What is Rheumatoid Arthritis?
Rheumatoid arthritis (RA) is a chronic autoimmune inflammatory disease that occurs when the body’s immune system attacks the body’s tissues. It predominantly impacts the lining of the joints, and affects up to 1% of adults worldwide.

What We Know About Vitamin D and Bone Health
Vitamin D (which isn’t actually a vitamin, but is instead considered a hormone) is essential to bone and muscle health. It helps our bodies absorb calcium and phosphorous – both of which are essential minerals for good bone health.

Is There a Link Between RA and Vitamin D Deficiency?
Over the last two decades, a number of studies have evaluated whether Vitamin D has an effect on rheumatoid arthritis – and what the correlation between the two may be.

At present, there is no conclusive data suggesting a 100% correlation between a lack of Vitamin D and the presence or severity of RA. There are, however, a number of studies and opinions that do state that there is a correlation – but none are 100% definitive.

Some Correlation, But Not Necessarily Causation?
Some signs seem to point to Vitamin D deficiency in those who already suffer from Rheumatoid Arthritis, but the evidence of causation remains unclear.

So what do the various studies show?
Here’s a roundup of some of the findings:

A 2014 study published in Rheumatology found that Vitamin D levels “are significantly associated with disease activity, levels of inflammatory cytokines, and bone loss in patients with rheumatoid arthritis. But the causes and development of the disease remain obscure.”The study authors noted, however, that a causal relationship can’t be established due to study design.

From a study published in Therapeutic Advances in Endocrinology and Metabolism in 2012 that evaluated a limited cohort of 44 patients: “It appears that vitamin D deficiency is highly prevalent in patients with RA, and that vitamin D deficiency may be linked to disease severity in RA. As vitamin D deficiency has been linked to diffuse musculoskeletal pain, these results have therapeutic implications. Vitamin D supplementation may be needed both for the prevention of osteoporosis as well as for pain relief in patients with RA.”

A 2016 meta-analysis published in Clinical and Experimental Rheumatology concluded: “…that serum vitamin D level is significantly low in patients with [Rheumatoid Arthritis], vitamin D deficiency is prevalent in RA patients compared to controls, and the vitamin D level correlates inversely with RA activity. Our meta-analysis suggests that the vitamin D level is associated with susceptibility to RA and RA activity.”

A limited study of 37 people with RA who had follow-up testing a year after their diagnosis – published in March 2015 in the journal BMC Musculoskeletal Disorders – found:

“These results provide further support to the immunomodulatory action of vitamin D in RA and suggest a role of basal vitamin D status in the prediction of disease evolution. Vitamin D measurement and possibly vitamin D supplementation should be considered an additional option in the management of early RA patients.”

Another study (Albert Einstein College of Medicine in New York City) pointed out that Vitamin D, essential for strong bones, is more likely to be deficient in people who take oral corticosteroids – a group which includes arthritis sufferers.

A study, published in 2004 (Arthritis & Rheumatism), supported the view that Vitamin D can play a role in preventing RA, though researchers acknowledged the results were preliminary.

A 2011 review in Seminars in Arthritis and Rheumatism evaluated several studies which looked at “the relationship between RA and vitamin D. The researchers reported they were not able to point to enough evidence to confirm low vitamin D is a risk factor for developing RA. Newer studies have disputed the claim that low vitamin D levels increase the risk for developing RA.”

Rheumatoid Arthritis & Vitamin D: More Research Needed
Many of the sources reviewed arrived at a similar conclusion: there may be some sort of link between vitamin D and Rheumatoid Arthritis in patients, but it is not well understood. To determine if there is a casual relationship, trials & studies looking at the specific effects of vitamin D supplementation on RA-related variables are needed. As U.S. News writer Maureen Donohue put it in an article in May 2017 (Is There a Relationship Between Vitamin D and Rheumatoid Arthritis?), “in the case of RA, the jury is still out.” 

Current Best Practices
Doctors, of course, have long been concerned about Vitamin D levels in patients – beyond the scope of concerns about Rheumatoid Arthritis. For patients considered at risk for conditions related to Vitamin D deficiency, they should be tested by physicians who often recommend patients take supplements (Read Institute of Medicine Guidelines Call for Increase in Vitamin D to see recent recommended values).