A recent study found a link between quadriceps muscle strength with both vitamin D status and knee pain among patients with knee osteoarthritis (KOA).
Osteoarthritis, also known as wear and tear arthritis, refers to a condition in which the cartilage between joints deteriorates over time. When this occurs, the bones of joints rub more closely against one another, resulting in pain and swelling. More than 27 million people in the U.S. are affected by osteoarthritis, with the knee being one of the most commonly affected joints.
Previous research has found that low vitamin D status is a risk factor for KOA. Though, the mechanism to explain this relationship remains unclear.
Quadriceps muscle strength is a major determinant of physical ability in patients with KOA. As Dr. John Cannell’s book, Athlete’s Edge: Faster, Quicker, Stronger with Vitamin D, discusses, vitamin D has been shown to play a role in muscle strength. Thus, researchers recently proposed the hypothesis that vitamin D status relates to KOA through its effects on quadriceps muscle strength.
The researchers conducted a cross-sectional study of 92 patients with KOA. Vitamin D levels, knee pain intensity and quadriceps muscle strength were assessed. This is what the researchers found:
- Higher vitamin D status was associated with greater quadriceps muscle strength (p = 0.005).
- Greater quadriceps strength was linked to less severe knee pain (p = 0.034).
- After adjusting for age, sex and body mass index, the associations remained significant.
- For each 1 ng/ml increase in vitamin D status, quadriceps muscle strength increased by 14.2% (p = 0.014).
- There was no significant association between vitamin D status and knee pain (p = 0.13).
The researchers concluded,
“On the basis of the findings of this study, vitamin D supplementation may affect pain by strengthening quadriceps muscle in KOA.”
While the researchers presented interesting findings, the study’s limitations must also be considered. First, the cross-sectional design prevented the researchers to conclude causality; thus, it is unknown whether vitamin D supplementation will strengthen quadriceps and reduce the severity of KOA. Also, the sample size was relatively small. Clinical studies are warranted to improve our understanding of vitamin D’s role in KOA.
Tovey, A. & Cannell, JJ. Researchers hypothesize vitamin D status may play a role in knee osteoarthritis by its effects on quadriceps muscle strength. The Vitamin D Council Blog & Newsletter, February, 2016.