High doses of vitamin C may worsen arthritis, at least in guinea pigs, U.S. researchers reported on Friday.

The finding by a team at Duke University Medical Center in North Carolina contradicts previous studies that suggested large doses of the vitamin may protect against osteoarthritis.

Dr. Virginia Kraus, an associate professor of medicine who led the study said the vitamin may help prevent the chemical reactions that cause damage in the short term, but become damaging in the long term.

“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,” said Kraus.

Protein activated by vitamin
Writing in the journal Arthritis & Rheumatism, her team said guinea pigs given high doses of vitamin C for eight months had more symptoms of arthritis than animals fed low or moderate doses.

Looking at the bony spurs in the animals’ knees, the researchers found a protein that leads to spur formation could be activated by vitamin C.

One obvious next step will be a study of human populations to see if people who take high doses of vitamin C also experience more arthritis. In the meantime, people may consider avoiding long-term high doses, Kraus suggested.

Recommended intakes of C for men is 90 milligrams per day and for women is 75 milligrams per day. A diet that includes five servings of fruits and vegetables a day should supply about 200 milligrams per day of vitamin C.

Some supplements contain 500 milligrams of C.