title: Seasonal differences in serum vitamin D binding protein in exclusively breast-fed infants: negative relationship to sunshine exposure and 25-hydroxyvitamin D.
abstract: Vitamin D binding protein (DBP) is the major carrier for vitamin D and its metabolites in serum. DBP increases in pregnancy and decreases in cirrhosis; no seasonal variation has been reported in adults. We observed significant seasonal differences in 41 exclusively breast-fed infants who were less than 6 months of age. Winter DBP concentrations exceeded summer DBP concentrations: 398 +/- 22 versus 297 +/- 20 micrograms/ml (mean +/- SEM). The mean concentration for spring and fall was 329 +/- 25 micrograms/ml. Maternal DBP concentrations did not differ by season. A sunshine exposure score, previously verified, was used to document time and body surface exposed to the sun. DBP was inversely related to sun exposure (r = -0.46, p = 0.005). Infant DBP was significantly and negatively correlated with 25-hydroxyvitamin D concentrations (r = - 0.38, p = 0.02). We speculate that serum DBP fluctuations are a response to varying vitamin D needs: increased serum DBP occurs in low vitamin D status to maximize uptake of vitamin D from skin.
mesh_terms: D001942:Breast Feeding; D005260:Female; D006801:Humans; D006887:Hydroxycholecalciferols / Q000097:blood; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D012621:Seasons; D013472:Sunlight; D014809:Vitamin D-Binding Protein / Q000097:blood*
chemical_list: D006887:Hydroxycholecalciferols; D014809:Vitamin D-Binding Protein