Low ultraviolet B radiation, vitamin D in winter a potential risk factor for AAV relapses
Low levels of ambient ultraviolet B radiation coinciding with reduced vitamin D synthesis in winter may result in an increased risk for ANCA-associated vasculitis relapses, according to data published in Arthritis Research & Therapy.
“We were interested to investigate whether ultraviolet B radiation, mediated via vitamin D, was responsible for the geographic clustering observed in the autoimmune disease ANCA-associated vasculitis (AAV),” Mark Little, MD, of the Trinity Health Kidney Center, in Dublin, told Healio.
After hypothesizing that prolonged low ambient ultraviolet B radiation (UVB) and vitamin D deficiency are associated with the granulomatous form of the disease and an increased risk for AAV relapse, Little and colleagues analyzed patients within the United Kingdom and Ireland Vasculitis Rare Disease Group (UKIVAS) registry, as well as the national Irish Rare Kidney Disease (RKD) Registry and Biobank.
Patients were eligible for inclusion if they had a confirmed diagnosis of AAV, including a documented date and location. Confirmed diagnoses included features of granulomatosis with polyangiitis (GPA), microscopic polyangiitis (MPA) or eosinophilic granulomatosis with polyangiitis (EGPA). Additionally, positive anti-MPO or PR3 serology and diagnostic histopathology were necessary to establish a diagnosis. Patients were excluded if they had secondary vasculitis or dual anti-glomerular basement membrane disease.
The researchers used the Tropospheric Emission Monitoring Internet service to obtain daily UVB data at wavelengths for vitamin D production. Predicted vitamin D status was found for each patient by way of a specific cumulative-weighted UVB dose, which was discerned by using high-resolution date and location information.
The study was separated into two components, one consisting of AAV relapse data, and the other consisting of diagnosis data. Relapse and remission windows were defined via an algorithm taking residual disease activity and a CW-D-UVB interval of 135 days into account. For the purposes of the study, relapse was defined as the return of signs or symptoms of active vasculitis. Remission was defined as the absence of signs, symptoms and laboratory evidence of vasculitis.
According to the researchers, residential latitude correlated positively with relapse risk (OR = 1.41; 95% CI, 1.14-1.74), and average ultraviolet B spectrum-induced vitamin D synthesis correlated negatively with relapse risk (OR = 0.82; 95% CI, 0.70-0.99). In addition, there was a “stronger” correlation when the authors restricted data to winter measurements, they wrote. There were no observed correlations between phenotypes or between latitude, ultraviolet B spectrum-induced vitamin D synthesis and AAV phenotype or serology.
“Our study suggests that avoiding vitamin D deficiency may reduce relapse propensity in AAV,” Little said. “We propose a randomized control trial to test whether vitamin D sufficiency reduces relapse risk in AAV, as the next step for the vasculitis community.”
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