People suffering from osteoarthritis of the knee appear to receive no relief from taking vitamin D supplements, U.S. researchers report. On average 25 million Americans suffer from osteoarthritis.
"I've never heard of vitamin D as an intervention strategy," said Dr. Kevin Dalal, an assistant professor of rehabilitation medicine at the University of Miami Miller School of Medicine. "I am not surprised it didn't work. It's a tough process to try to change after it's been going on for years."
"The joints that bear the weight take the brunt of the disease. The joint space starts narrowing, bone spurs develop and the joint becomes very uncomfortable," explained Dalal, who was not involved in the study.
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He said the theory behind why vitamin D might work is its ability to increase the absorption of calcium, which might strengthen the knee joint.
The findings were to be presented Sunday at the American College of Rheumatology's annual meeting in Atlanta.
To see if vitamin D might have a beneficial effect, a team led by Dr. Timothy McAlindon, an associate professor of medicine in the division of rheumatology at Tufts New England Medical Center, studied 146 people with osteoarthritis of the knee.
The participants were randomly assigned to take vitamin D or placebo. Those taking vitamin D group started taking 2,000 International Units (IU) daily.
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Over the course of the study, doses of vitamin D were increased in 2,000 IU increments to maintain a blood level of the vitamin at more than 30 nanograms per milliliter, the researchers noted.
In addition, McAlindon's team gave the participants physical function tests and X-rayed the affected knee at the start of the study and one year later. They also had the participants undergo an MRI at the start and at the end of the study.
These data helped the researchers keep track of knee cartilage volume and thickness, along with bone marrow lesion volume, to see if there were any changes over time.
After two years, there were no substantial differences between those people taking vitamin D and those taking placebo, the researchers found.
"This study tested whether vitamin D supplementation, given over a two-year period, could influence the rate of progression of joint damage in people with knee osteoarthritis," McAlindon said in a statement. "The study found no difference compared to a placebo treatment."
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Osteoarthritis is the most common joint disease affecting middle-age and older people. The condition causes progressive damage to the joint cartilage and causes changes in the structures around the joint, the researchers said.
These changes can include accumulation of fluid, bony overgrowth, and loosening and weakness of muscles and tendons, all of which can limit movement and cause pain and swelling.
Dalal noted that the only treatment for osteoarthritis is physical therapy, exercise and anti-inflammatory medication. Eventually, many people suffering from knee osteoarthritis will need a joint replacement, he said.
Research suggests that other treatments such as glucosamine and other herbal remedies also don't work, Dalal said. "But some people are desperate and try alternatives," he said.
Causes of osteoarthritis
Treatment of osteoarthritis
Symptoms of osteoarthritis