrauterine bone mineralization and that the osteopenia observed in preterm babies is caused by increased bone resorption and not by decreased bone formation. The cause(s) of this high turnover osteopenia, however, remains to be ascertained.

Role of plasma phosphate measurements in detecting rickets of prematurity and in monitoring treatment

Twice weekly plasma and urine measurements were made in 24 very low birth weight infants. Intravenous feeding was given whilst infants required respiratory support. Subsequently they received breast milk or formula milk with a vitamin D supplement of 400 U/day. Fourteen babies required intravenous feeding for more than 10 days. Six developed radiological rickets or severe osteoporosis, and these infants had plasma phosphate levels < 1.2 mmol/L on breast milk or < 1.8 mmol/L on formula milk. Babies without radiological rickets had plasma phosphate levels > 1.2 mmol/L on breast milk and > 1.8 mmol/L in all but one on formula milk. Successful treatment of rickets was associated with a rise in plasma phosphate to the above levels. Untimed urine calcium and phosphate concentrations expressed as creatinine ratios were not helpful in detecting babies with rickets, but may be useful in monitoring therapy.

Bone mineralization in the first year of life in infants fed human milk, cow-milk formula, or soy-based formula

OBJECTIVE

To test the hypotheses that (1) bone mineral content (BMC) is similar in infants fed soy-based formula (SBF) and human milk (HM) and higher in infants fed cow milk-based formula (CBF) and (2) serum 1,25-dihydroxyvitamin D, an index of mineral sufficiency, is similar in infants fed formula and infants fed HM.

DESIGN

Randomized, prospective study of formula-fed group only.

SETTING

Recruitment was in a normal newborn nursery.

PATIENTS

72 infants: 10 given HM, 20 given CBF (Similac), 21 given SBF (Isomil), and 21 given SBF (Prosobee).

MEASUREMENTS

BMC and 1,25-dihydroxyvitamin D levels at baseline (days 2 through 7 of life) and at 8, 16, 26, and 52 weeks of age. The BMC was similar in all groups at all times; serum 1,25-dihydroxyvitamin D levels were similar in all groups, except that they were elevated at 8, 16, and 26 weeks in those fed Prosobee.

CONCLUSIONS

(1) BMC is similar in SBF-, CBF-, and HM-fed infants and (2) compensatory elevation of serum 1,25-dihydroxyvitamin D concentrations may occur in SBF-fed infants.

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.

Calcium and phosphorus metabolism in the premature infant

During the last trimester of pregnancy, there is a sixfold increase in fetal calcium and phosphorus accumulation. Unsupplemented human breast milk may not provide sufficient calcium and phosphorus for the rapidly growing preterm infant to match the accumulation that should have taken place in utero and to permit normal bone mineralization. Rickets of prematurity may present clinically between the 6th and 12th postnatal week. The clinical diagnosis may be confirmed using simple biochemical tests. Inadequate mineral substrate intake, particularly of phosphorus, is the most common cause, although a delay in the maturation of the renal enzyme, 1-alpha hydroxylase, with low plasma concentrations of 1,25-dihydroxyvitamin D, may also occur. The biochemical response to treatment can be determined by documenting a fall in plasma alkaline phosphatase activity and a rise in plasma phosphate concentration and urinary phosphate excretion.

Spontaneous resolution of bone mineral depletion in preterm infants

Fifteen preterm infants and 17 born at full term whose gestational ages ranged from 25 to 34 weeks and 38 to 42 weeks, respectively, were examined initially at postconceptional ages ranging from 38 to 44 weeks and subsequently at 46 to 71 weeks. Each examination included measurement of bone mineral content of the mid-forearm by single photon absorptiometry. For the preterm group, the mean (SD) value of bone mineral content at the first examination was 109.0 (27.6) mg/cm and was significantly lower than the corresponding value of 194.4 (19.6) mg/cm for the whole full term group. The mean subsequent rate of mineral accretion in the preterm group was 8.70 (4.60) mg/cm/week, the mean individual duration of observation being 9.7 weeks. Rate of mineral accretion for the full term group was independent of the duration of observation and averaged 1.60 (2.20) mg/cm/week. The difference between mean values of rate of mineral accretion in the preterm and full term groups was highly significant. Our results show that there is a phase of rapid mineral accretion starting at 40 weeks' postconception in preterm infants that substantially reduces the perinatal mineralisation deficit.

Calcium and phosphorus solubility in neonatal intravenous feeding solutions

The limited solubility of calcium and phosphorus in standard parenteral nutrition formulations has restricted the ability to provide sufficient minerals to preterm infants to prevent substrate deficient metabolic bone disease. We determined the solubility limits of calcium and phosphorus in a total of 160 formulations under carefully controlled conditions. By increasing the concentrations of dextrose, amino acids, and by using Addiphos instead of 8.7% dipotassium hydrogen phosphate as the phosphorus source, higher concentrations of both calcium and phosphorus were held in solution. This should permit the delivery of increased concentrations of these minerals at rates which approximate fetal accretion.

High alkaline phosphatase activity and growth in preterm neonates

In a study on 857 infants born preterm, high peak plasma alkaline phosphatase activity was independently related to slower growth rate in the neonatal period, and to a highly significant reduction in attained length at 9 months and 18 months post term. At 18 months the deficit in body length associated with peak neonatal plasma alkaline phosphase activity of 1200 IU/l or more was 1.6 cm (95% confidence interval 0.9 to 2.3 cm) after adjusting for confounding factors. The strength and magnitude of this association between high plasma alkaline phosphase activity and body length was greater than that for any other factor identified, including the infant's sex and the presence of fetal growth retardation. Data are presented that support the view that the high plasma alkaline phosphatase activity reflected early bone mineral substrate deficiency resulting in metabolic bone disease. We speculate that even silent early bone disease may interfere with the control of subsequent linear growth and emphasise the potential importance of providing preterm infants, especially those fed human milk, with adequate substrate for bone mineralisation.

Serum vitamin D metabolites in very low birth weight infants with and without rickets and fractures

Seventy-one very low birth weight (less than or equal to 1500 gm) infants were studied to determine the sequential changes in serum vitamin D metabolite concentrations between infants with and without radiographically documented rickets, fractures, or both (R/F). Usual intake of vitamin D included 20 IU/kg/day from parenteral nutrition or 400 IU/day supplementation with enteral feeding. Radiographs of both forearms and serum samples were obtained at 3, 6, 9, and 12 months. Twenty-two infants had R/F. At 3 months, significantly lower mean (+/- SEM) serum phosphorus levels (4.5 +/- 0.4 vs 6.1 +/- 0.2 mg/dl), higher 1,25-dihydroxyvitamin D (1,25-[OH]2D) concentrations (96 +/- 5 vs 77 +/- 4 pg/ml), and higher free 1,25-(OH)2D index (1,25-[OH]2D:vitamin D binding protein ratio; 5.2 +/- 0.3 x 10(5) vs 4.0 +/- 0.2 x 10(5] were found in the R/F group. These values returned to normal and were similar between groups on subsequent measurements. Serum calcium, magnesium, and 25-hydroxyvitamin D (25-OHD) concentrations were normal and similar between groups. In both groups, serum vitamin D binding concentrations increased initially but remained stable and normal beyond 6 months. We conclude that in very low birth weight infants with R/F, the vitamin D status (as indicated by serum 25-OHD concentrations) is normal, and that lowered serum phosphorus levels, higher serum 1,25-(OH)2D levels, and a higher free 1,25-(OH)2D index support the thesis that mineral deficiency (especially of phosphorus) may be important in the pathogenesis of R/F in small preterm infants.

Effect of mineral supplementation of human milk on bone mineral content and trace element metabolism

We studied the effect of feeding mineral fortified human milk to preterm infants (birth weight less than or equal to 1500 gm). Serum concentrations of calcium, magnesium, phosphorus, zinc, cooper, alkaline phosphatase, and parathyroid hormone were determined, and bone mineral content was measured, in infants fed unfortified human milk (group 1), fortified human milk (group 1), fortified human milk (group 2), and a "humanized," mineral-enriched premature infant formula (group 3). Serum calcium, magnesium, phosphorus, zinc, copper, and parathyroid hormone concentrations did not differ significantly among the groups studied. Serum alkaline phosphatase concentrations increased significantly only in the infants fed unfortified human milk, and bone mineral content in this group was significantly lower than in formula-fed infants.

Bone mineral content of infants fed soy-based formula

We compared the results of two studies that measured the bone mineral content (BMC) of 57 infants fed soy-based formula and 27 infants fed human milk or cow milk-based formula at various ages from 2 weeks to 1 year. In a study by Chan et al., the BMC of 40 white infants fed soy-based formula and 10 infants (of unstated race) fed human milk was measured at 2 weeks and at 2 and 4 months of age. The infants fed soy-based formula also had BMC measured at 6 and 12 months; the BMC of these infants was compared to the BMC of human milk-fed historical control subjects. The BMC was similar at 2 weeks in both groups but was lower in infants fed soy-based formula than in human milk-fed infants at 2 and 4 months. The BMC was similar in historical control subjects fed human milk and in soy formula-fed infants at 6 and 12 months. In the Steichen-Tsang study, the BMC of 17 soy formula-fed infants and of 17 white infants fed cow milk-based formula was measured at 6 weeks and at 3, 6, and 12 months of age. The BMC was similar at 6 weeks in both groups but was lower in infants fed soy-based formula than in those fed cow milk-based formula at 3, 6, and 12 months. The BMC of the historical control group fed human milk and of the soy formula-fed infants was also similar. In the first year of life, the BMC of infants fed soy formula and those fed human milk appears to be similar, especially after 6 months of age. However, the BMC of infants so fed may be lower than that of infants fed cow milk-based formula.

Aluminum and bone disorders: with specific reference to aluminum contamination of infant nutrients

Aluminum (Al) impairment of bone matrix formation and mineralization may be mediated by its direct effect on bone cells or indirectly by its effect on parathyroid hormone and calcium metabolism. Its toxic effects are proportional to tissue Al load. Al contamination of nutrients depends on the amount of Al present naturally in chemicals or from the manufacturing process. Intravenous calcium, phosphorus, and albumin solutions have high Al (greater than 500 micrograms/L), whereas crystalline amino acid, sterile water, and dextrose water have low Al (less than 50 micrograms/L) content. Enteral nutrients including human and whole cow milk have low Al, whereas highly processed infant formulas with multiple additives, such as soy formula, preterm infant formula, and formulas for specific disorders are heavily contaminated with Al. Healthy adults are in zero balance for Al. The gastrointestinal tract excludes greater than 95% of dietary Al, and kidney is the dominant organ for Al excretion. However, even with normal renal function, only 30-60% of an Al load from parenteral nutrition is excreted in the urine, resulting in tissue accumulation of Al. The risk for Al toxicity is greatest in infants with chronic renal insufficiency, recipients of long term parenteral nutrition, i.e., no gut barrier to Al loading, and preterm infants with low Al binding capacity. The rapid growth of the infant would theoretically potentiate Al toxicity in all infants, although the critical level of Al loading causing bone disorders is not known. To minimize tissue burden, Al content of infant nutrients should be similar to "background" levels, i.e., similar to whole milk (less than 50 micrograms/L).

Vitamin D metabolism, mineral homeostasis, and bone mineralization in term infants fed human milk, cow milk-based formula, or soy-based formula

The purpose of this study was to evaluate mechanisms of mineral homeostasis and mineralization in term infants with recommended vitamin D intakes. Infants fed human milk (nine), cow milk-based formula (11), or soy-based formula (11) were studied at 2 weeks and at 2, 4, 6, 9, and 12 months of age. While receiving 400 IU of vitamin D, all infants maintained serum vitamin D concentrations higher or equal to normal adult concentrations, and serum 25-hydroxyvitamin D levels were maintained at or above normal adult levels. Serum 1,25-dihydroxyvitamin D concentrations were higher than those of adults in the formula-fed but not in the human milk-fed infants. Serum calcium and phosphorus values were similar in all groups; however, urine phosphorus excretion and urine calcium excretion were adjusted to intakes. Serum parathyroid hormone values were normal in all groups. Bone mineral content significantly increased with age similarly in all groups; however, an apparent plateau occurred at 6 months of age in all groups. Bone width steadily increased with age. Taken as a whole, these data suggest that the vitamin D-sufficient term infant fed human milk, cow milk-based formula, or the soy-based formula studied can regulate mineral metabolism within acceptable physiologic limits to attain similar levels of serum minerals and bone mineral content.

Phosphorus deficiency syndrome in very low birth weight infants

Inadequate dietary phosphorus intake is a contributing factor to the occurrence of metabolic bone disease in very low birth weight infants. This article reviews the clinical presentation and the pathophysiology of the phosphorus deficiency syndrome in premature infants. Recommendations for therapy and prevention of phosphorus deficiency are presented.

Calcium homeostasis in premature infants and treatment of early hypocalcaemia by 1,25-dihydroxycholecalciferol

We studied calcium homeostasis and the serum calcium response to oral 1,25-dihydroxycholecalciferol [1,25 (OH)2D3] at a low pharmacological dosage of 0.1 microgram/kg daily in 14 early hypocalcaemic asymptomatic neonates. Seven hypocalcaemic neonates were not treated. In hypocalcaemic neonates serum PTH levels were normal, the urinary C-AMP response after PTH stimulation was poor and plasma 1,25 (OH)2D3 was low. Treatment with 1,25(OH)2D3 resulted in a rapid increase of serum calcium. The increase was more rapid in neonates treated with 1,25(OH)2D3 than in untreated subjects. A similar result was obtained in one of a pair of identical twins. These results suggest that a low dose of 1,25(OH)2D3 is effective in treating neonatal hypocalcaemia. However, the response was delayed for 48 h. The reason for this delay is not clear.

Bone mineralization and growth in term infants fed soy-based or cow milk-based formula

The purpose of this study was to evaluate the adequacy of a soy protein-based formula versus a cow milk protein-based formula for body growth and skeletal mineralization in the first year of life. Thirty-six healthy, term, appropriate for gestational age infants were assigned randomly and prospectively to one of two feeding groups and observed longitudinally over the first year of life. Group 1 infants (n = 18) were fed soy protein isolate-based formula (Isomil with Iron); group 2 infants (n = 17) were fed a cow milk protein-based formula (Similac with Iron). All infants were given the formula within the first 24 hours of life, and were fed the study formula through the first year of life. Weight, length, and head circumference were recorded; bone mineral content (BMC) and bone width (BW) were measured at one-third distal length (midshaft) of the left radius and ulna during the first 18 days of life, and again at 6 weeks, and 3, 6, 9, and 12 months postnatally. Baby food was provided to all infants, and except for type of formula, food intake was similar for all infants. Weight, length, and head circumference were normal in all infants and not different between groups. BMC and BMC/BW were similar for both groups at entry into the study. Group 1 infants had significantly lower BMC and BMC/BW at 3, 6, 9, and 12 months of age (P less than 0.05 to P less than 0.0001) compared with group 2 infants, but their values were similar to those in previously studied infants receiving human milk with vitamin D supplementation. The long-term implication of differences in bone mineralization in early infancy for long-term skeletal mineralization remains to be determined.

Radiological rickets in extremely low birthweight infants

Forty-eight infants of birthweight less than 1000 g who survived for more than 28 days, had wrist X-rays to prospectively determine the incidence of radiological rickets. Twelve infants (25%) had normal X-rays throughout, 10 infants (21%) showed osteopenia and 26 infants (54%) had classical changes of rickets of which 8 (17% of the total) had spontaneous fractures. There was poor correlation between peak values of serum alkaline phosphatase and the radiological changes.

Plasma alkaline phosphatase activity and its relation to rickets in pre-term infants

Sequential measurements of plasma alkaline phosphatase activity were made in 84 pre-term infants delivered before 38 weeks gestation. In 67% of infants, without evidence of rickets but in whom three or more measurements were made and the peak activity was less than 10 times the adult reference range, the activity rose to a peak and declined to previous levels, or lower. The time taken for these changes varied greatly. The range of values was inspected at each week of age, and in all but six cases the level did not exceed 10 times the upper limit of the adult reference range. Three infants had radiological evidence of rickets, and of the six cases in whom higher levels were found, only one had radiological evidence of rickets; the remainder did not. It is recommended that in the latter, the high plasma alkaline phosphatase activity should be regarded as evidence of subclinical bone disease.

Bone cortical mass in newborn infants: a comparison between standards in the femur and humerus

The total bone width (T) and medullary width (M) of the humerus and femur of 216 and 138 Nigerian newborn infants, respectively, were measured in order to determine the normal standards for cortical bone mass in the newborn. The cortical width (C), cortical area (CA), and percentage cortical area (PCA) were calculated for each bone and correlated with gestational age and birth weight. In both the femur and humerus, the values of the cortical measurements were higher in males. The strongest correlation coefficients were obtained between T(0.84), C(0.79), and CA(0.84) and birth weight in the humerus. The correlation with gestational age was, however, similar in both bones. The values of humeral cortical width (C) obtained in this study is less than had been reported in North American white newborn infants. Cortical measurements of the humerus, which is invariably included in the newborn chest radiograph, is a more reliable method of evaluating the status of bone mineralisation than the femur.