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Vitamin E Gets Mixed Reviews Because It's a
Double-Edged Sword
March 3, 2006 Vitamin E good or bad has been
a hot topic in medicine for the last couple of years. New research at
Ohio State University, looking at how two forms of vitamin E act inside
animal cells, has concluded this powerful antioxidant, popular with
senior citizens, is "truly a
double-edged sword."
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In the past couple of decades, a slough of studies
has looked at the benefits of vitamin E and other antioxidants. While a
considerable amount of this research touts the advantages of consuming
antioxidants, some of the studies have found that in certain cases,
antioxidants, including
vitamin E, may actually increase the potential for developing heart
disease, cancer and a host of other health problems.
This study provides clues as to why this could
happen, say
Jiyan Ma, an assistant professor of
molecular and cellular biochemistry, and his colleague David
Cornwell, an emeritus professor of molecular and cellular biochemistry,
both at Ohio State.
The two men led a study that compared how the two
most common forms of vitamin E one is found primarily in plants like
corn and soybeans, while the other is found in olive oil, almonds,
sunflower seeds and mustard greens affect the health of animal cells.
The main difference between the two forms is a slight variation in their
chemical structures.
In laboratory experiments, the kind of vitamin E
found in corn and soybean oil, gamma-tocopherol, ultimately destroyed
animal cells. But the other form of vitamin E, alpha-tocopherol, did
not. (Tocopherol is the scientific name for vitamin E.)
In the United States we tend to eat a diet rich in
corn and soybean oil, so we consume much greater amounts of gamma-tocopherol
than alpha-tocopherol, Cornwell said. But most of the vitamin E
coursing through out veins is alpha-tocopherol the body selects for
this version. We want to know why that is, and whether the selection of
the alpha-tocopherol confers an evolutionary benefit in animal cells.
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While the study
doesn't get into the possible effects on health, the researchers
raise the point that there is still a great deal that isn't
known about how antioxidants act in the body.
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Cornwell and Ma explain their findings in this
week's Early Edition of the
Proceedings of the National Academy of Sciences. They conducted the
study with several colleagues from the departments of molecular and
cellular biochemistry and
chemistry at Ohio State.
The researchers conducted laboratory experiments on
cells taken from the brains of mice. They treated some of the cells with
metabolic end products, called quinones, of alpha- and gamma-tocopherol.
When the body breaks down vitamin E, these end
products are what enter and act on our cells. However, Ma said that our
bodies get rid of most gamma-tocopherol before it ever has a chance to
reach its quinone stage.
Still, some nutritional supplement companies make
and sell gamma-tocopherol supplements, promoting this version of vitamin
E as a good antioxidant source. In theory, taking a vitamin supplement
a concentrated form of the vitamin - increases the amount of that
substance in the body.
Using laboratory techniques that allowed them to
detect the activity of the quinones inside the cells, the researchers
found that the gamma-tocopherol quinone formed a compound which
destroyed that cell. It did so by preventing proper protein folding in
the cells, which causes a cellular response that is involved in a
variety of human diseases, including diabetes and Parkinson's disease.
However, the alpha-tocopherol quinone did not kill
cells, nor did it interfere with protein folding. The researchers
repeated their experiments on kidney cells cultured from monkeys and on
skin cells cultured from mice and found similar results.
We think that gamma-tocopherol may have this kind
of damaging effect on nearly every type of cell in the body, Ma said.
While the study doesn't get into the possible
effects on health, the researchers raise the point that there is still a
great deal that isn't known about how antioxidants act in the body. In
order to get to that point, scientists must study how antioxidants and
cells interact on their most fundamental levels.
This work was funded through grants from the
National Science Foundation
Environmental Molecular Science Institute and the
Large Interdisciplinary Grants Program in the
Office of Research at Ohio State.
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