Spondyloarthritis is any arthritis of the vertebral column. Ankylosing spondylitis (AS) is a specific inflammatory spondyloarthritis with variable involvement of peripheral joints and other organs, especially the eyes. AS is a chronic autoimmune arthritis. It can cause eventual fusion of the spine. Patients with typical features of spondyloarthritis who do not fulfill the criteria for AS are classified as having undifferentiated spondyloarthritis (uSpA).
Approximately 90% of AS patients have a gene called HLA-B27, meaning there is a strong genetic association. However, interestingly, only 5% of individuals with the HLA-B27 gene get the disease.
This raises two important questions: why don’t all HLA-B27 positive people develop AS, and also, why do some people who are HLA-B27 negative develop AS? Remember, 10% of people with AS do not have the gene.
It is thought that unknown environmental factors are responsible. Does vitamin D have anything to do with it? Let’s take a look.
Symptoms are seasonal, with fewer symptoms in the summer.
Challier B, Urlacher F, Vançon G, Lemelle I, Pourel J, Guillemin F. Is quality of life affected by season and weather conditions in ankylosing spondylitis? Clin Exp Rheumatol. 2001 May-Jun;19(3):277-81.
Occasionally rickets is misdiagnosed as AS.
Dr Sukran Erten and colleagues of the Ankara University School of Medicine in Turkey, recently studied vitamin D levels and disease activity in 161 patients with spondyloarthritis.
Erten S, Kucuksahin O, Sahin A, Altunoglu A, Akyol M, Koca C. Decreased plasma vitamin d levels in patients with undifferentiated spondyloarthritis and ankylosing spondylitis. Intern Med. 2013;52(3):339-44.
This study included 48 AS and 116 undifferentiated spondyloarthritis (uSpA) patients, along with 92 controls. The 25(OH)D means were 18 ng/ml in the AS group, 20 ng/ml in the uSpA group and 24 ng/ml in the control group. Eighty percent of AS patients, 78% of uSpA patient and 62% of control patients had vitamin D levels lower than 30 ng/mL. The 25(OH)D levels of the AS patients were significantly lower than those of the patients in the control group (p=0.004).
In the AS group, the vitamin D levels were inversely related to both erythrocyte sedimentation rate (p=0.002) and C-reactive protein (p<0.001). However, the vitamin D levels did not correlate with disease activity in either group.
The authors concluded,
“Treating vitamin D deficiency is important in patients with spondyloarthritis due to concomitant insults on tissues, including bone, in addition to the immune-modulatory effects exerted by vitamin D. It is therefore considered to be appropriate to look for vitamin D deficiency and to correct the vitamin D nutritional status in spondyloarthritis patients.”
So while there jury remains whether vitamin D plays a role in AS, one thing is apparent: people with AS are at risk for vitamin D deficiency. Thus it is wise to screen and treat vitamin D deficiency in those with AS. Further research is needed whether vitamin D plays a role in the diseases, however.