Vitamin D status of schoolchildren in Northern Algeria, seasonal variations and determinants of vitamin D deficiency

There are no published data on the vitamin D status of children living in North Africa. In 435 healthy Algerian children 5-15 years old, we found that vitamin D insufficiency (serum 25-hydroxyvitamin D (25OHD) < 50 nmol/L) was frequent, especially in winter. Low vitamin D status was associated with increased parathyroid hormone (PTH) and leg deformation As there are no published data on the vitamin D status of children living in North Africa, we evaluated the 25OHD concentration of healthy Algerian children at the end of summer and at the end of winter. As secondary objectives, we studied the various determinants of vitamin D status and the PTH-25OHD relationship in these subjects. Four hundred thirty-five children 5-15 years old were examined and had a blood sample in September 2010. Of them, 408 were sampled again in March 2011. Median 25OHD concentration in the whole group was 71.4 nmol/L in September and 52.9 nmol/L in March. In September, 58.4, 29.9, and 8.1 % had a 25OHD concentration below 75, 50, and 30 nmol/L respectively. In March, these percentages increased to 65.2, 41.4, and 17.4 % for the 75, 50, and 30 nmol/L threshold, respectively. In multivariate analysis, older age, darker skin phototype, low daily vitamin D and calcium intake, poor socioeconomic status, and short daily sun exposure remained significantly associated with a 25OHD < 50 nmol/L at both visits. In 72 (16.6 %) children, genu varum/valgum was present. Compared to the 363 children without leg deformation, they presented more frequently with the risk factors of vitamin D insufficiency. They also had lower 25OHD concentrations and higher PTH and tALP. Serum PTH and 25OHD concentrations were negatively and significantly correlated (r = -0.43; p < 0.001) without a 25OHD threshold above which PTH does not decrease anymore. Despite a sunny environment, vitamin D insufficiency is frequent in healthy Algerian children.