[Vitamin D status in 6- to 10-year-old children: a French multicenter study in 326 children]

To assess the vitamin D status of children aged 6-10years in the French general population for whom no guidelines have yet been defined due to insufficient data.

The study was conducted during two winters with very different sunshine levels: 5 March to 17 April 2012 and 8 January to 16 April 2013 in 20 then 22 centers. Three hundred children (60 children for each year of age) attending an ambulatory care unit or outpatient department for a reason unrelated to vitamin D status were included at the end of winter in 20 hospital centers (ten centers in the northern half of France above latitude 46-47°N/Lille: 50°N and ten centers in the southern half of France below latitude 46-47°N/Marseille: 43°N). Centralized 25 hydroxyvitamin D (25(OH)D), alkaline phosphatase (ALP), and parathormone (PTH) assays were performed on leftover blood samples. The currently accepted normal range for 25(OH)D was used to define the following categories: ≤25nmol/L: severe vitamin D deficiency, 25nmol/L100nmol/L: high vitamin D status. A standardized questionnaire was used to collect the child's characteristics, use of a vitamin D supplement, and milk and dairy product intake. The cumulative number of hours of sunshine over the 90days prior to inclusion in each center was obtained from the Météo-France weather bureau.

25(OH)D assays were performed in 326 children; more than 95% of children received milk and dairy products and 38% had received a vitamin D supplement since starting the school year: 3.1% of children in the overall population presented severe vitamin D deficiency, 34.4% presented vitamin D deficiency, 53.1% had a sufficient vitamin D status, and 9.5% had a 25(OH)D concentration >100nmol/L with no impact on serum calcium and urinary calcium. Children living in the north of France generally had lower 25(OH)D levels than children living in the south of France. In the non-supplemented population (n=188), 5.3% of children presented severe vitamin D deficiency, 45.2% presented vitamin D deficiency and 48.4% had sufficient 25(OH)D levels. The percentage of children with severe vitamin D deficiency or vitamin D deficiency was twofold higher during the winter with poor sunshine compared to the sunnier winter with a less marked north/south difference. No case of severe vitamin D deficiency was observed in the supplemented population (n=119); 10-15% of children presented vitamin D deficiency and 22.7% had a 25(OH)D concentration >100nmol/L, while remaining within the acceptable range. Two cases of hypervitaminosis without hypercalcemia were identified: one after an unknown loading dose with a calcium/creatinine ratio in the normal range (0.8); for the second one, no additional information could be obtained. Vitamin D supplementation considerably reduced the north/south difference and the Winter1/Winter2 difference. A child not receiving a vitamin D supplement had a ninefold higher risk of vitamin D deficiency at the end of winter than a child receiving a vitamin D supplement (OR=8.8; 95%CI, 4.6-16.8).

At least one-third of children aged 6-10years presented deficient 25(OH)D levels. None of the children receiving a vitamin D supplement presented severe vitamin D deficiency, only a small number of children presented vitamin D deficiency (n=16 (13.4%)), and no signs of overload were observed, while one half of non-supplemented children (n=95 (50.5%)) presented at least vitamin D deficiency at the end of winter. These results support the need for vitamin D supplementation during winter in children aged 6-10years.