Rheumatoid arthritis, or RA, is an inflammatory disorder in which cartilage and bone is progressively destroyed. People with RA are at increased risk for osteoporosis, fractures, deformities and disabilities. Several lines of evidence support the hypothesis that vitamin D supplementation may decrease the risk of developing RA and delay its progression. A 2009 review article in the journal, "Rheumatology" also reports that certain differences in the gene that encodes for the receptor of vitamin D influence disease susceptibility and the degree of inflammation and bone loss.
Vitamin D
Vitamin D describes a group of fat-soluble steroids, some of which are converted to the active steroid hormone form in the human body. Vitamin D3 can be obtained from synthesis in the skin, dietary sources and supplements. Vitamin D2 is found in some dietary sources and supplements. Vitamins D2 and D3 are converted in the liver to the pre-hormone, 25-hydroxylated vitamin D3, which is then transported in the blood to the kidneys where it is metabolized to the active hormone, 1,25-dihydroxyvitamin D3, or calcitriol.
Vitamin D Functions
The active hormone 1,25-dihydroxyvitamin D3 acts as a typical steroid hormone in the body. It binds to vitamin D receptors on cells, which is then transported to the nucleus as a complex. The complex binds to certain genes and influences their activity. The hormone 1,25-dihydroxyvitamin D3 regulates calcium absorption in the gut, maintains phosphate balance, plays a role in bone growth and remodeling and has several functions in the immune system, including preventing inflammation. The most common feature of persistent vitamin D deficiency in all age groups is bone softening leading to deformity and disability.
Experimental Evidence
Multiple animal studies provide evidence that the receptor for the activated hormone of vitamin D3, or VDR, is present in cells of the immune system and decreases the production of chemicals that increase inflammation. A review in the August 2008 issue of "Rheumatology" notes that vitamin D supplementation prevents the onset and progression of inflammatory arthritis in animal models. Furthermore, a study in the "Annals of the Rheumatic Diseases" reports that the VDR was localized to immune cells found in cartilage lesions in RA patients and was not found in patients without the disease.
Human Studies
The Iowa women's health study published in January 2004 in the journal "Arthritis and Rheumatism" evaluated nearly 30,000 women and found that women with a decreased intake of vitamin D had a higher risk for developing RA. Although not specific to RA patients, a review of several clinical studies in the October 2009 issue of the "British Medical Journal" reported that vitamin D supplements at doses greater than 700 international units significantly decreased falls in elderly patients. Clinical studies have not yet demonstrated that vitamin D supplementation alone or in combination with calcium supplementation significantly influences the progression of RA; however, the low cost of vitamin D supplementation, experimental evidence and human studies warrant further evaluation on the effectiveness of not only restoring vitamin D levels, but also whether substantially increasing levels of vitamin D3 improves RA severity and prevents its onset.
Recommended Treatment
Treatment for RA primarily involves nonsteroidal anti-inflammatory drugs and disease-modifying anti-rheumatic drugs, or DMARDs. Currently, treatment guidelines do not advocate vitamin D supplementation for RA. A clinical review in the August 2008 issue of "Rheumatology" notes that as of now there is not a consensus view for the optimal vitamin D replacement therapy, but recommends patients with RA and vitamin D deficiency receive high-dose vitamin D administration as an oral weekly bolus to correct vitamin D deficiency and routine lower doses to effectively maintain adequate vitamin D levels.
References
- "Rheumatology"; Genetics of Bone Loss in Rheumatoid Arthritis---Role of Vitamin D Receptor Polymorphisms; P. Ranganathan; January 2009
- "Arthritis and Rheumatism"; Vitamin D Intake is Inversely Associated with Rheumatoid Arthritis; Linda Merlino et al.; January 2004
- "Rheumatology"; Clinical Aspects of Vitamin D in the Management of Rheumatoid Arthritis; P. Leventis and S. Patel; August 2008
- "Annals of the Rheumatic Diseases"; Vitamin D Receptors in the Rheumatoid Lesion; Lynne Tetlow et al.; February 1999
- PubMed: Fall Prevention with Supplemental and Active Forms of Vitamin D
