Low total body bone mineral content and high bone resorption in Korean winter-born versus summer-born newborn infants.

Seasonal differences in newborn total body bone mineral content (TBBMC) have not been studied, particularly in relation to alterations in vitamin D status in winter. In vitamin D deficiency bone resorption may be high and bone mineralization low. Bone resorption may be assessed by serum cross-linked carboxyterminal telopeptide of type I collagen (ICTP) measures. Because vitamin D supplements throughout pregnancy are uncommon in Korea, we hypothesized that in Korean winter newborns, TBBMC is low and serum ICTP high from high bone resorption and low 25-hydroxyvitamin D (25-OHD) compared with those in summer newborns. Seventy-one Korean term infants were studied prospectively in summer (July through September, n = 37) versus winter (January through March, n = 34); TBBMC was measured before 3 days of age by dual-energy x-ray absorptiometry. Significant seasonal differences were found: winter newborns had 6% lower TBBMC (least squares means +/- SD; 86.7 +/- 7.7 gm vs 93.9 +/- 7.8 gm, p = 0.0002), lower cord serum 25-OHD (10.7 +/- 8 nm vs 30 +/- 15 nm, p = 0.0001) and 1,25-dihydroxyvitamin D, and higher ICTP (96.4 +/- 20.3 microg/L vs 74.8 +/- 24 microg/L, p = 0.0002) and calcium than summer newborns. TBBMC correlated with serum 25-OHD (r = 0.243, p = 0.047) and inversely with ICTP (r = -0.333, p = 0.008). We suggest that in Korea low maternal vitamin D status in winter results in marked reduction in newborn TBBMC.

Reduced serum osteocalcin and 1,25-dihydroxyvitamin D concentrations and low bone mineral content in small for gestational age infants: evidence of decreased bone formation rates.

In small for gestational age (SGA) infants, bone mineral content (BMC) is low but the reasons are unclear and the possible relationships between calcium-regulating hormones and BMC have not been studied. We hypothesized that BMC would be lower and concentrations of serum parathyroid hormone and 1,25-dihydroxyvitamin D would be higher at birth in SGA infants than in appropriate for gestational age (AGA) infants. Forty-two term SGA infants and 126 term AGA infants, matched 1:3 specifically by gestation (+/- 1 week) and birth month, were studied prospectively. The BMC of the distal one third of the radius was measured before 3 days of age by photon absorptiometry. The BMC was lower in SGA than in AGA infants. Both SGA and AGA infants had lower BMC in summer or spring than in winter; BMC differences between groups remained significant after adjustment for season (p = 0.0001). Cord serum osteocalcin and 1,25-dihydroxyvitamin D values were lower in SGA than in AGA infants. There were no differences between groups in cord serum levels of intact parathyroid hormone, 25-hydroxyvitamin D, calcium, phosphorus, and magnesium. Relationships were positive between BMC and birth weight and were inverse between BMC and intact parathyroid hormone values. We suggest that reduced uteroplacental blood flow in SGA infants may result in reduced fetal-placental production of 1,25-dihydroxyvitamin D, which results in low BMC and low serum osteocalcin values; fetal serum parathyroid hormone values may be relatively elevated because of reduced placental mineral supply.

Prospective study of vitamin D supplementation and rickets in China.

To determine whether amounts of vitamin D lower than recommended doses are effective in preventing rickets, 256 term infants from two northern and two southern cities in China were studied in a randomized trial of vitamin D supplementation (100, 200, or 400 IU/day) during the first 6 months of life. Cord blood and 6-month blood samples were collected and radiographs were obtained at 3 to 5 days and at 6 months of age. Cord serum 25-hydroxyvitamin D concentrations were lower in the north than in the south (5 vs 14 ng/ml (12.5 vs 35.0 nmol/L); p less than 0.01). Wrist ossification centers were less likely to be present at birth in the northern children than in the southern children (p = 0.009) and were more likely to be present in infants born in the fall who had higher cord serum concentrations of 25-hydroxyvitamin D (p = 0.04). Serum 25-hydroxyvitamin D concentrations were lower in northern children 6 months of age than in southern children (p = 0.005) and were higher with an increasing supplemental dosage of vitamin D (p less than 0.001), particularly in infants in the north. None of the infants had rickets at 6 months of age. Because of the low serum 25-hydroxyvitamin D concentrations, especially among infants in the north, it may be prudent to supplement the diet with vitamin D at a dose of 400 IU/day.

Randomized study of sunshine exposure and serum 25-OHD in breast-fed infants in Beijing, China.

PIP: The hypothesis that breastfed infants in Beijing, China, have low vitamin D status and that sunshine exposure increases serum 25-hydroxyvitamin D (25-OHD) concentrations was tested in a randomized prospective study involving 42 healthy infants 1-8 months of age. 24 controls were exposed to the usual amount of sunshine, while the 18 cases were provided with 2 hours of sunshine/day. All infants were being breastfed without vitamin D supplementation. Serum 25-OHD concentrations at entry into the study ranged from 3-61 ng/ml and increased with age. 3 infants in each group were diagnosed as having rickets. Serum 25-OHD concentrations did not change significantly during the 2-month study period among controls, while serum 25-OHD values increased significantly in the experimental group. Final infant serum 25-OHD concentrations correlated with ultraviolet exposure scores (p.001). The estimate of ultraviolet score needed to maintain a serum 25-OHD of 11 ng/ml was 2.4 (24 minutes/day with only the face uncovered). Rickets has been reported in as many as 18% of Chinese infants and seems to especially affect those 2-4 months of age. The fact that not all infants with rickets in this study had low 25-OHD concentrations suggests 2 possibilities: 1) not all rickets is necessarily related to a vitamin D deficiency, or 2) serum 25-OHD concentrations are not the best indicator of vitamin D status. The low serum 25-OHD concentrations in many Chinese infants may be related to low maternal milk vitamin D content resulting from the lack of vitamin D food fortification. Overall, these results suggest that the diet of breastfed Chinese infants should be supplemented with orally administered vitamin D.^ieng