High doses of vitamin C increased the severity of spontaneous knee osteoarthritis in guinea pigs, according to a recent study by Duke University Medical Centers.
The finding contradicts earlier short-term studies in guinea pigs and an epidemiologic study in humans that suggested vitamin C and its antioxidant properties might protect against osteoarthritis, said Virginia Kraus, M.D., associate professor of medicine at Duke University Medical Center.
"It's possible that brief exposure to high levels of vitamin C offers antioxidant effects with a minimum of side effects, while prolonged exposure results in deleterious effects," she said.
The researchers fed the guinea pigs low (3 mg per day), medium (30 mg per day) and high (150 mg) doses of vitamin C over eight months. At the end of that period, they found the high dose guinea pigs developed more cartilage damage and had more bony spurs form in their knees than the other groups.
In studying the spurs, the researchers found a protein that leads to spur formation and can be activated by vitamin C.
Their conclusion, pending additional study in humans, is that people should not supplement their dietary vitamin C levels above the recommended daily allowance.
The study, sponsored by the Arthritis Foundation and the National Institutes of Health, was published in the June 2004 issue of Arthritis & Rheumatism.