Spotlight on vitamin E

Areas of Active Research

Over the past few years, there have been some exciting research findings on vitamin E. For instance, vitamin E is one of the antioxidants found to reduce the risk of disease progression and vision loss in high risk patients with age related macular degeneration. A number of observational studies suggest that consuming foods high in vitamin E might reduce the risk of developing Parkinson's disease or Alzheimer's.

More Than "Just" an Antioxidant

Vitamin E was discovered eighty years ago to be essential for the reproductive health of certain animals. Today, this vitamin is established as the most important antioxidant in our cell membranes and as a key player in protecting cells against free radical damage. There is also growing recognition that vitamin E is more than just an antioxidant. For example, it helps regulate the ability of cells to communicate with one another, and the activity of genes. It also influences our natural defense system, and has been shown to help restore the age-related decline in immune function.

Vitamin E: The Extended Vitamin Family

Mention vitamin E and most people think only of alpha-tocopherol. But the term " vitamin E" refers to a family of eight related antioxidant compounds widely distributed in plants (see inset). Alpha tocopherol has long been considered the family "leader", not only because it's a potent antioxidant, but because the body actually prefers it. Our blood and tissues contain significantly more alpha-tocopherol than gamma-tocopherol, for example. This is because a special protein in the liver recognizes alpha-tocopherol and selectively transfers more of it into the blood stream.

The Role of Lesser-Known Family Members

Despite this "preferential" treatment of alpha tocopherol, small amounts of other members do get into tissues where they are believed to have important health functions. In experimental studies, gamma tocopherol neutralizes some kinds of free radicals better than alpha, and also helps to conserve alpha. When applied on the skin, a mixture of tocopherols and tocotrienols provides longer protection than alpha tocopherol alone. But do these experimental findings reflect what happens inside the body, since we selectively choose alpha tocopherol over other family members? There's some evidence from human studies that the gamma form, at least, may play a protective role. One study found a strong protective link between higher blood levels of gamma tocopherol and better prostate health.

Future Research Directions

There is much to unravel regarding the potential contributions of vitamin E family members, as well as how much of them we are getting in our diet and what amount we should aim to consume. However from what we know now, it appears that while alpha tocopherol is the quarterback and star player of the team, it is not the whole team.

References

1. Brigelius-Flohe et al. Review: The European perspective on vitamin E: current knowledge and future research. AJCN 76:703-16, 2002
2. Christian S et al. Gamma tocopherol traps mutagenic electrophiles such as NO(X) and complements alpha tocopherol: physiological implications. PNAS 94:3217-22, 1997.
3. Engelhart MJ et al. Dietary intake of antioxidants and risk of Alzheimer disease. JAMA 287:3223-9, 2002.
4. Helzlsouer KJ et al. Association between alpha tocopherol, gamma-tocopherol, selenium and subsequent prostate cancer. J Natl Cancer Inst 92:2018-33, 2000.
5. Jiang Q et al. Gamma tocopherol supplementation inhibits protein nitration and ascorbate oxidation in rats with inflammation. Free Rad Biol Med 33:1534-42, 2002.
6. Zhang SM et al. Intakes of vitamin E and C, carotenoids, vitamin supplements, and PD risk. Neurology 59:1161-69, 2002