Vitamin C may make arthritis worse, suggests animal study
appeared to make osteoarthritis worse in guinea pigs, report the
authors of a new study.
The findings counter previous studies that have found vitamin C to be protective against osteoarthritis. A recent UK trial has linked lower intakes of fruit, vegetables, fructose and dietary vitamin C with a greater risk of developing inflammatory polyarthritis. And a previous study on guinea pigs with surgically induced osteoarthritis found that the vitamin slowed the disease down.
In the new study, published in an online issue of Arthritis & Rheumatism, the Duke University team compared the effects of eight months' exposure to low, medium, and high doses of vitamin C on the development of knee arthritis in guinea pigs.
The low dose represented the minimum amount needed to prevent scurvy. The medium dose resulted in plasma levels comparable with those achieved in a person consuming 200 mg of vitamin C daily, such as from five fruits and vegetables.
The high dose was the amount shown in the previous study of guinea pigs to slow the progression of osteoarthritis.
The guinea pigs exposed to the highest dose in the current study had more severe arthritis than the animals exposed to low or medium doses, the investigators report.
The vitamin C did indeed increase cartilage collagen content, confirming previous evidence of this effect, but it also increased the size and number of marginal osteophytes, or bony spurs produced by the body to stop the motion of the arthritic joint and deal with the degenerative process. They are found in areas affected by arthritis such as the disc or joint spaces where cartilage has deteriorated.
The team said they found expression of active transforming growth factor (TGF ) in the osteophytes, known to be activated by ascorbic acid, and also shown to cause osteoarthritis-like changes.
The researchers said their study pointed to "potential drawbacks of long-term, high-dose vitamin C intake on joint health" and suggested that people do not take supplements above the currently recommended dietary allowance - 90 mg/day for men and 75 mg/day for women.
However Paul Chamberlain, director of technical affairs at supplement manufacturer Solgar, noted that animal studies did not support immediate changes to current practice.
"You've got to bear in mind that this is one trial in the face of many other positive ones. And animal studies do not necessarily correspond to effects in humans. We would need to see more evidence of this effect," he told NutraIngredients.com.
