New Study Adds Confusion Around Vitamin D Supplements
You may have read the headlines—vitamin D supplements do not prevent knee osteoarthritis or reduce pain. But that does not tell the whole story, and illustrates the need for proper commentary when evaluating medical research.
It is true that a new study found that vitamin D supplements for people with knee osteoarthritis and low vitamin D levels did not reduce knee pain or slow cartilage loss.1 However, the researchers from the University of Tasmania chose very low vitamin D levels as their treatment goal.
The researchers chose "24 ng/mL as an indication that vitamin D supplementation was successful—well below the normal range for vitamin D levels, which is is between 32 ng/mL and 100 ng/mL,” noted David R. Seaman, DC, MS, Professor of Clinical Sciences at the National University of Health Sciences in Pinellas Park, Florida, who was not involved in the new study.
“Most vitamin D researchers suggest 40 ng/mL or more as the goal,” noted Dr. Seaman. The fact that participants did not have changes in knee pain or cartilage loss may be more of a reflection of their low vitamin D levels at the end of the study, rather than the ineffectiveness of vitamin D, he said.
Previous research has found vitamin D deficiency can lead to loss of cartilage volume and pain in the knee, which increases the risk of osteoarthritis. Knee osteoarthritis occurs in an estimated 10% of men and 13% of women over age 60.
Vitamin D can reduce bone turnover—the constant tearing down and rebuilding of bone. Change in the rate of bone turnover is an important determinant of bone disease. Vitamin D has also been shown to reduce degrading of knee cartilage, according to Changhai Ding, MD, PhD, lead author the current study and of a 2009 study that found low levels of vitamin D were associated with the loss of cartilage in the knee joint of older people.2
Previous observational studies have suggested that vitamin D supplementation is associated with benefits for knee osteoarthritis, but evidence from clinical trials has been contradictory, Dr. Ding noted.
In the new study, Dr. Ding and colleagues randomly assigned 413 patients with symptomatic knee osteoarthritis and low vitamin D levels to receive monthly treatment with oral vitamin D3 (50,000 IU) or an identical placebo for 2 years. Their average age was 63.
Of the 413 participants, 340 completed the study. The researchers found vitamin D supplements, compared with placebo, did not significantly slow knee cartilage loss (as measured by MRI) or reduce knee pain over 2 years. The researchers measured different types of knee pain, including pain when walking on the flat surface, going up/down stairs, at night, sitting/lying and standing upright. Vitamin D levels did increase more in the vitamin D group than in the placebo group over 2 years, the researchers found.
“These data suggest a lack of evidence to support vitamin D supplementation for slowing disease progression or structural change in knee osteoarthritis,” Dr. Ding wrote.
However, in an email, Dr. Ding told Practical Pain Management he plans to report at the upcoming 2016 World Congress on Osteoarthritis in Amsterdam that a post-hoc analysis revealed that vitamin D supplementation significantly reduced MRI-assessed knee joint effusion (an abnormal accumulation of fluid in or around the joint) in patients with knee osteoarthritis. The findings “suggest that further studies with different outcome measures are required to determine the effects of vitamin D supplementation on knee osteoarthritis,” he said.
OA is a Metabolic Disease
“Osteoarthritis is a metabolic disease, not simply a result of wear and tear,” Dr. Seaman said. The current study attempts to treat a complex disease with one therapy, he noted.
Dr. Seaman noted the patients in the study had an average body mass index of 29.6, which means they were borderline obese. “You can’t give people with osteoarthritis of the knee, who are overweight, one single therapy and expect it to work,” he said. “You need to change more than one thing.”
He observed that a chronic inflammatory condition like osteoarthritis should involve multiple treatment interventions, including weight loss, eating anti-inflammatory foods (particularly vegetation), and taking nutritional supplements such as glucosamine/chondroitin, magnesium, fish oil, ginger/tumeric, and vitamin D.