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In contrast to our hypothesis, gross motor achievements were significantly higher in infants receiving 400 IU/day vitamin D. Our findings also support longer infants being slightly delayed.

No significant correlations were observed between iCa and PTH at individual visits (p>0.2). After accounting for repeated measures, PTH decreased with increasing iCa (slope -5.25; 95% confidence intervals (CI) -8.78 to -1.73), decreased with increasing 25(OH)D (slope -0.006; 95% CI -0.009 to -0.002, and increased with later visits (6-12 months, p<0.001), CONCLUSIONS: We observed a weak negative relationship between iCa and PTH and an increase with age consistent with physiologic maturation.

The Canadian Paediatric Society (CPS) recommends breastfed infants receive vitamin D supplementation (400 to 800 IU/d) in support of optimal plasma 25‐hydroxy vitamin D (25(OH)D), defined as 75 nM. The objective of this study was to establish a dosage of vitamin D that would support optimal status in 97% of young infants. Healthy term born infants from Montreal (32 girls, 46 boys) were randomized to 400, 800 or 1200 IU vitamin D3 daily from age 4 wk and plasma 25(OH)D (RIA, Diasorin Inc.) measured at baseline, 4, 8 and 20 wk (NCT00381914; clinicaltrials.gov). Blinded treatments were re‐coded. Repeated measures ANOVA (by ITT) accounting for within‐subject serial correlations demonstrated season of birth, weight, time, treatment and treatment‐time interaction as significant (p<0.01) predictors of 25(OH)D. Table 1 shows estimated means by time and treatment. Mean 25(OH)D concentrations were higher over time (p<0.01) in dose regimen A vs. other treatments. Using 25(OH)D categories, overall 32% were above 75 nM after the 20 wk intervention. These results suggest that daily dosages of vitamin D from 400 to 1200 IU support a mean 25(OH)D concentration above that associated with deficiency, but the majority do not reach optimal status by 20 wk of supplementation. Estimated mean 25(OH)D ± SE (nM) [% reaching 75 nM]. Time points Treatments A (n=25) B (n=25) C (n=28) Baseline 47.8 ± 3.7 [0.0] 42.8 ± 3.7 [0.0] 41.7 ± 3.8 [4.0] 4 wk 63.4 ± 2.8† [28.6] 44.3 ± 2.8‡ [0.0] 40.8 ± 2.8‡ [0.0] 8 wk 57.6 ± 2.4 [5.3] 47.1 ± 2.3‡ [0.0] 51.7 ± 2.2 [8.7] 20 wk 84.0 ± 5.3† [38.9] 76.7 ± 5.3† [23.5] 77.0 ± 4.6† [33.3] p<0.05 vs treatment‐specific baseline, p<0.05 vs treatment A at same time. Grant Funding Source: Canadian Institutes of Health Research