"What effects, then, can we expect from artificially raising the vitamin D levels of black Americans? Keep in mind that we are really talking about a hormone, not a vitamin. This hormone interacts with the chromosomes and may gradually shorten their telomeres if concentrations are too low or too high. Similarly, cancer risk increases if concentrations are too low or too high. Prostate cancer is least likely when vitamin D levels vary between 16 and 24 ng/mL -- a range of values below the current recommended minimum of 30 ng/mL."The reference for that highlighted text above was...
- Black-White Differences in Cancer Risk and the Vitamin D Hypothesis, Journal of the National Medical Association, December 2009
"Calcidiol* serum concentrations show a U-shaped risk of prostate cancer suggesting an optimal serum concentration of 40-60 nmol/L [16-24 ng/mL] for the lowest cancer risk."*Calcidiol, 25(OH)D, is vitamin D3 that has been hydroxylated by the liver. Serum calcidiol is an indicator of vitamin D status.
- Vitamin D and Aging, The Journal of Steroid Biochemistry and Molecular Biology, December 2009
It will be interesting to see what recommendations the IOM makes regarding vitamin D intake. They've been holding a series of meetings on it. (The IOM is the Institute of Medicine of the National Academies. They publish the DRIs/RDAs.)
Here are the current recommendations for vitamin D that are likely to go up: