Taking daily vitamin D doesn’t keep knee pain from getting worse or slow the loss of cartilage for people with osteoarthritis, according to a new study.
Previous research suggested that among people with the joint disorder, those with higher levels of vitamin D in their blood tended to have a slower progression of symptoms. But whether that meant taking more in supplement form would also have a protective effect was unclear.
“It looked compelling at that point,” said lead author Timothy McAlindon, from Tufts Medical Center in Boston.
For the new study, he and his colleagues randomly assigned 146 of their patients with knee osteoarthritis to take a daily dose of vitamin D or a vitamin-free placebo for two years.
None of the participants knew which type of supplement they were assigned to take. The vitamin D doses started at 2,000 international units (IU) per day and were increased to as high as 8,000 IU daily in some patients. (For most adults, the recommended daily allowance of vitamin D is 600 to 800 IU.)
The vitamin D group started out slightly worse off than their comparisons on measures of knee pain and function.
However, the vitamin didn’t seem to offer clear relief: on a 0-to-20-point pain scale, people taking vitamin D saw a 2.3-point decrease during the two years, compared to a 1.5-point decrease among those taking placebos. That small difference could have been due to chance, the researchers wrote in the Journal of the American Medical Association.
Changes in knee cartilage volume – a measure of the progression of osteoarthritis – and knee function were also similar among the two groups during and after the study period.
Osteoarthritis is typically treated with over-the-counter pain medications or steroid injections along with moderate exercise including physical therapy. For people who are overweight or obese, weight loss is recommended to take pressure off the joints.