Puzzling vitamin D results
==========================

* Trevor G. Marshall

I am puzzled by the seasonal mean values for 1,25- dihydroxy vitamin D [1,25-(OH)2D] published in Table 2 of the article by Diana Rucker and colleagues.1 They are about twice as high as those from a similar study done in Denmark,2 which showed a mean of 29 pg/ml (75.4 pmol/L). 

Two of the seasonal mean values (168.1, 148.9) are above the normal range quoted for the assay (45–145). This assay range seems to be correct, but the study data seem to be high. 

I am particularly concerned that this study did not place much greater emphasis on the values of the active hormone 1,25-(OH)2D than on the intermediate metabolite 25-hydroxy vitamin D [25(OH)D]. This is especially important in elderly populations, as extra- renal hydroxylase activity in inflammatory macrophages has been shown to generate a normal 1,25-(OH)2D value from depressed levels of circulating 25(OH)D. 

**Trevor G. Marshall** Research Director Yarc Inc. Thousand Oaks, Calif.

## References

1.  1. Rucker D, Allan JA, Fick GH, Hanley DA. Vitamin D insufficiency in a population of healthy western Canadians. CMAJ 2002;166(12):1517-24.
    
    [Abstract/FREE Full Text](http://www.cmaj.ca/lookup/ijlink/YTozOntzOjQ6InBhdGgiO3M6MTQ6Ii9sb29rdXAvaWpsaW5rIjtzOjU6InF1ZXJ5IjthOjQ6e3M6ODoibGlua1R5cGUiO3M6NDoiQUJTVCI7czoxMToiam91cm5hbENvZGUiO3M6NDoiY21haiI7czo1OiJyZXNpZCI7czoxMToiMTY2LzEyLzE1MTciO3M6NDoiYXRvbSI7czoyMjoiL2NtYWovMTY3LzgvODQ5LjEuYXRvbSI7fXM6ODoiZnJhZ21lbnQiO3M6MDoiIjt9) 

2.  2. Brot C, Jorgensen NR, Sorensen OH. The influence of smoking on vitamin D status and calcium metabolism. Eur J Clin Nutr 1999;53(12): 920-6. 
    
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