| Genes may set response to antioxidant
vitamins
NEW YORK (Reuters Health) - New research shows that genetic make-up
strongly influences an individual's response to dietary antioxidants.
Theories that antioxidant vitamins protect against atherosclerosis,
or hardening of the arteries, have not always panned out in clinical
trials. Some studies have even linked antioxidant supplements with
a worsening effect on coronary arteries.
The new findings focus on the gene for haptoglobin, which is an
antioxidant protein that modulates the oxidative effects of hemoglobin
in body tissues.
Dr. Andrew P. Levy of Technion-Israel Institute of Technology in
Haifa and colleagues explain in the medical journal Diabetes Care
that humans have two versions of the haptoglobin gene -- HP-1 and
HP-2. The researchers theorized that differences in how the two
types function may explain paradoxical results with antioxidant
supplementation.
To investigate, Levy's team reviewed findings from a study involving
423 postmenopausal women, of whom 154 had diabetes. The women had
been randomly assigned to combined treatment with vitamin E 400
U and vitamin C 500 mg or placebo.
In particular, the researchers looked at 299 participants whose
haptoglobin type was determined and who underwent a second study
of their coronary arteries about three years after an initial exam.
They found that vitamin supplementation had a different effect
on artery narrowing depending on haptoglobin type, for the whole
group and for diabetic subjects.
Compared with diabetics taking placebo, the diameter of the arterial
lumen increased in diabetics treated with vitamins E and C who carried
the HP-1 type of haptoglobin. However, coronary diameter worsened
in those with the HP-2 type.
In women without diabetes, HP-1 had a favorable effect, too.
The authors think that in the presence of high blood sugar levels,
HP-2 haptoglobin converts vitamin C from an antioxidant into a pro-oxidant.
If their findings are validated, "haptoglobin typing may become
a useful tool to identify individuals who will benefit from antioxidant
therapy," Levy's group maintains.
SOURCE: Diabetes Care, April 2004.
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