R Namgung, C Lee, DG Han, ML Ho, RI Sierra, RC Tsang

Seasonal differences in newborn total body bone mineral content (TBBMC) have not been studied. Since Korean women do not usually receive vitamin D supplement during pregnancy and they may have borderline vitamin D deficiency, we theorized that in winter, low serum 25-hydroxyvitamin D (25-OHD) would result in low TBBMC in the newborn and evidence of high bone resorption. In vitamin D deficiency, bone resorption may be high: we measured serum cross-linked carboxyterminal telopeptide of type I collagen, a new bone resorption marker. 71 Korean, term weight-appropriate infants were studied prospectively in summer (July-September, n=37) vs winter (January-March, n=34): gestation (mean ± SD 38.3 ± 0.7 vs 38.3 ± 0.8 weeks) and birth weight (3327 ± 269 vs 3298 ± 313 g) were similar. TBBMC was measured < age 3 days using dual energy X-ray absorptiometry (Lunar, phantom standard CV < 2%). Significant seasonal differences were found: winter-newborns had 6% lower TBBMC than summer, even after adjusting for weight (87.3 ± 9.9 vs 93.3 ± 11.9g, P= 0.0002): TBBMC correlated with weight (r=0.661, P=0.0001). Serum ICTP (96.4 ± 20.3 vs 74.8 ± 24ng/ml, P=0.0002) and Ca were higher, 25-OHD (4.3 ± 3.2 vs 12 ± 6ng/ml, P=0.0001) and 1,25-(OH)₂D (21.4 ± 6.1 vs 30.4 ± 10.2pg/ ml) were lower, in winter vs summer. There were no differences in cord serum osteocalcin, carboxyterminal propeptide of type I procollagen (two bone formation indices), intact parathyroid hormone, P or Mg. TBBMC correlated positively with serum 25-OHD (r=0.243, P=0.047) and inversely with serum ICTP (r=-0.333, P=0.008). Thus, winter newborns had lower TBBMC, lower serum 25-OHD and higher serum ICTP vs summer: TBBMC correlated with vitamin D status and bone resorption indices. Since any seasonal effects on fetal bone are presumably effected through the mother, we suggest that lack of vitamin D supplement throughout pregnancy causes significant maternal vitamin D deficiency particularly in winter, and influences late fetal high accretion bone mineralization.