Sunday, June 27, 2010

How the vitamin D RDI was set.

I'm unsure if I covered this specific information in my book...... however it is important enough to repeat even if I did. The first blood measurement of vitamin D, which is the chemical 25-hydroxycholecalciferol (25(OH)D3, was undertaken in 1971.

They studied 40 "healthy" volunteers of mean age of 30 years old. The volunteers didn't have any clear clinical signs of vitamin D deficiency. That is they didn't have osteomalacia which is like osteoporosis but occurs in younger people. It was determined that the 40 volunteers had a (25(OH)D3, level of  68 nmol, and their dietary intake was 318 IU per day. Thus the RDI of 400 IU for an adult was set. It was set higher than 318 IU most likely to make sure that the population who were poor vitamin D absorbers would still obtain a blood level of 68 nmol. On the other had it could have also been set at 400 IU to make sure that people got 318 IU, that is if people aimed to get 318, they might say only get 250 IU, where as aiming for 400 IU and obtaining 250 IU would be acceptable.


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