medwireNews: Higher doses of vitamin D3 than currently recommended may be needed to achieve vitamin D sufficiency in schoolchildren living at northern latitudes, show the results of a randomised trial.

However, the researchers stress that all three supplemental doses used – 600, 1000 or 2000 IU/day for 6 months – prevented severe vitamin D deficiency in all but a few children. The US Institute of Medicine currently advises a 600 IU/day dose.

The 604 children in the Daily D Health Study were aged an average of 11.7 years and had average baseline serum 25-hydroxyvitamin D (25[OH]D) levels of 22 ng/mL, with levels being insufficient (<30 ng/mL) in 88.6% and severely deficient (<12 ng/mL) in 5.5%.

The children started taking their supplements between October and December, and were followed up 3 months later, by which time average 25(OH)D levels had risen to 25.6 and 26.6 ng/mL in the 600 and 1000 IU/day groups, respectively, and to 33.1 ng/mL in the 2000 IU/day group.

Similar levels were recorded at the 6-month follow-up, at which point severe vitamin D deficiency was “virtually eliminated” in all three groups. Although average 25(OH)D levels were comparable between the 1000 and 600 IU/day dose groups, levels of deficiency (12–19 ng/mL) were lower with the higher dose, at 15.0% versus 22.9%.

The level was lower still among children taking the 2000 IU/day dose, at just 4.9%, and around 60% of this group achieved sufficient levels of 25(OH)D, compared with 35.8% and 26.6% of the 1000 and 600 ng/mL groups, respectively.

“Notably, these benefits of supplementation occurred over the winter months in northeastern U.S. when serum 25(OH)D tends to fall”, write Jennifer Sacheck (Tufts University, Boston, Massachusetts, USA) and study co-authors in The Journal of Clinical Endocrinology & Metabolism.

They note that adherence to the supplementation was high overall, with children taking a median of approximately 90% of pills, and did not differ significantly between the dose groups.

There was some variation across subgroups, which the researchers say warrants further study. They found that Black children had a significantly larger response to the highest supplementation dose than children of other racial groups. Although these children had some of the lowest starting 25(OH)D levels, so did Asian children, who did not have such a marked response to supplementation.

Conversely, obese children had the poorest response to the highest supplementation dose, which the researchers suggest may be “due to differences in metabolism or more sequestration of vitamin D in adipose tissue in response to higher doses in obese children”.

All children were reassessed 6 months after finishing the trial and although their 25(OH)D levels fell to around 25 ng/mL in all three groups over this period they did not return to baseline, which the team describes as a “striking” finding.

By Eleanor McDermid

J Clin Endocrinol Metab 2017; Advance online publication

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