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Can you get too much Vitamin C? News headlines suggested as
much following a presentation at an American Heart Association
conference earlier this year. The research that started the
fuss surveyed 573 men and women about their Vitamin C intake
before and after an 18-month period. Those who said they took
20-190 mg per day showed little change, those who reported
taking 192-479 mg daily had more than twice the normal rate
of artery wall thickening, and those taking 480-3,355 mg per
day had 2.7 times the rate of thickening. Strangely enough,
only supplemental, not dietary Vitamin C was associated with
faster artery thickening.
This new report is considered scary because its the first
trial testing Vitamin C’s effects on arteries in the
same people over time the first longitudinal study. Even so,
the study is contradicted by an even bigger study done in
2004. While not longitudinal, it found that individuals with
high Vitamin C intake actually have thinner arteries than
those with low intake (after many adjustments due to variables),
although for some reason the result only held for subjects
over the age of 55. A third study found no change in artery
wall thickness due to Vitamin C supplementation.
With so much other evidence to suggest that Vitamin C fights
heart disease it relaxes blood vessels, reduces LDL cholesterol
oxidation, etc., we’re left to wonder how the negative
result was obtained. Remember, however, that the report is
still preliminary. A more detailed description of what the
scientists actually saw, combined with the criticisms and
insights of other scientists (a process called peer review)
may unearth more clues.
Furthermore, the trial measured artery wall thickness, not
incidence of heart attacks. This begs the question, “Is
thickening of artery walls necessarily a bad thing?”
If it’s due to cholesterol buildup, sure. If it’s
due to more connective tissue, though, it may actually be
good, it depends on which layer of the carotid artery wall
is involved: outer, middle or inner. If the middle layer is
thickened, that’s probably good; it’s rich in
stretchy connective tissue. Indeed, fortification of artery
walls with connective tissue is one reason why estrogen replacement
therapy (ERT) may fight heart disease in postmenopausal women;
ERT thickens the middle carotid artery wall and reduces heart
disease at the same time. If Vitamin C also fortifies artery
walls by promoting collagen synthesis, for example, it may
be doing us good.
On the other hand, if Vitamin C thickens the inner carotid
artery wall, it could indeed promote the growth of atherosclerotic
plaques, bad news. Since the researchers lumped together both
inner and middle artery wall thicknesses as one big measurement,
however, we don’t know whether Vitamin C may cause good
artery wall thickening or bad. Along with Vitamin C’s
proven benefits and the National Research Council’s
recent establishment of 2,000 mg as an upper daily limit for
the vitamin, this makes it inadvisable to flush your Vitamin
C pills down the toilet.
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