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For very young children in this life stage group, virtually no data are available to link vitamin D nutriture directly to measures related to bone health outcomes. AHRQ-Ottawa examined the relationship between vitamin D and rickets in children 0 to 5 years of age but found no studies that evaluated BMC, BMD, or fractures in comparison with measures of vitamin D intake. Likewise, AHRQ-Tufts found no studies that update AHRQ-Ottawa.

AHRQ-Ottawa did consider serum 25OHD concentrations in the context of the onset of rickets in newborns through children 5 years of age and identified serum concentrations below 27.5 nmol/L as being consistently associated with rickets. However, many of the relevant studies were from developing countries where calcium intake is low; therefore, for these studies, the onset of rickets was associated with higher levels of 25OHD in serum, likely due to low calcium intakes. Specker et al. (1992) has concluded that serum concentrations of approximately 27 to 30 nmol/L places the infant at an increased risk for developing rickets, although the measure is not diagnostic of the disease.

Although the prevention of rickets can be a factor in establishing reference values, it is important to seek measures that are consistent with favorable bone health outcomes. Maximizing calcium absorption, especially for this life stage group, is therefore a reasonable parameter to take into account. Here, as with rickets, serum 25OHD measures are the only data available and there are no direct measures of vitamin D intake. Abrams et al. (2009) conducted calcium absorption studies in 251 children ranging in age from 4.9 to 16.7 years and found that children with serum 25OHD levels of 28 to 50 nmol/L had higher fractional calcium absorption than children with serum 25OHD levels at or greater than 50 nmol/L, suggesting again at the least that maximal calcium absorption is reached at 50 nmol/L. Fractional calcium absorption did not increase with serum 25OHD concentration levels above 50 nmol/L. The findings are consistent with the conclusions reached previously concerning serum 25OHD levels associated with maximum population coverage. Further, as rickets in populations that are not calcium deficient occurs at serum 25OHD levels below 30 nmol/L, it is reasonable to assume that 40 nmol/L is associated with an average requirement.

Serum 25OHD concentrations of 40 to 50 nmol/L would ideally coincide with bone health benefits such as positive effects on BMC and BMD. AHRQ-Ottawa found that there was fair evidence that circulating 25OHD levels are associated with a positive change in BMD and BMC in studies in older children and adolescents. The serum 25OHD concentrations varied from 30 to 83 nmol/L. A study conducted by Viljakainen et al. (2006) reported that vitamin D intakes of 200 and 400 IU/day in adolescent girls were associated with positive BMC measures at serum 25OHD levels



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