Despite a setback from
a couple of studies that dive-bombed beta-carotene’s place in the sun as an
anti-lung cancer fix (the National Cancer Institute studies using beta-carotene
on smokers resulted in a no-benefit-and-maybe-harm result, causing one of the
studies to be interrupted), antioxidants are still being studied, as are
several phytochemicals that appear to act as vitamin precursors. The
beta-carotene study, while creating a flurry among U.S. researchers, developed
into something much more serious in Scandinavia, where the Finnish
alpha-tocopherol beta-carotene lung cancer prevention trial showed harm to
smokers who were given supplemental beta-carotene.
Danish health minister
Yvonne Anderson demanded a warning label on all supplements that include
beta-carotene to warn smokers about possible harm. Denmark called on the
European Union to review beta-carotene’s status as an approved food color
additive, which could require its removal as the coloring material for margarine,
candy, soda and other products.
Mary Burnette,
spokesperson for the Council for Responsible Nutrition, the trade association
for the U.S. dietary supplement industry, believes the Danish move was a “major
overreaction.”
ABCs of vitamin
E
Vitamin E is a potent
peroxyl scavenger. It terminates the chain reaction of lipid peroxidation,
according to studies completed at the University of California at Berkeley.
Lester Packer is the principal investigator of the vitamin E group, along with
Maret Traber. Their studies show that the antioxidant function of vitamin E is
potentiated in the body by other antioxidants. The tocopheroxyl radical is
reduced by ascorbate, which is then oxidized and can be reduced by thiol
antioxidants such as glutathione and dihydrolipoic acid (DHLA), a hot button of
its own.
How can we be sure of
the efficacy of vitamin E? Until its function is more clearly understood, it
will be difficult to determine precisely how the vitamin works, and to be sure
that some of the effects aren’t negative. The use of vitamin E as a supplement
or as an ingredient to fortify foods will remain controversial until the way
the material works is clearly understood.
The vitamin E group at
Berkeley is investigating the function of vitamin E by using alpha-lipoic acid,
which has been shown in previous studies to prevent the development of vitamin
E deficiency symptoms in laboratory animals. If vitamin E’s sole function is
that of an antioxidant, alpha-lipoic acid should replace vitamin E in the
studies. But if there are reactions between alpha-tocopherol and other
nutrients indicating that vitamin E has a structure-specific role, the reaction
could be defective. If tissue alpha-tocopherol concentrations are maintained in
the presence of alpha-lipoic acid, then regeneration of vitamin E from the
vitamin E radical is a relevant potentiator of the function of the vitamin.
Figuring out
phytochemicals
According to a
statement from the National Cancer Society, the group supports a total diet
concept: A balanced diet that contains many different foods is necessary for
good health. Still, the society states, some phytochemicals apparently do act
to prevent cancer better than others. The NCS supports several studies on these
food components, including a study of carotenoids related to vitamin A by
Matthew Longnecker of the University of California at Los Angeles to measure
certain dietary factors relating to cancer risk, and long-range studies by
Walter Willett (Harvard’s School of Public Health) on dietary pattern and its
relationship to heart disease and cancer.
Maybe because it’s
been suggested that increased consumption of antioxidants can improve a
person’s appearance and performance immediately, antioxidant compounds have
gained a certain panache. The DSHEA (Dietary Supplements Health and Education
Act) has permitted a number of sports drinks, sports bars, and other products
to appear, chock-a-block with various compounds that are probably antioxidants.
Some are herbal compounds that are very likely precursors to some of the
antioxidant vitamins, and some are flavanoids, the secondary plant metabolites
present in fruits and vegetables.
Just how effective are
antioxidants in preventing cells from being damaged by free radicals? The
studies aren’t really far enough along to tell. But clearly, increased
consumption of fruits and vegetables, with carefully planned supplements, seems
to be warranted. Consumption of vitamin C is below the Recommended Daily
Intake, according to USDA’s consumption studies, and vitamin A may also be low.
Vitamin D is particularly short in the elderly and in northern climates, and
increasingly so as sun-worshipping goes out of vogue. Smoking ‘depletes vitamin
C, which appears to be effective in stoking up the immune system.
The role of these
vitamins is still controversial. But the RDI for vitamin consumption is rarely
met overall, so there is room within current guidelines to develop foods and
supplement products that are unlikely to cause overdose of even the fat-soluble
vitamins (A and D) that could build up in the body. increased use of
vitamin-rich vegetables as ingredients can permit a vitamin-rich label
statement on conventional foods.
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