Vitamin
C and Blood Pressure
Several studies have found significant inverse relationships between
blood levels of vitamin C and blood pressure. However, in such
studies it has been difficult to determine whether the effect
was produced by vitamin C or some other nutrient related to vitamin
C. We designed a study to investigate the effect of low vs. normal
levels of vitamin C intake. We carefully controlled the foods
that participants were eating throughout a four-month study so
that we could distinguish the effect of vitamin C from that of
other nutrients in the diet.
We used 68 men, ages 30 to 59 years, in the study. These were
healthy non-smoking men of reasonably normal weight and no history
of high blood pressure. For one month, the men received the recommended
dietary allowance of vitamin C (60 mg) each day. Then, for one
month, their daily dose of vitamin C was reduced to 9 mg (depletion).
During the next month, they received 117 mg of vitamin C per day
(repletion). Depletion and repletion were then repeated.
We began measuring blood pressure during the ninth week of the
study, after the first depletion session had ended. Blood pressure
was measured at regular intervals for the rest of the study.
When the men received 60 mg of vitamin C per day, the level of
vitamin C in their blood actually decreased. This reduction continued
during the first depletion period. During repletion, when the
men received higher levels of vitamin C, blood levels of vitamin
C increased.
The first blood pressure measurements correlated with age, meaning
that blood pressure was higher with increasing age. There was
also a slight correlation between blood pressure and body weight.
The most remarkable correlation that we found, however, was a
highly significant inverse relationship between blood pressure
and blood levels of vitamin C level at the end of depletion. This
inverse relationship meant that blood pressure increased as blood
levels of vitamin C decreased. This correlation was much stronger
than previously reported correlations for other risk factors affecting
blood pressure.
When we grouped the men into four groups based on their blood
levels of vitamin C after depletion, we found some highly significant
differences. Blood level of vitamin C after depletion profoundly
affected the level of diastolic blood pressure (the lower number
of a blood pressure reading) throughout the rest of the study.
The effect of vitamin C on systolic blood pressure (the higher
number of a blood pressure reading) was not as strong as that
observed for diastolic blood pressure, but it was still significant.
The group with the highest blood levels of vitamin C had the lowest
systolic blood pressure for rest of the study.
We considered that vitamin C depletion may have changed the level
of some other blood pressure regulating compound. To find out
if this was the case, we measured blood levels of compounds known
to affect blood pressure, such as vitamin A, vitamin E, cholesterol
and others. Blood pressure was not related to blood levels of
any of the compounds.
We then considered that some other factor, such as age or weight,
could be influencing our results. When we re-analyzed our data
taking these factors into account, we found that the relationship
between blood pressure and blood level of vitamin C was maintained.
This meant that the effect of the vitamin C was not caused by
age or weight. In addition, food composition (for example, fiber
content, calcium, sodium etc.) did not influence the relationship.
Our study showed that the lower the blood vitamin C levels dropped
during depletion, the higher blood pressure would be for as much
as two months later. This suggests that the effect on blood pressure
was related not to the blood levels of vitamin C but on the levels
of vitamin C in the body tissues. That is, the blood levels of
vitamin C would fall more slowly if tissue stores of vitamin C
were large, because the tissue stores replenish the blood levels.
Vitamin C may exert its effect on blood pressure in a number of
ways. It may block free radicals and other substances that prevent
relaxation of small blood vessels. In addition, it may increase
the production of substances that enhance small blood vessel relaxation.
It may act directly on the blood vessels themselves. Vitamin C
may also influence blood pressure through effects on the adrenal
and pituitary glands.
The blood levels of vitamin C measured in this study were similar
to those occurring in everyday life. Even during depletion, approximately
one-third of the men had blood levels that were higher than levels
frequently found in the average population. During repletion,
the blood levels were similar to those measured in a large national
study.
Many people have very low blood levels of vitamin C because they
don’t eat enough fruits and vegetables and don’t take
vitamin C supplements. Minority populations and men seem to have
particularly low levels, but the problem is by no means limited
to those groups. Women usually have higher blood levels of vitamin
C than men, but this is thought to be related to body size. Despite
that, many women also have blood levels that are extremely low.
In conclusion, we found that the level to which blood levels of
vitamin C fell during the first episode of depletion was the most
significant factor in predicting blood pressure 4, 8, and 12 weeks
later. We feel that this reflects the amount of vitamin C stored
in the body tissues. Thus, inadequate vitamin C stores in body
tissue may be a factor in certain types of high blood pressure
disease.
Bruce Brightman – founder
LifeSource
