CALCIUM AND BONE MINERAL METABOLISM IN CHILDREN WITH CHRONIC ILLNESSES

Bone Health in School Age Children: Effects of Nutritional Intake on Outcomes

The maximum rate of bone mass accumulation is during early adolescence. As such, a focus on optimizing mineral nutrition in school age children, defined here as approximately 5 to 15 years of age, is crucial to minimize the risk of bone loss that occurs later in life leading to osteoporosis and fractures. Optimizing bone mass in this age group requires attention to an overall healthy diet including adequate calcium, phosphorus, magnesium, and vitamin D. Special concerns may exist related to children who follow a restricted diet such as a vegan diet, those with intolerance or allergies to dairy, and those with chronic health conditions including young adolescents with eating disorders. Public policy messages should focus on positive aspects of bone health nutrition in this age group and avoid overly specific statements about the exact amounts of foods needed for healthy bones. In this regard, dietary recommendations for minerals vary between North America and Europe and these are higher than the values that may be necessary in other parts of the world. The management of many children with chronic illnesses includes the use of medications that may affect their bone mineral metabolism. Routine lab testing for bone mineral metabolism including the serum 25-hydroxyvitamin D level is not indicated, but is valuable for at-risk children, especially those with chronic illnesses.

The role of delayed bone age in the evaluation of stature and bone health in glucocorticoid treated patients with Duchenne muscular dystrophy

Background

Low bone mineral density and an increased risk of appendicular and vertebral fractures are well-established consequences of Duchenne muscular dystrophy (DMD) and the risk of fractures is exacerbated by long-term glucocorticoid treatment. Monitoring of endocrine and skeletal health and timely intervention in at-risk patients is important in the management of children with DMD.

Methods

As part of the Norwegian Duchenne muscular dystrophy cohort study, we examined the skeletal maturation of 62 boys less than 18 years old, both currently glucocorticoid treated (n = 44), previously treated (n = 6) and naïve (n = 12). The relationship between bone age, height and bone mineral density (BMD) Z-scores was explored.

Results

The participants in the glucocorticoid treated group were short in stature and puberty was delayed. Bone age was significantly delayed, and the delay increased with age and duration of treatment. The difference in height between glucocorticoid treated and naïve boys was no longer significant when height was corrected for delayed skeletal maturation. Mean BMD Z-scores fell below − 2 before 12 years of age in the glucocorticoid treated group, with scores significantly correlated with age, duration of treatment and pubertal development. When BMD Z-scores were corrected for by retarded bone age, the increase in BMD Z-scores was significant for all age groups.

Conclusion

Our results suggest that skeletal maturation should be assessed in the evaluation of short stature and bone health in GC treated boys with DMD, as failing to consider delayed bone age leads to underestimation of BMD Z-scores and potentially overestimation of fracture risk.

Using stable isotope tracers to study bone metabolism in children

Skeletal mineralization is initiated in utero and continues throughout childhood and adolescence. During these key periods of the life cycle, calcium retention must increase significantly to provide sufficient mineral for bone deposition and skeletal growth. Stable calcium isotopes have served as a fundamental tool to non-invasively characterize the dynamic changes in calcium physiology that occur from infancy through adolescence. These approaches have helped define the dynamics of calcium absorption and utilization in healthy children and in children with chronic diseases. As data in this area have accumulated, new areas of emphasis are beginning to characterize the determinants of variability in mineral retention, the genetic determinants of bone turnover and calcium flux and the impact of the gut microbiome on whole body and niche specific calcium dynamics. Advances in these areas will help define calcium utilization in paediatric populations and provide information that may be useful in maximizing bone acquisition across this critical phase of the life cycle.

Factors Determining Bone Mineral Density in Patients with Biliary Atresia after a Successful Kasai Operation

BACKGROUND

Hepatic osteodystrophy is a common complication in patients with chronic liver disease, however, bone mineral status in patients with biliary atresia has rarely been investigated.

METHODS

Twenty-nine children with biliary atresia were enrolled in our study and their demographic data, bone mineral density (BMD) of lumbar spine and bilateral femoral neck, and biochemical parameters were measured and analyzed.

RESULTS

The majority of our patients had osteopenia or osteoporosis over at least one part of the skeleton although none had jaundice. Instead of T helper 1 cell cytokine, interleukin (IL)-4 had a significant negative correlation with BMD of the right femoral neck (β = -0.251, p = 0.027) and left femoral neck (β = -0.299, p = 0.012) independently by multiple linear regression analysis.

CONCLUSION

We conclude that chronic inflammation with increased expression of IL-4 may be an important factor for compromised bone health in patients with biliary atresia.

[Recommended intake of calcium and vitamin D: positioning of the Nutrition Committee of the AEP]

Both calcium and vitamin D are essential nutrients with a crucial role in bone health, although in recent years there has been much controversy about the contributions required from both molecules to ensure adequate health. For vitamin D, in a short time, we have seen how it has gone from a recommendation of 400 IU daily, to 200 IU and again to 400 IU, with some statements that not only its influence on skeletal tissue has been taken into account, but also on the development of chronic diseases, which has led to new expectations. Our goal is to provide an update to paediatricians on this issue and propose recommendations for intake in the light of the latest information. For vitamin D the Committee proposes an intake of 400 IU/day in children under 1 year and 600 IU/day after that age.

Insights into bone health in Duchenne muscular dystrophy

Poor bone health is a significant problem for patients with Duchenne muscular dystrophy (DMD), a progressive, disabling disease. Although the primary focus of DMD disease pathogenesis is degeneration of striated muscle, impairment of bone health likely has a role in the disease that has only been superficially examined to date. Deficiency of bone mineral density and increased incidence of bone fractures are well-recognized clinical components of the DMD phenotype. Furthermore, therapy with corticosteroids, an approved treatment for DMD that prolongs ambulation, may have multiple effects on bone health in DMD patients. This review examines the evidence in preclinical models and in human DMD disease that provides insight into the role performed by bone in the disease pathogenesis and phenotype of DMD. The information reviewed here points toward the need for mechanistic and therapeutic studies to optimize bone health in DMD patients.

Effects of 1alpha,25-dihydroxyvitamin D3 on transporters and enzymes of the rat intestine and kidney in vivo

1alpha,25-Dihydroxyvitamin D3 (1,25(OH)2D3), the natural ligand of the vitamin D receptor (VDR), was found to regulate bile acid related transporters and enzymes directly and indirectly in the rat intestine and liver in vivo. The kidney is another VDR-rich target organ in which VDR regulation on xenobiotic transporters and enzymes is ill-defined. Hence, changes in protein and mRNA expression of nuclear receptors, transporters and enzymes of the rat intestine and kidney in response to 1,25(OH)2D3 treatment (0 to 2.56 nmol/kg/day intraperitoneally in corn oil for 4 days) were studied. In the intestine, protein and not mRNA levels of Mrp2, Mrp3, Mrp4 and PepT1 in the duodenum and proximal jejunum were induced, whereas Oat1 and Oat3 mRNA were decreased in the ileum after 1,25(OH)2D3 treatment. In the kidney, VDR, Cyp24, Asbt and Mdr1a mRNA and protein expression increased significantly (2- to 20-fold) in 1,25(OH)2D3-treated rats, and a 28-fold increase of Cyp3a9 mRNA but not of total Cy3a protein nor Cyp3a1 and Cyp3a2 mRNA was observed, implicating that VDR played a significant, renal-specific role in Cyp3a9 induction. Additionally, renal mRNA levels of PepT1, Oat1, Oat3, Ostalpha, and Mrp4, and protein levels of PepT1 and Oat1 were decreased in a dose-dependent manner, and the approximately 50% concomitant reduction in FXR, SHP, HNF-1alpha and HNF-4alpha mRNA expression suggests the possibility of cross-talk among the nuclear receptors. It is concluded that the effects of 1,25(OH)2D3 changes are tissue-specific, differing between the intestine and kidney which are VDR-rich organs.

Drug-induced nutrient deficiencies

Good clinical care extends beyond mere diagnosis and treatment of disease to appreciation that nutrient deficiencies can be the price of effective drug therapy. The major risk factors for developing drug-induced nutrient deficiencies are lack of awareness by the prescribing physician and long duration of drug therapy. The field of pharmacogenomics has potential to improve clinical care by detecting patients at risk for complications from drug therapy. Further improvements in patient safety rely on physicians voluntarily reporting serious suspected adverse drug reactions.

Bone health in a nonjaundiced population of children with biliary atresia

Objectives. To assess bone health in a cohort of nonjaundiced children with biliary atresia (BA) and the effect of growth and development on bone outcomes. Methods. Children ages one to eighteen years receiving care from Children's Hospital of Philadelphia were recruited. Each child was seen once and assessed for growth, pubertal development, concurrent medications, bilirubin, ALT, albumin, vitamin D status, bone mineral density (BMD), and bone mineral content (BMC) of the lumbar spine and whole body. Results. BMD declined significantly with age, and upon further analysis with a well-phenotyped control cohort, it was found that BMC was significantly decreased for both lumbar spine and whole body, even after adjustment for confounding variables. An age interaction was identified, with older subjects having a significantly greater impairment in BMC. Conclusions. These preliminary results demonstrate that children with BA, including those without jaundice, are likely to have compromised bone health even when accounting for height and puberty, which are common confounding factors in chronic disease. Further investigation is needed to identify the determinants of poor bone mineral status and to develop strategies to prevent osteoporosis later in life.

Bone density interpretation and relevance in Caucasian children aged 9-17 years of age: insights from a population-based fracture study

The interpretation of bone density measurement in children is difficult due to a number of factors including rapid change in body size and uncertain clinical significance of bone density in children. This study asked two questions. (1) Is there a preferred bone density measurement site or type for fracture risk in children? (2) What is the best way to interpret bone density in children? This population-based case control study included 321 upper limb fracture cases and 321 class- and sex- matched randomly selected controls. Bone density at the hip, spine, and total body (including the arm) was measured by a Hologic QDR2000 densitometer (Waltham, MA) and examined as bone area (BA), bone mineral content (BMC), bone mineral density (BMD), bone mineral apparent density (BMAD), and BMC/lean mass (BMCLM). The only dual-energy X-ray absorptiometry (DXA) variables that were consistently associated with fracture risk in both boys and girls were spine BMD and BMAD for total upper limb fractures, and spine and hip BMAD for wrist and forearm fractures. No significant associations were observed for BA and BMCLM and inconsistent associations for BMC and other BMD sites. Five-yr fracture risk varied from 15-24% depending on site and gender in a child with a Z-score of -3. In the controls, all DXA variables were associated with age, height, and weight, but the weakest associations were with BMAD. In conclusion, in this study the spine BMAD had the strongest and most consistent association with upper limb fracture risk in children. The associations with age and body size imply that age specific Z-scores will be the most convenient for interpretation of DXA measures in children. Five-yr wrist and forearm fracture risk has potential as a clinical endpoint of immediate relevance.

Calcium Supplementation during Childhood: Long-term Effects on Bone Mineralization

Calcium supplementation has been shown to increase bone mineralization in children and adolescents. However, catch-up mineralization later in puberty appears likely if intake is consistent with usual average intakes in the United States. Ultimately, individualized risk assessment will be developed based on genetic and lifestyle factors that can be used to guide optimal calcium intake during childhood.