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Introduction: There is evidence that 25-hydroxyvitamin D levels are lower in overweight and obese youth. This study examined the relationship between weight status and 25-hydroxyvitamin D, while controlling for confounders, in Canadian youth. Methods: Plasma 25-hydroxyvitamin D from subjects aged 6 to 17 years from the Canadian Health Measures Survey cycles 1 (2007 to 2009) and 2 (2009 to 2011) was used. Sex-specific multiple linear regression and logistic regressions examined the relationship of overweight and obesity (body mass index = 85th percentile) with 25-hydroxyvitamin D levels and the odds of 25-hydroxyvitamin D <40 nmol/L and <50 nmol/L. Results: The prevalence of risk of vitamin D deficiency (25-hydroxyvitamin D < 30 nmol/L) was 6% (95% confidence interval [CI] 3.26% to 10.12%). Vitamin D inadequacy, estimated by levels <40 nmol/L, was 15% (95% CI 10.34% to 20.39%; 19% [95% CI 13.1 to 25.6] for teenagers). Seventy per cent (95% CI 63.59 to 75.17) had levels >50 nmol/L, consistent with achieving the Recommended Dietary Allowance. In adjusted analyses, overweight/obesity (1/3 of subjects) was independently associated with lower 25-hydroxyvitamin D for both sexes after adjustment for age, race, income, season, vitamin D supplementation and daily milk consumption. For 25-hydroxyvitamin D <40 nmol/L, the overweight/obese odds ratio for males was 2.63 (95% CI 1.34 to 5.18). For 25-hydroxyvitamin D <50 nmol/L, overweight/obese odds ratios were 2.19 (95% CI 1.46 to 3.28) for males and 1.39 (95% CI 1.05 to 1.84) for females. Conclusions: This study confirms the inverse association between adiposity and serum concentrations of 25-hydroxyvitamin D in Canadian youth and the independent association of overweight/obesity to 25-hydroxyvitamin D level and vitamin D status after adjustment for other factors. [ABSTRACT FROM AUTHOR]

Background: Vitamin D supplementation is recommended for breastfed infants. Maternal supplementation beginning in gestation is a potential alternative, but its efficacy in maintaining infant 25-hydroxyvitamin D [25(OH)D] concentration after birth is unknown. Objectives: We determined the effect of 3 doses of maternal vitamin D supplementation beginning in gestation and continued in lactation on infant serum 25(OH)D and compared the prevalence of infant serum 25(OH)D cutoffs (>30, >40, >50, and >75 nmol/L) by dose at 8 wk of age. Design: Pregnant women (n = 226) were randomly allocated to receive 10, 25, or 50 µg vitamin D3/d from 13 to 24 wk of gestation until 8 wk postpartum, with no infant supplementation. Mother and infant blood was collected at 8 wk postpartum. Results: At 8 wk postpartum, mean [nmol/L (95% CI)] infant 25(OH)D at 8 wk was higher in the 50-µg/d [75 (67, 83)] than in the 25-µg/d [52 (45, 58)] or 10-µg/d [45 (38, 52)] vitamin D groups (P < 0.05). Fewer infants born to mothers in the 50-µg/d group had a 25(OH)D concentration,30 nmol/L (indicative of deficiency) than infants in the 25- and 10-µg/d groups, respectively (2% compared with 16% and 43%; P< 0.05). Fewer than 15% of infants in the 10-or 25-µg/d groups achieved a 25(OH)D concentration .75 nmol/L compared with 44% in the 50-µg/d group (P < 0.05). Almost all infants (w98%, n = 44) born to mothers in the 50-µg/d group achieved a 25(OH)D concentration .30 nmol/L. At 8 wk postpartum, mean maternal 25(OH)D concentration was higher in the 50-µg/d [88 (84, 91)] than in the 25-µg/d [78 (74, 81)] or 10-µg/d [69 (66, 73)] groups (P< 0.05). Conclusions: Maternal supplementation beginning in gestation with 50 µg vitamin D3/d protects 98% of unsupplemented breastfed infants against 25(OH)D deficiency (<30 nmol/L) to at least 8 wk, whereas 10 or 25 µg vitamin D/d protects only 57% and 84% of infants, respectively. This trial was registered at clinicaltrials.gov as NCT01112891. [ABSTRACT FROM AUTHOR]