Laura S. Hillman

Correcting vitamin D insufficiency improves insulin sensitivity in obese adolescents: a randomized controlled trial

BACKGROUND Obese adolescents are at a greater risk of vitamin D deficiency because vitamin D is thought to be sequestered by excess adipose tissue. Poor vitamin D status has been associated with a higher prevalence of the metabolic syndrome, type 2 diabetes, or both in adults and adolescents. OBJECTIVE The objective was to determine in obese adolescents the efficacy and safety of 4000 IU vitamin D3/d and whether subsequent increased circulating concentrations of 25-hydroxyvitamin D [25(OH)D] are associated with improved markers of insulin sensitivity and resistance and reduced inflammation. DESIGN Obese adolescent patients [n = 35; mean ± SD age: 14.1 ± 2.8 y; BMI (in kg/m(2)): 39.8 ± 6.1; 25(OH)D: 19.6 ± 7.1 ng/mL] were recruited from the University of Missouri Adolescent Diabetes and Obesity Clinic and were randomly assigned to receive either vitamin D3 (4000 IU/d) or placebo as part of their standard care. Anthropometric measurements, inflammatory markers (IL-6, TNF-α, C-reactive protein), adipokines (leptin, adiponectin), fasting glucose, fasting insulin, and HOMA-IR values were measured at baseline and at 2 follow-up visits (3 and 6 mo). RESULTS After 6 mo, there were no significant differences in BMI, serum inflammatory markers, or plasma glucose concentrations between groups. Participants supplemented with vitamin D3 had increases in serum 25(OH)D concentrations (19.5 compared with 2.8 ng/mL for placebo; P < 0.001), fasting insulin (-6.5 compared with +1.2 μU/mL for placebo; P = 0.026), HOMA-IR (-1.363 compared with +0.27 for placebo; P = 0.033), and leptin-to-adiponectin ratio (-1.41 compared with +0.10 for placebo; P = 0.045). Inflammatory markers remained unchanged. CONCLUSION The correction of poor vitamin D status through dietary supplementation may be an effective addition to the standard treatment of obesity and its associated insulin resistance. This trial was registered at clinicaltrials.gov as NCT00994396.

Vitamin D metabolism and bone mineralization in children with juvenile rheumatoid arthritis

OBJECTIVE To examine bone mineralization and bone mineral content in a cross-sectional population of children with juvenile rheumatoid arthritis (JRA). METHODS Bone mineral content was measured by single-photon absorptiometry in 44 children with JRA and 37 control children. Serum concentrations of minerals, vitamin D, parathyroid hormone, osteocalcin, bone alkaline phosphatase, and tartrate-resistant acid phosphatase, and urinary concentrations of minerals, were determined. RESULTS Bone mineral content was decreased in children with JRA. Significantly lower concentrations of osteocalcin (7.4 +/- 3.4 vs 12.5 +/- 2.5 micrograms/L) and bone alkaline phosphatase (78.8 +/- 36.4 vs 123.0 +/- 46.0 IU/L) suggested reduced bone formation; lower levels of tartrate-resistant acid phosphatase (10.3 +/- 4.1 vs 14.4 +/- 5.8 IU/L) and a lower urinary calcium/creatinine ratio (0.07 +/- 0.06 vs 0.12 +/- 0.09) suggested decreased bone resorption. The serum calcium concentration was significantly lower (9.3 +/- 1.0 vs 10.0 +/- 0.4 mg/dl), as was the parathyroid hormone concentration (19.8 +/- 8.6 vs 26.7 +/- 9.3 ng/L); 1,25-dihydroxyvitamin D values (30.1 +/- 10.5 vs 30.4 +/- 9.3 pg/ml) were normal. CONCLUSION These data suggest that decreased mineralization in JRA is related to low bone turnover; parathyroid hormone and 1,25-dihydroxyvitamin D levels may be inappropriately normal for the decreased serum calcium concentration in children with JRA.

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.

Mineral and vitamin D adequacy ininfants fed human milk or formula between 6 and 12 months of age

During the latter half of an infants first year, adequate mineral and vitamin D intakes may be important not only for the prevention of rickets but also for the attainment of optimal adult peak bone mass. Ingestion of 400 IU vitamin D per day, either as a supplement or contained in formula or table milk, will result in normal serum concentrations of vitamin D,25-hydroxyvitamin D, and 1,25-dihydroxyvitamin D. Human milk from a vitamin D-sufficient mother provides a marginal amount, less than 100 IU/L/day of total vitamin D activity from the vitamin D and 25-hydroxyvitamin D. Infants exclusively fed human milk of vitamin D-deficient mothers, who do not receive additional vitamin D or adequate exposure to sunlight, are at significant risk for vitamin D-deficiency rickets. The low concentration of phosphorus in human milk is adequate for most term infants but probably compounds any vitamin D deficiency. Intake of phosphorus from formula or table milk is more than adequate, and the addition of baby foods increases this minerals intake to generous levels. Calcium is well absorbed and adequate in human milk if vitamin D is sufficient, but concern exists about calcium intake from infant formulas for this older group. My colleagues and I have conducted studies of bone mineral content and mineral homeostasis in term infants fed human milk (300 mg/L calcium), standard cow milk formula (440/mg/L calcium), or a soybean formula (600 mg/L calcium); our findings suggest that all three types of feedings provided comparable bone mineralization and normal indicators of mineral homeostasis. Mean calcium retentions at 6 months, 9 months, and 12 months in all three groups were between 138 and 205 mg/day, substantially more than the 130 mg/day estimated to be needed from body composition data. Estimates for phosphorus were similarly generous. The questions of whether higher calcium intakes will result in further increases in bone mineral content and of the effect of beikost on calcium absorption from different milks require further study.

Percent True Calcium Absorption, Mineral Metabolism, and Bone Mineralization in Children With Cystic Fibrosis : Effect of Supplementation With Vitamin D and Calcium

To assess whether percent true calcium absorption (α) is normal in children with cystic fibrosis (CF) and to assess whether supplementation with 2,000 IU vitamin D3, 1 g calcium, or both will alter α, mineral metabolism, and/or bone mass in children with CF.

Measurement of true absorption, endogenous fecal excretion, urinary excretion, and retention of calcium in term infants by using a dual-tracer, stable-isotope method.

A dual-tracer, stable-isotope method was used to measure the percentage of true calcium absorption (alpha), true calcium absorption rate (Va), endogenous fecal calcium excretion rate (Vf), urinary calcium excretion rate (Vu), and calcium retention rate (Vr). Twenty-seven infants with a mean gestation of 30.6 +/- 1.7 weeks and a mean birth weight of 1.4 +/- 0.21 kg were studied at 2 or 3 weeks of age, or both, during feedings of human milk (HM), fortified human milk (HMF), and commercially available formula (20 or 24 calories per ounce) for premature infants (EPF-20/780 and EPF-24/940) (part 1 of our study). Of 13 additional infants with a mean (+/- SD) birth weight of 1.26 +/- 0.25 kg and gestation of 29.6 +/- 2.5 weeks, 11 completed a crossover-design study at 2 and 3 weeks of age, receiving two identical formulas containing calcium, 940 mg/L, and phosphorus, 470 mg/L (EPF-24/940 formula) or calcium 1340 mg/L, and phosphorus, 680 mg/L (EPF-24/1340 formula) (part 2 of our study). The alpha value was higher in infants receiving HM (76.4 +/- 15.1%) or HMF (68.0 +/- 7.8%) than in those receiving EPF-20/750 formula (54.1% +/- 5.6%) or in previously reported infants fed standard formula (47.1% +/- 11.5%); those given EPF-24/940 formula had intermediate values (63.9% +/- 13.9%, part 1; 56.1% +/- 16.5%, part 2). No significant differences existed among groups for either Vu or Vf per kilogram. In the crossover study (part 2), no significant differences were seen between formulas for alpha and for Va, Vf, or Vr per kilogram. However, Vu per kilogram was significantly decreased in infants receiving the higher mineral formula (EPF-24/940: 3.6 +/- 2.3; EPF-24/1340: 2.9 +/- 2.3 mg/kg per day; p = < 0.005). With all feedings, alpha, Vu per kilogram, and Vf per kilogram were not related to gestational age, age at study, calcium intake, or each other. However, Vf per kilogram was inversely related to birth weight. Thus, alpha, Vu, and Vf appear to be independent and may be differentially affected by factors altering calcium dynamics. We conclude that increasing formula mineral content does not ensure increased retention; careful monitoring of individual infants remains indicated.

Percent true calcium absorption, mineral metabolism, and bone mass in children with arthritis: Effect of supplementation with vitamin D3 and calcium

OBJECTIVE To assess whether percent true calcium absorption (alpha) is normal and whether supplementation with placebo, vitamin D3 (2,000 IU/day), calcium (1,000 mg/day), or vitamin D3 plus calcium improves alpha, mineral metabolism, or bone mass accrual in children with arthritis. METHODS Eighteen children received all 4 treatments, each for 6 months, in 4 different, randomly assigned orders. Changes in levels of 25-hydroxyvitamin D (25[OH]D), 1,25-dihydroxyvitamin D (1,25[OH]2D), parathyroid hormone, bone turnover markers, and minerals and in bone mineral content were measured. Calcium absorption was determined with a dual stable isotope method using 48Ca administered intravenously and 46Ca administered orally, and measuring 48Ca, 46Ca, and 42Ca in a 24-hour urine specimen by high-resolution inductively coupled plasma mass spectroscopy. Wilcoxons signed rank test was used both to identify significant change over the treatment period with a given regimen and to compare change with an experimental treatment versus change with placebo. RESULTS Percent true calcium absorption was in the lower-normal range and did not differ by treatment (mean+/-SD 28.3+/-20.2% with placebo, 26.1+/-12.1% with calcium, 19.2+/-11.7% with vitamin D3, and 27.1+/-16.5% with vitamin D3 plus calcium). With vitamin D3 and vitamin D3 plus calcium treatment, 25(OH)D levels were increased and 1,25(OH)2D levels were maintained. Serum calcium levels were increased only with vitamin D3 and vitamin D3 plus calcium treatment. Levels of bone turnover markers and increases in bone mineral content did not differ by treatment. CONCLUSION The findings of this study indicate that percent true calcium absorption is low-normal in children with arthritis. Vitamin D3 at 2,000 IU/day increases serum 25(OH)D and calcium levels but does not improve bone mass accretion. Calcium at 1,000 mg/day also failed to improve bone mass.

The Effects of Calcium Supplementation, Duration of Lactation, and Time of Day on Concentrations of Parathyroid Hormone-Related Protein in Human Milk: A Pilot Study

This pilot study reports parathyroid hormone-related protein (PTHrP) in milk from 14 women (placebo=6, calcium=8) over the duration of lactation. Milk samples collected 0 to 250 days postpartum were assayed for PTHrP by a two-site immunoradiometric assay. PTHrP concentrations were significantly lower in colostrum 0-4 days postpartum (5,080 + 1575 pmoll L) than at 7-60 days postpartum (11,863 + 1528-14,213 + 1574 pmolIL); concentrations did not differ between calcium and placebo groups. A suggestive diurnal variation was seen in two women who collected milk samples over 48 continuous hours. Confounding factors related to milk synthesis and milk sampling contribute to variability in PTHrP concentrations.

Mineral content of calcified tissues in cystic fibrosis mice.

Although abnormal hard tissue mineralization is a recognized complication of cystic fibrosis (CF), the pathogenesis leading from the defective cystic fibrosis transmembrane conductance regulator (CFTR) protein is poorly understood. We hypothesized that CFTR plays a direct role in the mineralization of bone and teeth and tested the hypothesis using CF mouse models [CFTR(−) mice]. In vivo measurements by dual-emission X-ray absorpitometry (DEXA) indicated that bone mineral density (BMD) was reduced in CF mice as compared to gender-matched littermates. However, no change was evident after correction of BMD for the covariant of body weight. The latter finding was confirmed in isolated femurs and nasal bones by standard dry-ashing and instrumental neutron activation analysis (INAA). INAA of the continuously growing hypsodont incisor teeth from CFTR(−) mice revealed reduced Ca and normal P in the enamel layer—a finding consistent with changes in the deciduous teeth of CF children. Interestingly, enamel fluoride was increased in the CFTR(−) incisors and may associate with abnormal enamel crystallite formation. The iron content of the incisor enamel was reduced, explaining the loss of yellow pigmentation in CFTR(−) incisors. In contrast to the incisors, the mineral content of the slow-growing brachydont molar teeth was not different between CFTR(−) and CFTR(+) mice. It was concluded that CFTR does not play a direct role in the mineralization of bones or brachydont teeth in mice. Functional CFTR is apparently required for normal mineralization of the hypsodont incisors. However, multiple changes in the mineral composition of the CF incisors suggest an indirect role for CFTR, perhaps by maintaining a normal salivary environment for continuous tooth eruption.

Estrogen agonist (zeranol) treatment in a castrated male lamb model: effects on growth and bone mineral accretion.

The mechanism of estrogens action on bone mineralization in children has received little attention. Our objective was to determine the effect of time (developmentally) and duration of exposure to an estrogen agonist (zeranol) on bone growth and mineralization using a castrated male lamb model. At birth, 40 male lambs were castrated and within 14 days of birth (day = 0) they were assigned (n = 10 per group) to age‐matched control lambs (C‐AGE) or to receive a 12.5‐mg zeranol implant as follows: E‐0, implanted on days 0, 45, 90, and 135; E‐90, implanted on days 90 and 135; and E‐0,90, implanted on days 0, 90, and 135. Lambs were studied for 163 days. Serum was collected on days 28, 73, 118, 135, and 163 and analyzed for minerals (Ca, P, and Mg), markers of bone remodeling (bone alkaline phosphatase [ALP] and tartrate resistant acid phosphatase [TRAP]), 1,25‐dihydroxyvitamin D [1,25(OH)2D], growth hormone (GH), and insulin‐like growth factor I (IGF‐I). Whole‐body bone mineral content (BMC), bone mineral density (BMD), fat mass, and lean mass were determined by dual energy X‐ray absorptiometry (DEXA) on days 28, 73, 118, and 163. There was a linear increase in growth at all time points. Whole‐body BMC, weight, and lean mass of C‐AGE and E‐90 lambs were less than E‐0, and E‐0,90 lambs at all time points. Whole‐body BMD of C‐AGE and E‐90 lambs was less than E‐0 and E‐0,90 lambs at 28 days and 73 days; however, after implantation at day 90 whole‐body BMD of E‐90 lambs was similar to E‐0 and E‐0,90 lambs at day 118 and day 163 and all three were greater than C‐AGE lambs. There was no effect of treatment on calcium absorption, serum minerals, hormones, or markers of bone remodeling. We conclude from these data that treatment of growing castrated lambs with an estrogen agonist from birth augments growth, whereas delaying estrogen agonist treatment does not facilitate growth but appears to augment bone mineral accretion. We suggest these observations may have clinical relevance, and deserve consideration when treating children with delays in growth and bone mineral accretion.