THURSDAY, June 3, 2004 (HealthDayNews) -- If a moderate amount of daily vitamin C is good for bone health, then more must be even better, right?
"Everybody needs vitamin C in their diet, but taking supplements beyond the recommended daily allowance is probably inadvisable" when it comes to fighting arthritis, said Dr. Virginia Kraus, an associate professor of medicine at Duke University and lead author of a study that challenges the conventional wisdom on diet and osteoarthritis.
Millions of older Americans suffer from the pain and stiffness of osteoarthritis -- a deterioration of bones and cartilage in the joints. Unlike rheumatoid arthritis, which experts know is caused by inflammation brought on by immune system dysfunction, the causes of osteoarthritis remain unclear.
Seeking a deeper understanding of the disease, researchers are now focusing on lifestyle and dietary factors as possible contributors to osteoarthritis. In their study, published in the June issue of Arthritis & Rheumatism, Kraus' team of researchers fed guinea pigs low, medium and high doses of vitamin C as part of their daily diet.
"The guinea pig is the ideal animal in which to test this," Kraus explained, "because they require vitamin C in their diet, just like humans, and they get an osteoarthritis of their knees that looks very similar to the type of knee osteoarthritis that humans get."
Arthritis specialists have long recommended that patients consume an adequate daily amount of vitamin C because the nutrient is both a potent antioxidant and a key player in the formation of joint cartilage. But would higher doses of the vitamin make bones even stronger?
Not so, Kraus reports. "More is not better," she said. "We found that the more vitamin C given, the more osteoarthritis is apparent in the joints of these animals that are predisposed to getting osteoarthritis."
Guinea pigs fed low doses of vitamin C showed the least signs of knee arthritis, Kraus said, but since they also tended to weigh much less than the medium- or high-dose animals, reductions in weight might explain that result.
Animals fed a medium dose of vitamin C -- roughly equivalent to the recommended daily allowance in humans -- had slightly more signs of knee damage. But it was the high-dose animals that fared worse, with obvious signs of arthritis and an increase of bony outcroppings on the knee called osteophytes or bone spurs.
The exact links between excess vitamin C and osteoarthritis remains unclear. "One connection that we were able to make was that vitamin C activates a protein called TGF-beta," Kraus said. "When active, this protein seems to increase bone spur or osteophyte formation." Microscopic bone spurs roughen the surface of joints, she explained, triggering the irritation and inflammation that is a hallmark of arthritis.
Dr. John H. Klippel, president of the American Arthritis Foundation, said the findings "are challenging the common wisdom that increased doses of vitamin C may be helpful or protective -- in fact, it seems to be quite the opposite." He believes more study is needed into possible links between diet and bone health, especially since the origins of osteoarthritis remain a mystery.
"This kind of research is so important because osteoarthritis is an extremely common disease," he said. "Therefore, it begs the question, are there other dietary influences that in some way affect this disease?"
The study findings should not alter the standard dietary recommendation that Americans eat five to six servings of fruits and vegetables per day to obtain adequate doses of vitamin C, Kraus said. But for those who can't always be sure they are getting enough vitamin C from their diet, taking a daily multivitamin might be advisable, as well.
"What I tell my patients is that one multivitamin per day is a prudent thing because it also has the daily allowance of vitamin D and other micronutrients that might be important to bones," she said.
But should folks take an extra vitamin C pill on top of that?
"Absolutely not," Kraus said. "I try and emphasize to my patients that just because something is natural doesn't mean that more is better for you. It just goes to prove that the old adage that moderation is, for most things, the best."
For more details on the connections between diet and arthritis, go to the Arthritis Foundation.