A lack of the sunshine vitamin could make some RA symptoms worse or harder to treat.

Key Takeaways

Vitamin D plays a role in your body’s total health, from immune system function to bone and heart health.

Not getting enough vitamin D could make rheumatoid arthritis worse or harder to treat.

If you have a vitamin D deficiency, your doctor may recommend that you take a supplement or modify your diet. 

Vitamin D is essential for everyone, but it may be even more vital to people who have rheumatoid arthritis (RA). Many people with RA have lower levels of vitamin D than people without the condition, according to research published in the Journal of the Association of the Physicians of India in 2014. That leads some researchers to believe that not only may low levels trigger the development of RA, but they may also cause people's symptoms to worsen, too.

“As in nearly all autoimmune or chronic inflammatory diseases, it appears that lower levels of 25OH vitamin D — although there is not agreement on how low is low — are associated with a more aggressive disease or a worse response to treatments,” explains rheumatologist Carlo Selmi, MD, PhD, assistant professor of rheumatology at the University of Milan and head of the clinical immunology and autoimmunity and metabolism lab at the Humanitas Clinical and Research Center in Italy. (Autoimmune disorders are diseases in which the immune system turns against tissues in the body and damages them. These include multiple sclerosis and type 1 diabetes as well as RA.)

These were the findings of a small study of 37 people with RA who had follow-up testing a year after their diagnosis. Those who had low levels of vitamin D had increased disease activity over that year and didn't respond as quickly or effectively to treatment. The study was published in March 2015 in the journal BMC Musculoskeletal Disorders.

Besides the acknowledged role of vitamin D in bone health, researchers now know that vitamin D plays an intrinsic part in the functioning of many other systems in the body, including the immune system, according to a review of vitamin D research published in the July 2013 issue of Nutrients.

Vitamin D and the Immune System

Some evidence — mostly coming from animal studies — is available to explain what effects vitamin D could have in the immune system that influence the development of RA, says Margherita Cantorna, PhD, a distinguished professor of molecular immunology at Penn State in University Park, whose research interests include autoimmune diseases and vitamin D. According to Dr. Cantorna, vitamin D inhibits the part of your immune system that is known to cause inflammation in arthritis. Less inflammation means fewer symptoms from RA.

RELATED: 5 Illnesses Linked to Vitamin D Deficiency

Your doctor can check your levels and recommend supplemental vitamin D if necessary. Adults need 600 IU of vitamin D daily, according to recommendations from the Office of Dietary Supplements. Your doctor might recommend that you take more, depending on your overall health needs.

Since your heart health may suffer when you have RA, you may be further threatened if you're also deficient in vitamin D, says rheumatologist S. Louis Bridges, MD, PhD, professor and director of the division of clinical immunology and rheumatology at the University of Alabama in Birmingham. So, regardless of the debate about vitamin D and any direct effect on RA activity, Dr. Bridges tests his patients for vitamin D levels and recommends supplements as needed for better overall health as well as bone health.

How to Get Your Daily Vitamin D 

For many people, sunlight is an easy source of vitamin D. When your skin is exposed to ultraviolet B radiation, a compound in your skin is converted into vitamin D. But many people are missing out. Wearing sunscreen with an SPF of just 8 almost completely blocks the creation of vitamin D in your skin.

People with dark skin tones, such as African-Americans, make little vitamin D in their skin from sunlight; older people, those who are homebound, and people with digestive diseases that prevent absorption also make a decreased amount. Few foods naturally contain vitamin D, with the exception of certain oily fish and egg yolks. Milk and some other foods are now fortified with D, but may not provide enough on a daily basis.

So whether you’re worried about your bone health or about the role vitamin D plays in RA, ask your doctor about testing your vitamin D levels. You may need to modify your diet or take a supplement to see a decrease in your symptoms and help protect your bones.

Additional reporting by Madeline Vann, MPH.