Flawed Study Seeks To Discredit Value Of Vitamin D In Preventing Prostate Cancer
On May 27, 2008, the Journal of the National Cancer Institute published a population-based analysis of the relationship between prostate cancer risk and serum 25-hydroxy vitamin D level in aging men.1
The results of this population-based study prompted the study authors to conclude that vitamin D does not reduce the risk of prostate cancer, and furthermore that higher circulating levels of 25-hydroxy vitamin D may be associated with an increased risk of more aggressive forms of prostate cancer.
Given the study’s surprising results, and the fact that other studies show that high levels of the active form of vitamin D have strong anti-cancer effects as well as inhibit the growth and invasion of prostate cancer cells,234 Life Extension’s scientific team conducted a detailed review of the study.
In this rebuttal, Life Extension meticulously dissects the various flaws in this government-funded study. For those who don’t want to read these technical details, the following is all vitamin D supplement users need to know:
Only 6.3% of the men diagnosed with prostate cancer in the study were ingesting at least 1,000 IU of dietary vitamin D daily (only 49 men out of the total of 781 men diagnosed with prostate cancer in the trial were ingesting at least 1,000 IU of vitamin D in the diet every day). Furthermore, the vitamin D blood levels of the study subjects were so low over-all that it is likely most of these study subjects took no supplemental vitamin D whatsoever.
Therefore, the results of this study have no relevance to men who are taking the recommended amounts of vitamin D to achieve optimal blood ranges.
The headline hungry media reported on this study as if it showed there to be no value in taking vitamin D supplements, when in fact it appears that the study subjects were not optimizing vitamin D supplementation.
As you will read, there are numerous other flaws that rendered the findings from this study utterly meaningless. Due to its publication in a government-funded journal, this study will dissuade many aging American men from taking vitamin D, which is great news for pharmaceutical companies who sell drugs to treat the multiple degenerative diseases caused by a vitamin D deficiency.
Limitations in study design – multiple sources of error
When scientists interpret scientific studies, bias is an important, often overlooked source of error. In this context, bias refers to any factor in the study that may create the potential for error.
This means that there is a high level of uncertainty with any attempt to associate a single, isolated serum 25-hydroxy vitamin D level that varies by at least 20% by time of year with prostate cancer risk over time.
Other prospective clinical studies show benefit
Three other prospective clinical studies have shown benefit with higher levels of circulating serum 25-hydroxy vitamin D and prostate cancer risk:
The current study suggesting an increase in prostate cancer risk with serum 25-hydroxy vitamin D is flawed.
From seasonal variability in vitamin D levels to detection bias associated with higher PSA levels, the study design is plagued with bias.
In addition, the inadequate over-all serum 25-hydroxy vitamin D levels achieved in the trial (approximately 22.4 ng/ml) are far below optimal levels of around 50-60 ng/mL and renders any meaningful interpretation of the trial results impossible.
1.Ahn J, Peters U, Albanes D, Purdue MP, Abnet CC, Chatterjee N, Horst RL, Hollis BW, Huang WY, Shikany JM, Hayes RB; For the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial Project Team. Serum Vitamin D Concentration and Prostate Cancer Risk: A Nested Case-Control Study. J Natl Cancer Inst. 2008 May 27.
2.Skowronski RJ , Peehl DM , Feldman D . Vitamin D and prostate cancer: 1,25 dihydroxyvitamin D3 receptors and actions in human prostate cancer cell lines . Endocrinology . 1993 ; 132 ( 5 ): 1952 – 1960.
3.Peehl DM , Skowronski RJ , Leung GK , Wong ST , Stamey TA , Feldman D . Antiproliferative effects of 1,25-dihydroxyvitamin D3 on primary cultures of human prostatic cells . Cancer Res. 1994 ; 54 ( 3 ): 805 – 810.
4.Oades GM , Dredge K , Kirby RS , Colston KW . Vitamin D receptor dependent antitumour effects of 1,25-dihydroxyvitamin D3 and two synthetic analogues in three in vivo models of prostate cancer . BJU Int .2002 ; 90 ( 6 ): 607 – 616 .
5.Vieth R. Vitamin D supplementation, 25-hydroxyvitamin D concentrations, and safety. Am.J Clin Nutr. 1999 May;69(5):842-56.
6.Holick MF. The role of vitamin D for bone health and fracture prevention. Curr Osteoporos Rep. 2006 Sep;4(3):96-102.
7.Jacobs ET , Giuliano AR , Martinez ME , Hollis BW , Reid ME , Marshall JR . Plasma levels of 25-hydroxyvitamin D, 1,25-dihydroxyvitamin D and the risk of prostate cancer . J Steroid Biochem Mol Biol. 2004 ; 89 – 90 ( 1 – 5 ): 533 – 537.
8.Ahonen MH , Tenkanen L , Teppo L , Hakama M , Tuohimaa P . Prostate cancer risk and prediagnostic serum 25-hydroxyvitamin D levels (Finland) . Cancer Causes Control . 2000 ; 11 ( 9 ): 847 – 852 .
9.Nomura AM , Stemmermann GN , Lee J , et al . Serum vitamin D metabolite levels and the subsequent development of prostate cancer (Hawaii, United States) . Cancer Causes Control . 1998 ; 9 ( 4 ): 425 – 432 .