 Biochemistry Measurements - Capillary blood samples 0.5 ml will be collected at screening; but venous sampling 1.0 ml: yields 500-600 μl serum used thereafter; samples will be centrifuged 2235 x g for 20 min at 4C to obtain serum for biochemistry and buffy coat white blood cells for DNA and stored frozen at -80C until analysis. One 5 ml sample will be taken from parents at baseline fasting for measurement of serum 25OHD and buffy coat saved for future epigenetic work. For infant screening and maternal serum, total 25OHD will be measured using a dedicated auto-analyzer in the PIs laboratory 25 μl; 150 μl dead volume that is recovered, Liaison Diasorin Inc.; this assay will also be used for safety assessments at 3 and 6 mo, but is not to be used in analyzing the trial data outcomes as it does not capture all of the metabolites. Liquid chromatography tandem mass spectrometry LC-MSMS by Dr. Jones, Queens Univ. will be used to measure of 25OHD3, 3-epi- 25OHD3, and 24,25OH2D for all time-points from baseline to 36 mo. In addition, 1,25OH2D 100 μl serum will be similarly measured using an adapted LC-MSMS method. Both laboratories are certificated by the Vitamin D External Quality Assessment Scheme and will continue to participate in the National Institute of Standards and Technology quality assurance program. Blood-ionized calcium will be measured immediately using our portable unit ABL80 FLEX Radiometer Medical AS, Denmark and compared to published standards 90. Remaining sample will be used for IGF-1 20 μl using Liaison Diasorin Inc.; PTH 25 μl; Immutopics Inc CAT60-3100 and IGFBP3 20 μl; RD Systems CATSGB300 will be measured by ELISA. Sample for IGFBP3 will be pre-treated with protease inhibitors prior to storage. Plasma total calcium and phosphate 150 μl and urinary calcium and phosphate:creatinine will be measured in a spot sample collected at each visit during the trial; Beckman Coulter UniCel DxC600 autoanalyzer. We will reserve remaining sample for later measurement of C-telepeptide, propeptide of type 1 collagen P1NP as biomarkers related to bone. 