Vitamin D metabolite levels in normal children

Vitamin D metabolite levels were measured in 174 normal children throughout the year. 25-hydroxyvitamin D3 (25(OH)D3) and 24,25-dihydroxyvitamin D3 (24,25(OH)2D3) levels showed a seasonal variation; both levels were higher in summer than in winter (p less than 0.001 for both). There was a fall in the 1,25-dihydroxyvitamin D (1,25(OH)2D) level in August and September (p less than 0.001), which coincided with a rise in mean 25(OH)D3 and 24,25(OH)2D3 levels. An inverse correlation was seen between 1,25(OH)2D and 24,25(OH)2D3 levels (r = -0.233; p less than 0.01). 25(OH)D3 levels increased with age only for winter values (less than 3 years, 11.70 +/- 3.98 ng/ml; 3-11 years, 18.38 +/- 1.65 ng/ml; greater than 11 years, 23.60 +/- 4.60 ng/ml) while 1,25(OH)2D and 24,25(OH)2D3 levels did not show an age-related difference. Intake of multivitamins had an interesting effect on 25(OH)D3 and 24,25(OH)2D3 levels in the winter but not in the summer; the endogenous metabolite levels were lower in the vitamin supplemented children [25(OH)D3: 23.05 +/- 7.35 versus 15.77 +/- 5.51 ng/ml, p less than 0.001; 24,25(OH)2D3: 2.30 +/- 1.11 versus 1.66 +/- 0.88 ng/ml, p less than 0.05]. Children studied in the winter who were not receiving supplemental vitamins were older than those who did receive the vitamins (7.26 +/- 2.64 versus 5.42 +/- 3.17 years; p less than 0.01). Sixteen of the children had both winter and summer measurements. Their 25(OH)D3 and 24,25(OH)2D3 levels showed the same seasonal variation as the overall group data, while their 1,25(OH)2D levels showed no consistent pattern.(ABSTRACT TRUNCATED AT 250 WORDS)