How Does Vitamin D Affect
Rheumatoid Arthritis?

There are several different types of arthritis with varying causes and symptoms. Osteoarthritis is the most common form and is caused by wear and tear on joints over time from overuse. Rheumatoid arthritis (RA) is an autoimmune, inflammatory disease in which the body’s immune system mistakenly attacks healthy body cells, causing inflammation. In rheumatoid arthritis, this inflammation usually occurs in the joints and can cause both joint and tissue damage. Since RA is not caused by overuse of a joint over time, it often develops at a younger age than osteoarthritis. Rheumatoid arthritis can develop at any age but usually appears between ages 30-50.[1] Juvenile idiopathic arthritis, formerly known as juvenile rheumatoid arthritis, is the most common form of arthritis in children.[2]

Although the cause of rheumatoid arthritis is unknown, there is evidence that infection, genes, and hormone changes may be linked.[3] The primary symptoms are joints that are painful, stiff, and have loss in range of motion. Other symptoms can include sleep difficulties, chest pain, dry eyes and mouth, itchy or burning eyes, and tingling or burning in the hands or feet. It has been calculated that approximately 1.5 million Americans have RA and it is 2.5 times more prevalent among women.[4] 

How does vitamin D affect rheumatoid arthritis?

Low levels of vitamin D have been linked to increased risk and activity of a variety of autoimmune conditions including rheumatoid arthritis, multiple sclerosis, diabetes mellitus and inflammatory bowel disease. Research suggests that there may be an association between vitamin D deficiency, juvenile arthritis, and inflammatory arthritis. Some studies have suggested that vitamin D could help manage inflammation related to arthritis, due to the role vitamin D plays in regulating immune and inflammatory responses in the body. 

Vitamin D acts as an immune system modulator by suppressing inflammation associated with both the innate and adaptive immune response.[5] Studies have shown that vitamin D plays a role in both the activation of immune cells for helping the body fight off infections, and also in suppressing immune response in cases of hyperinflammation. This excessive inflammation is what happens in the body in cases of rheumatoid arthritis. In response to foreign pathogens, the immune system releases small proteins called cytokines, which trigger an immune response to help fight off infections. Sometimes this response goes into overdrive and excessive amounts of cytokines are released. This is known as a cytokine storm and can cause hyperinflammation. Vitamin D decreases inflammation by suppressing the production of inflammatory cytokine cells and facilitating the production of anti-inflammatory cytokine cells.[5,6] 

One study looking at the correlation between vitamin D and reactive oxygen species found that those with rheumatoid arthritis had lower levels of vitamin D and higher levels of reactive oxygen species and inflammatory cytokines than the control group.[7]

Is vitamin D good for arthritis?

Several scientific studies have identified a link between low vitamin D level and rheumatoid arthritis, and it is common for those with rheumatoid arthritis to have a vitamin D deficiency. Vitamin D receptor gene research reveals an association with RA susceptibility and severity.[8,9] 

Studies looking at vitamin D and rheumatoid arthritis have suggested that having higher levels of vitamin D may help prevent RA onset.[10,11] A study that followed 29,368 women over 11 years found that greater intake of vitamin D was inversely associated with risk of developing rheumatoid arthritis.[11]

Research also shows that lower serum vitamin D is associated with increased rheumatoid arthritis disease activity, pain and functional disability.[12] One study of 1,191 RA patients found that lower levels of vitamin D were correlated with more severe disease activity and disability as measured by the Health Assessment Questionnaire Disability Index, Disease Activity Score (DAS28), and Mobility Activities of Daily Living Score.[13] Another study comparing 50 RA patients and 50 controls found that 84% of RA patients were vitamin D deficient versus only 34% of controls. Additionally, in this study vitamin D level was correlated to disease severity, with patients who had lower vitamin D levels having higher disease activity. 

A study out of Canada found that amongst those with RA, having a low level of vitamin D was associated with over 5 times higher disease activity compared to those with adequate vitamin D levels.[14] A study that measured C-reactive protein (CRP) and Erythrocyte Sedimentation Rate (ESR), indicators of inflammation, in RA patients found that lower levels of vitamin D were associated with higher Disease Activity Scores (DAS28) and higher levels of inflammatory markers.[15]

Why is vitamin D important for arthritis?

Vitamin D is produced in the skin when the body is exposed to sunlight, specifically light in the UVB light spectrum. This same spectrum of light also produces several other hormones and peptides that contribute to systemic health and wellness. Substances made from chemical reactions with sunlight are called photoproducts. While vitamin D is the most universally recognized health benefit humans receive from sun exposure, it is just one of many important photoproducts. 

In addition to vitamin D, other healthy photoproducts made in the same UVB wavelength range include: Calcitonin Gene Related Peptide, Neuropeptide Substance P, Adrenocorticotropic Hormone, Melanocyte Stimulating Hormone, Calcitriol, and Beta Endorphin. These photoproducts have widespread impact on the body and are involved in regulating the immune system, promoting proper blood flow, reducing inflammation, acting as natural pain killers, and more.

The correlation between higher blood levels of vitamin D and disease prevention in many epidemiological studies is actually measuring sun exposure and not supplemental vitamin D. Population studies have repeatedly demonstrated that sun exposure is a larger contributor of vitamin D concentration than oral consumption.[16,17] Therefore, at a population level, vitamin D is actually a measure of sun exposure, and higher serum concentrations are an indicator of greater skin contact with the sun’s light.[18] 

The assumption that vitamin D level in the body from an oral supplement represents the same health benefits as vitamin D derived from light fails to take into consideration the impact sunlight has on human health outside of vitamin D production. It is important to consider that there are other vital photoproducts that contribute to our systemic health in addition to vitamin D.  

Some studies have started looking not just at vitamin D level and supplementation, but at the amount of UVB exposure someone has and its impact on rheumatoid arthritis. A study that looked at the impact of seasonality on RA activity found that disease activity was higher in the spring and lower during the fall.[20] This pattern could potentially be impacted by vitamin D levels which tend to peak in the early fall after the sunny summer months and then reach a low near the end of winter. One study looking at 106,368 women aged 30-55 found that higher cumulative UVB exposure was correlated to a decreased risk of RA, with those in the highest UVB exposure category having a 21% RA risk reduction compared to those in the lowest category.[19] 

Vitamin D as a potential arthritis treatment 

More research is needed to determine the potential of vitamin D as a rheumatoid arthritis treatment, and the exact vitamin D form and dosage required for improving arthritis. High dose oral vitamin D supplements have the potential to cause harm, and therefore it is important to consider what is a safe and appropriate dose.  

The Institute of Medicine’s (IOM) recommended dietary allowance for vitamin D is 600 International Units (IU) per day. This recommendation is based on what is needed to prevent rickets and osteoporosis. Many vitamin D researchers disagree with this recommendation and say that the IOM’s recommended allowance isn’t enough to prevent deficiency or support bone health. Generally, 4,000 IU or less per day is considered safe, as long as your blood values are being monitored. It is important to avoid excessive doses of oral vitamin D. If vitamin D intake is too high, it can cause elevated blood calcium levels and potentially dangerous consequences.

Obtaining vitamin D from light allows your body to self-regulate vitamin D production and make as much as it needs to stay healthy, without any risk of overdose or toxicity. Unlike with oral supplements, you cannot overdose on vitamin D produced in your skin. If you have enough vitamin D, your body will simply produce less.