Vitamin A: new data imply potential for preventive effects

Now after you have read this, we do not think you should be rushing out to fill your medicine cabinet with vitamin A. We need more research to validate the results of this study, but …

Vitamin A — also known as retinol — has been studied before for its potential as a chemopreventive agent for prostate cancer. In the past, data from studies on the association between circulating retinol concentrations and the risk of prostate cancer have varied, but we do know that retinol is important in the regulation of cell growth and differentiation.

Using data from > 1,500 men who participated in the Prostate, Lung, Colorectal, and Ovarian Cancer (PLCO) screening trial, Schenk et al. examined whether serum concentrations of retinol were associated with overall risk for prostate cancer and risk for aggressive disease (stage III or IV or Gleason > 7).

Now this is a retrospective analysis of data from the PLCO trial and it used what is known as a “nested case-control” methodology, in which patients with prostate cancer were compared to men who were very like the patients but did not have prostate cancer. There are all sorts of difficulties assessing the results of nested case control studies because of the assumptions that have to be made in the design of such trials.

So — with that provision — the results published by Schenk and her colleagues are as follows:

  • The trial cohort included 692 men with prostate cancer and 844 matched controls.
  • 269 of the patients met criteria for having aggressive disease.
  • Serum retinol concentrations were not significantly associated with overall prostate cancer risk.
  • Men with the highest levels of serum retinol were 42 percent less likely to have aggressive prostate cancer than men with the lowest levels of serum retinol.

The authors state that their results “suggest that higher circulating concentrations of retinol are associated with a decreased risk of aggressive prostate cancer.” However they also emphasize the need for additional research “to better understand the significance of elevations in serum retinol concentrations and the possible biological mechanisms through which retinol affects prostate cancer.”

A report on this study in Cancer Monthly includes additional commentary from Dr. Schenk, as follows:

  • Eating vitamin A-rich foods or taking supplements won’t do much to increase vitamin A levels in the blood and so may not affect  risk for prostate cancer.
  • Retinol concentrations are affected by factors such as body mass index, physical activity, and the amount of fat in the diet.

In other words, even if the study results are accurate, and men with the highest levels of vitamin A in their blood are at reduced risk for prostate cancer, changing your diet or taking supplements won’t necessarily raise vitamin A levels in the blood for individual patients in ways that are safe and that would be sure to have the desired impact on prostate cancer risk.

We are a little puzzled by the fact that the number of prostate cancer patients in this study reported in the Cancer Monthly article (n = 803) is very different from the number reported by Schenk et al. in their abstract (n = 692) but there may be a good explanation for this based on eligibility criteria.

2 Responses

  1. About 10 years ago, while the ophthalmic community and NIH were demonstrating that vitamin therapy that included large doses of vitamin A (as beta-carotene) reduced the risk of vision loss from macular degeneration, studies similar to this one (serum levels of retinol on prostate cancer) on smokers appeared to show a reduced lung cancer risk with higher serum levels of vitamin A. Studies were done to try to protect the smokers from lung cancer by supplementing diets with vitamin A. The lung cancer rate went UP, not DOWN. The eye community had to come up with a “smokers formula” and recommend that smokers should not take any vitamin A supplements. These were good double blind studies. Similar studies need to be done in the setting of prostate cancer before any recommendation for supplementation can be made. I think the Sitemaster has hit the nail on the head.

  2. I am a little baffled by the commentary by Dr. Schenk stating that taking supplemental vitamin A won’t do much to increase vitamin A levels in the blood. That is simply not true. The pharmacokinetics of vitamin A have it’s plasma concentrations peaking between 3 and 5 hours after ingestion. To me, his comment reaches beyond what the science of the study said to speculation, at best. Additionally, to comment upon the smokers/lung cancer/beta carotene risk, I will say that there are many reasons this might have been the case, the most likely, in my mind, being a concomitant vitamin D deficiency. Google “Chris Masterjohn and vitamin A toxicity” to get some good information on this.

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