Rheumatoid arthritis (RA) is an autoimmune disease, meaning the body attacks its tissues, leading to joint destruction that may cause deformity and disability in the affected joints. Vitamin D is a nutrient that has been shown to have important functions in immune activity as well as bone health. However, people with RA tend to have low levels of vitamin D and are more likely to have low vitamin D levels than people without RA, suggesting a link between vitamin D and RA.

Research is mixed on whether vitamin D supplementation improves RA, although some evidence suggests that increasing vitamin D levels in the body may help control symptoms and disease activity. People with RA have a higher risk for osteopenia and osteoporosis. Vitamin D is an important factor in promoting bone health. Therefore, vitamin D is particularly important for people with RA.

What Is Vitamin D?

Vitamin D is a nutrient that your body needs to make your muscles move, help your nerves send signals, and allow your immune system to fight off bacteria and viruses that can make you sick. Vitamin D is also needed so that bones can absorb the calcium they need to be strong and healthy.

There are two kinds of vitamin D: Vitamin D₂ or Vitamin D₃. Vitamin D₂ can mostly be found in plants, mushrooms, and yeast. Vitamin D₃ can be found in oily fish and is also made in the body during sun exposure. According to the Cleveland Clinic, foods that are good sources of vitamin D include:

• Beef liver
• Fortified cereal
• Fish (such as salmon, sardines, swordfish, and cod liver oil)
• Egg yolks
• Fortified milk and orange juice

Your body breaks vitamin D down into its active form, called 1,25-dihydroxyvitamin D — which is also known as calcitriol and can be found as a supplement. This active form of vitamin D can affect the cells involved in the immune system.

How Does Vitamin D Affect the Immune System?

Vitamin D is important for a healthy immune system by affecting the function of two important immune cell types, called B cells and T cells, that play a role in RA. These cells have a vitamin D receptor that binds to active vitamin D. When vitamin D binds to the receptor, it changes how the immune cells behave. Vitamin D is described as “immunomodulatory,” meaning it can modulate (change or affect) the immune system.

B Cells and Vitamin D

B cells are responsible for making antibodies that can bind to and help destroy viruses and bacteria. Sometimes, B cells mistakenly make antibodies that attack the body’s tissues, which causes autoimmune diseases like RA. Active vitamin D can control B-cell activity, which may limit the creation of autoantibodies that can lead to autoimmune diseases.

T Cells and Vitamin D

T cells can increase inflammation and kill cells that are infected with viruses or bacteria. Some T cells drive inflammation. Other T cells, called regulatory T cells, limit the immune response and inflammation. If the balance between them is thrown off and regulatory T cells cannot turn off the immune response, inflammatory diseases like RA can result.

Vitamin D has two important roles in this process. Vitamin D can help limit the T cells that drive inflammation, and it can also increase the activity of regulatory T cells that turn off the immune response. By restoring the balance between T cells, vitamin D can help prevent autoimmunity and inflammation.

Vitamin D Levels in People With RA

Low vitamin D levels have been associated with worse outcomes in people with RA. A 2016 meta-analysis analyzing serum vitamin D levels (levels of vitamin D in the blood) found that people with RA had much lower vitamin D levels and were more likely to have a vitamin D deficiency than their healthy peers were. Another study found that 84 percent of people with RA had a vitamin D deficiency compared to 34 percent of people in the healthy group. Lower vitamin D levels also correlated with a higher severity of RA — people with the lowest level of vitamin D had the highest disease activity.

Does Vitamin D Supplementation Help RA?

Although evidence seems to suggest an important role of vitamin D in RA, research is mixed on the effect of vitamin D supplementation in improving outcomes.

A 2016 review of existing trials found no strong evidence that vitamin D supplementation helped prevent or treat RA. Later, a 2017 review of other research concluded that vitamin D supplementation might lower the disease activity score in RA, but more clinical trials were needed to be sure.

Since that review, several clinical trials have studied the effects of vitamin D in people with RA.

In one study, people with RA were given high doses of vitamin D for six months. Then, researchers measured functional disability using the health assessment questionnaire and markers of inflammation (ESR and CRP). The researchers found that vitamin D supplementation reduced disability and inflammation (according to ESR and CRP levels), but did not reduce reported pain and fatigue.

Another clinical study measured how adding vitamin D supplementation affected people with early rheumatoid arthritis. People with RA using vitamin D with their standard treatment reported better overall health in a global health assessment than people who used standard treatment alone.

The Bottom Line

Overall, scientists don’t know for sure if vitamin D supplements can treat RA, but there is evidence that vitamin D supplementation can help relieve some symptoms. Taking vitamin D supplements is especially important for those with vitamin D deficiency to keep bones strong and help the immune system function properly.

Supplementing Vitamin D

Vitamin D supplementation may be important in people with vitamin D deficiency, which is common in people with RA. If you’re interested in increasing your vitamin D intake, know that there are some risks you should consider alongside the potential benefits.

Although vitamin D is important for good health, taking too much (which typically occurs from using supplements, not diet) can have negative impacts. The Office of Dietary Supplements says that too much vitamin D can cause nausea and vomiting, muscle weakness, confusion, pain, dehydration, and kidney stones. Vitamin D can also interact with some medications.

Talk to your doctor before adding supplements to your diet. If you are concerned about your vitamin D levels, talk with your doctor for their suggestions. A healthy diet and exercise are also important for getting enough vitamin D and managing RA.

Talk With People Who Understand

On myRAteam, the social network and online support group for people with rheumatoid arthritis and their loved ones, members discuss the chronic nature of the disease. Here, more than 147,000 members from across the world come together to ask questions, offer advice and support, and share stories with others who understand life with RA.

Are you using vitamin D to help with RA symptoms? Share your experience in the comments below, or share your story on myRAteam.