Excess Vitamin C May Worsen Osteoarthritis
Researchers Say Dietary Intake Should Not Be Above the RDA Recommendation
June 3, 2004 -- It may be possible to get too much of a good
thing when it comes to vitamin C and your health.
Although heralded as a powerful antioxidant that fights
everything from the common cold to cancer, a new study shows that over a long
period of time high doses of vitamin C is associated with worsening of one of
the most common forms of arthritis -- osteoarthritis of the knee.
The study showed long-term use of vitamin C supplements
worsened the severity of osteoarthritis of the knee in guinea pigs. In these
animals, osteoarthritis of the knees is similar to the cartilage damaging
disease in humans, the authors write.
Previous short-term studies in humans and guinea pigs have
shown that vitamin C might protect against osteoarthritis of the knees. In
contrast, this new study shows prolonged use of vitamin C supplements may
Osteoarthritis causes the progressive breakdown of joint
cartilage -- a cushioning tissue layer that helps bone move against each other
without causing friction and destruction of bone.
Researchers say the study highlights the potential drawbacks of
long-term use of high-dose vitamin C supplements on joint health.
"Our findings suggest that dietary intake should not be
supplemented above the currently recommended dietary allowance: 90 milligrams
per day for men and 75 milligrams per day for women," writes researcher
Virginia B. Kraus, MD, PhD, of Duke University Medical Center, and
The study appears in the June issue of Arthritis &
Vitamin C May Raise Arthritis Risks
In the study, researchers compared the effects of eight months
of exposure to low, medium, or high doses of vitamin C in guinea pigs. Humans
and guinea pigs are among the few animals that are unable to synthesize vitamin
C for themselves.
The low dose of vitamin C was less than 3 milligrams. The
medium dose (30 milligrams) was the human equivalent of getting 200 milligrams
of vitamin C from eating five servings of fruits and vegetables a day. And the
high dose was five times higher than the medium dose and was the amount shown
in a previous study to slow the progression of osteoarthritis that is
The study showed that the high-dose group developed the most
severe osteoarthritis of the knee and showed the worse cartilage damage. In
addition the level of vitamin C (as ascorbic acid) circulating in the blood
correlated with the degree of joint damage with the animals with the highest
levels showing the most damage.
Researchers say obesity is also a known risk factor for
osteoarthritis of the knees caused by excess stress on the knee joints.
In the study the group that received the low dose of vitamin C
weighed less than the groups that received either a medium or high dose during
the latter part of the eight-month study. Therefore, they can't rule out that
lower weight may have been partially responsible for the apparent protection
from osteoarthritis in this group.
However weight differences did not account for differences in
disease severity found in the medium- and high-dose groups, which had similar
weights throughout the study. In these groups, higher blood levels of vitamin C
were associated with worsening disease.