Fig. 3.

Box-and-whisker plots† showing the difference in serum 25-hydroxyvitamin D (s-25(OH)D) concentration (nmol/l) between those taking vitamin D supplements (fish-liver oil or other vitamin D supplements) and those not taking vitamin D supplements among 7-year-old Icelandic girls and boys (n 120), Reykjavík, 2006. The median concentration of s-25(OH)D was not significantly different between the two groups according to the independent t test (P = 0·009). Median vitamin D intake for the group taking vitamin D supplements was 8·8 μg/d (equivalent to about 4·5 ml of fish-liver oil daily) and 2·0 μg/d for the group that did not take vitamin D supplements. There was a significant difference in vitamin D intake between the group taking vitamin D supplements and the one that did not (P < 0·001), based on the Mann–Whitney U test. †The line within the box represents the median value; the bottom and top edges of the box represent the 25th percentile and 75th percentile (i.e. the interquartile range), respectively; the bottom and top whiskers represent the minimum and maximum values, respectively; and the circles represent outliers. Optimal serum vitamin D status is ≥50 nmol/l (———)