Item #10
Effect
of Vitamin C on Blood Pressure Unclear
Two
studies yielded "diametrically opposite results.
A
paper in the December issue of Hypertension reports that long-term
vitamin C supplementation has no effect on blood pressure, while
another paper in the same journal reports that vitamin C does lower
blood pressure after 1 month in type 2 diabetics.
The
two studies yielded "diametrically opposite results," Dr.
Laura P. Svetkey, from Duke University in Durham, North Carolina, and
Dr. Catherine M. Loria, from the National Institutes of Health in
Bethesda, Maryland, note in an accompanying editorial. Therefore, it
remains unclear whether vitamin C should be recommended for the
prevention or treatment of hypertension.
However,
the most important issue, from a public health perspective, may not be
whether a particular nutrient, such a vitamin C, influences blood
pressure, the editorialists note. Instead, the "key question is
how to optimize dietary patterns to prevent and treat high blood
pressure," they suggest.
In
one study, Dr. Brian A. Mullan, from the Royal Victoria Hospital in
Belfast, Northern Ireland, and colleagues assessed the blood
pressure-related outcomes of 30 patients with type 2 diabetes who were
randomized to receive vitamin C 500 mg or placebo once daily for 4
weeks.
Vitamin
C use was associated with significant reductions in brachial systolic
and diastolic blood pressures. In addition, vitamin C was linked to
improvements in arterial stiffness. In contrast, placebo use was not
tied to any hemodynamic effects.
In
the other study, Japanese researchers assessed the blood pressure
effects of vitamin C use in 378 patients with atrophic gastritis. The
group included 244 subjects who received either 50- or 500-mg vitamin
C supplementation for 5 years and 134 subjects who did not receive the
supplement.
During
the study period, all of the groups experienced similar significant
increases in systolic blood pressure compared with baseline values.
Furthermore, diastolic blood pressure changes were also similar for
the three groups. The lack of an association between vitamin C use and
blood pressure held true even after accounting for antihypertensive
drug use and smoking status.
Because
the study populations and treatment durations were different, it is
difficult to compare the findings from the two studies, Dr. Svetkey
and Dr. Loria note.
Instead
of testing the effect of a single nutrient, "perhaps we need to
approach dietary research from the opposite direction, first testing
which combination of foods...lower blood pressure or prevent the
age-related rise in blood pressure," the editorialists state.
After this has been done, then "we can begin disentangle the
effects of individual nutrients," they add. Hypertension
2002;40:797-803
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