Table 1. Comparison of serum 25(OH)D levels in 5,571 young children stratified by age, season or gender.

Group	N	Serum 25(OH)D (nmol/L)
		Median	Percentile (p25-p75)
Age
1 y a , b	3845	74.70	56.40–94.25
2 y a , c	1266	67.60	53.48–84.93
3 y b , c	460	61.00	52.30–76.75
Season
Spring d , e , f	1256	71.6	56.3–93.3
Summer d , g , h	907	74.4	58.7–93.3
Autumn e , g , i	1471	69.0	52.6–86.6
Winter f , h , i	1937	71.4	54.3–91.2
Gender
Boy j	2903	72.3	55.5–91.2
Girl j	2668	70.8	54.7–90.3

Values of serum 25(OH)D levels were compared using Mann–Whitney U test.

^a significant difference between children aged 1y and aged 2y (P<0.001).

^b Significant difference between children aged 1y and aged 3y (P<0.001).

^c Significant difference between children aged 2y and aged 3y (P<0.001).

^d No significant difference between spring and summer (P = 0.076).

^e Significant difference between spring and autumn (P<0.001).

^f No significant difference between spring and winter (P = 0.098).

^g Significant difference between summer and autumn (P<0.001).

^h Significant difference between summer and winter (P = 0.001).

ⁱ Significant difference between autumn and winter (P = 0.003).

^j No significant difference between boys and girls (P = 0.121).