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Thursday, August 4, 2011

Vitamin D Review

[August 4, 2011]

A review paper by Barnett and Beer that appeared in Urol Clin North Am. 2011 Aug;38(3):333-42 discusses the current status of Vitamin D research. [PMID: 21798396]. According to that paper it seems clear that vitamin D is involved in prostate cancer biology and that there is an anticancer effect in animals but it is much less clear whether there is a significant beneficial effect of vitamin D supplementation in humans. Below we outline the main points:
  • geographic areas of low UV exposure have increased risk of prostate cancer
  • in test tube and animal studies vitamin D has shown an anti-cancer effect
  • because calcium tends to depress vitamin D it would be expected that if vitamin D were anti-cancer in humans then low calcium intake would correlate with lower risk of prostate cancer but of 12 recent studies 8 showed no relationship with calcium
  • out of 13 studies 9 showed no association between low vitamin D and increased risk of prostate cancer
  • some caveats are that the following may (or may not) be (a) it might be that the studies just cited did not have sufficient numbers of patients to detect a difference, (b) it might be that the effect of low vitamin D is to increase the risk of aggressive prostate cancer rather than increase the risk of prostate cancer
  • studies relating genetic variations in Vitamin D genes and prostate cancer progression have been inconclusive
  • multiple studies with calcitriol + chemo have resulted in lower PSA levels; however, a phase III trial was halted due to deaths in the treatment arm
  • it may be that vitamin D therapy only works in certain targeted subgroups
In conclusion:
"At present, there are no consistent data to support high dose vitamin D supplementation for the average patient with prostate cancer for the treatment or halting of cancer progression. In addition, there are no data to support therapeutic use of vitamin D and its analogs in treating prostate cancer. Additional studies are needed to determine if higher doses of vitamin D supplements could benefit selected populations (ie, the elderly or patients with cancer) even if they may not be beneficial for the general population."
and for the average prostate cancer patient
"a recommended minimum of 600 IU of vitamin D per day, with testing at baseline to determine if additional supplementation is needed for deficiency levels (< 20 ng/mL) is reasonable."

1 comment:

Charles (Chuck) Maack said...

The study claims the calcium depresses Vitamind D. Hummm. Read the following "different" study:

Vitamin D, Fortification and Subway
August 4, 2011

Last month Professor Rebecca Mason of the University of Sydney and her co-authors wrote an excellent review of vitamin D.

Mason RS, Sequeira VB, Gordon-Thomson C. Vitamin D: the light side of sunshine. Eur J Clin Nutr. 2011 Jul 6. doi: 10.1038/ejcn.2011.105. [Epub ahead of print]

With two references, she confirmed what I always thought likely: higher calcium intake increases vitamin D levels. It makes sense, as less vitamin D is used up for absorbing calcium if calcium intake is high enough to trigger only passive calcium absorption.

I also liked her reiteration of vitamin A’s ability to interfere with the function of vitamin D, something I have written about in detail. I continue to think cod liver oil is confounding many vitamin D studies.

In several places, Professor Mason questions whether ethical concerns will mean that randomized controlled trials will never be done. After all, do you want to be randomized to the 600 IU/day control group? Not me.

I also liked her brief discussion of a wonderful paper that I wrote about last year on the study of 675 fresh cadavers. The authors compared bone biopsies and vitamin D levels of the cadavers to conclude that vitamin D levels of at least 35 ng/ml are needed for healthy bones, a study the recent FNB must have missed.

My only criticism is her failure to realize that food fortification is essential for large subgroups of the globe’s population. For example, African Americans are unlikely to seek sun exposure or take vitamin D supplements, proven by the fact that so many black women of childbearing age have vitamin D levels less than 10 ng/ml.

It appears as though some food companies are picking this up. Yesterday, Subway (the world’s largest food chain in terms of restaurant units) announced they will begin adding about 100 IU of vitamin D to the bread they use to make their subs.

Subway's 'Healthy' New Bread Will Include Vitamin D, Calcium

Although 100 IU is a menial amount of vitamin D, every little bit helps. And with Subway’s large and global influence, they might even help spread a little awareness.

-John J. Cannell, M.D.