June 15, 2004 |
By Rebecca Ostrom for Knee1
A new study indicates that ingesting high dosages of vitamin C might not prevent osteoarthritis (OA), as was previously reported. Instead, it may actually increase the severity of the condition.
Researchers came to this conclusion after an eight-month study in which they gave guinea pigs different doses of vitamin C and noted the development of signs of OA.
Guinea pigs are an appropriate study subject because, like people, they rely on food for their vitamin C (rather than producing it in their own bodies, like some animals do). Guinea pigs also develop spontaneous osteoarthritis in their knees, as people do.
In the recent study, researchers divided 46 four-month-old guinea pigs into three groups. The researchers gave each group custom-made food with differing amounts of vitamin C in the form of ascorbic acid.
One group received 3 milligrams of vitamin C a day, the minimum amount needed to prevent scurvy. The second received 30 mg, the equivalent to its recommended daily allowance (RDA). The final group was given 150 mg of ascorbic acid per day. The equivalent in the human diet is about 2,000 mg per day.
After eight months of feeding the subjects this diet, the researchers observed the guinea pigs for signs of OA, including cartilage damage and osteophytes (bony spurs) in the knee joints. The researchers found that the guinea pigs with the least amount of vitamin C in their diet had the fewest signs of arthritis. Those with the high doses of ascorbic acid had the most symptoms.
Other factors may have played a part in the development of OA during this study. The animals that received the lowest dose of ascorbic acid in their food also weighed less, which reduces the risk of OA.
Previous studies have indicated that vitamin C might help protect against OA, but this is the first long term study and indicates that prolonged high doses may have the opposite effect. In addition, extended exposure to high levels of vitamin C seems to activate a usually-dormant protein called active transforming growth factor beta. This protein can deteriorate joints and help osteophytes form.
Vitamin C is a necessary part of the human diet. It prevents scurvy, provides antioxidants that fight disease, and promotes the formation of collagen. However, in high and prolonged doses, vitamin C may lead to diarrhea, nausea, iron problems, and kidney stones, as well as more severe OA.
The doctors who conducted the study recommend that people should not assume that more is better when it comes to vitamins and minerals. The RDA of vitamin C is 75 mg for women and 90 mg for men. These amounts can easily be achieved with five servings of fruits and vegetables per day as part of a balanced diet or with a multi-vitamin. The researchers advised against taking a vitamin C supplement in addition to a multi-vitamin.
The study, authored by Dr. Virginia B. Kraus and her colleagues at the Duke University Medical Center, was published in the June 2004 issue of Arthritis and Rheumatism.
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