A study published in the journal Rheumatology has found that vitamin D levels are significantly associated with disease activity, levels of inflammatory cytokines, and bone loss in patients with rheumatoid arthritis.
Rheumatoid arthritis (RA) is an autoimmune disease that results in chronic inflammation predominantly of the flexible joints. RA affects up to 1% of adults worldwide. Bone erosion, or osteoporosis, is a characteristic of the disease. The causes and development of the disease remain obscure.
Multiple studies have shown that compared to healthy controls, patients with RA have lower vitamin D levels. Some studies observing the relationship between vitamin D levels and RA disease activity have found an association between the two, while others have not.
Research has determined that vitamin D works with the immune system by regulating immune cells that produce inflammatory or anti-inflammatory proteins called cytokines.
Interleukin-17 (IL-17) and interleukin-23 (IL-23) are two pro-inflammatory cytokines that are implicated in the inflammatory response in autoimmune diseases. Studies have shown that increased levels of these cytokines are associated with increased RA disease activity, but there is no evidence to show whether vitamin D status is associated with these cytokines in patients with RA.
Recently, Dr. Qiong Hong and colleagues conducted a study to compare vitamin D status with levels of cytokines, disease severity, and degree of bone loss in patients with RA. They aimed to determine if vitamin D levels were associated with any of these factors related to RA.
The study included 130 patients with RA recruited from a hospital in China, who were matched by 80 healthy individuals recruited from the local community.
All the RA patients were classified into three groups according to their Disease Activity Score in 28 joints (DAS28): low (DAS28 5.1). DAS28 is a quantitative measurement of disease activity used to monitor the treatment of rheumatoid arthritis.
In addition to DAS28, other quantitative measurements used to assess disease activity were taken. These included morning stiffness time, tender joint count (TJC), swollen joint count (SJC) and Health Assessment Questionnaire (HAQ) score. An increase in these measurements indicate increased disease severity.
Measurements of vitamin D levels, IL-17 and IL-23 levels, bone mineral density (BMD), and bone erosion were also taken.
The research team wanted to see how vitamin D status was related to IL-17 and IL-23, disease severity, and bone loss in RA patients.
Statistical analyses showed the following results:
- RA patients had significantly lower vitamin D levels compared to controls.
- Vitamin D levels were significantly negatively associated with DAS28, morning stiffness time, TJC, SJC, and HAQ score.
- Vitamin D levels were significantly negatively associated with IL-17 and IL-23 levels.
- In RA patients, individuals with osteoporosis and osteopenia had significantly lower vitamin D levels than patients with normal BMD.
The researchers concluded,
“In RA patients, lower levels of 25(OH)D were associated with increased disease activity, including SJC, TJC, joint pain degree, morning stiffness time and HAQ score. Serum levels of 25(OH)D were also negatively associated with DAS28 score, ESR, platelets, IL-17 and IL-23. Furthermore, patients with [osteoporosis] and osteopenia had significantly lower levels of 25(OH)D than those with normal BMD.”
It is important to note that a causal relationship can’t be established due to the case-control and cross-sectional designs utilized in the study. Other confounding factors such as smoking and medications, were not accounted for, which further limits the conclusions of the study.
This study provides an expanded picture of the link between vitamin D and inflammatory cytokines, disease activity, and BMD in RA patients. Still, trials looking at the effect of vitamin D supplementation on these variables are needed to determine if a causal relationship exists.