Vitamin E Clinical Evidence

Carcinogenesis
Ju J, et al. Cancer preventive activities of tocopherols and tocotrienols. 2009 Sep 11. 

Topic: 
Can vitamin E tocopherols and tocotrienols help prevent cancer?

Background:

Vitamin E is not one compound but eight: four tocopherol isomers and four tocotrienol isomers. While some population studies have suggested that vitamin E protects against cancer formation, many large-scale studies in which people received supplements of alpha-tocopherol have not demonstrated an anti-cancer effect. Why?

Study Type:

Review paper

Results:

The authors of this paper:

  • Propose that a possible lack of demonstrable cancer- preventative effects of vitamin E could be because high doses of alpha-tocopherol deplete levels of gamma-tocopherol. That’s problematic, because gamma-tocopherol is strongly anti-inflammatory, and may be the most effective form of vitamin E in cancer prevention.
  • Discuss the biochemical properties of tocopherols, results of possible cancer preventive effects in humans and animals and possible mechanisms of action.

Conclusion:

“We propose that a gamma-tocopherol-rich mixture of tocopherols is a very promising cancer preventive agent and warrants extensive future research.” 

Journal of the National Cancer Institute 
Weinstein SJ, et al. Serum alpha-tocopherol and gamma-tocopherol in relation to prostate cancer risk in a prospective study. 2005 Mar 2;97(5):396-9. 

Topic: 
What is the relationship between blood levels of alpha- and gamma- tocopherol and prostate risk?

Background:

The Alpha-Tocopherol, Beta-Carotene Cancer Prevention (ATBC) study showed that people who took daily alpha-tocopherol supplements experienced a 32% reduction in prostate cancer incidence. Does gamma-tocopherol have a similar protective effect?

Study Type:

Human clinical observation trial

Study Design:

Randomized, controlled: Incident prostate cancer case patients from the ATBC trial were matched with control subjects from the study cohort of over 29,000 participants.

Subjects:

100 prostate cancer patients, 200 cancer-free controls

Results:

The association between high blood levels of tocopherols and low prostate cancer risk was stronger in the subjects who took alpha- tocopherol supplements than in those who did not. Importantly, participants with higher circulating concentrations of alpha and gamma-tocopherols had similarly lower prostate cancer risk. 

Vitamin E (mixed tocopherols) Mechanism of Action

Gamma tocopherol, a form of Vitamin E, inhibits the formation of tumors through its anti-inflammatory properties. Cell studies have found that prostate cancer cells treated with gamma tocopherol were less likely to progress to the S phase of the cell cycle (a phase associated with DNA synthesis, which occurs just before the cancer cells divides). Moreover, prostate cancer cells treated with gamma tocopherol contained decreased levels of substances associated with the formation of tumors and the progression of cancer cells from stage G1 of the cell cycle to stage S. All these actions together suggest that gamma tocopherol inhibits the progression of cancer cells through the cell cycle.