Little UV Exposure, Low Vitamin D Levels Tied to Relapse Risk in AAV
Limited exposure to ultraviolet (UV) light and related drops in vitamin D levels — particularly over the winter months — may be linked to a greater risk of relapses among people with ANCA-associated vasculitis (AAV) in Ireland and the U.K., a data study found.
But vitamin D status and UV light exposure did not appear to be connected to the likelihood of having any particular AAV type.
Researchers noted that more study is needed to determine if sufficient vitamin D levels might lower a relapse risk in these patients.
The study, “The association between ambient UVB dose and ANCA-associated vasculitis relapse and onset,” was published in the journal Arthritis Research and Therapy.
Low levels of exposure to UV light, such as that coming from the sun, have been linked to AAV risk. More specifically, living at higher latitudes (i.e., farther north or south of the equator), and thereby getting less sun exposure has been linked with a higher risk of eosinophilic granulomatosis with polyangiitis (EGPA) and granulomatosis with polyangiitis (GPA), two AAV types, but not of microscopic polyangiitis (MPA).
It has been proposed that this increased risk is related to lower vitamin D levels. Produced through exposure to a certain spectrum of UV light, vitamin D has immunomodulatory properties that could influence the way autoimmune disorders like AAV manifest.
Researchers aimed to further examine the relationship between UV exposure, vitamin D status, and AAV manifestations.
They examined data from patients included in the Irish Rare Kidney Disease Registry (RKD; 439 people) to determine whether UV exposure and vitamin D status influenced the risk of AAV relapses.
Participants were followed for a median of 58.3 months (nearly five years). During this time, 135 relapses occurred in 96 people.
An estimate of exposure to UV light in the spectrum needed to produce vitamin D, called UVB, was used as a proxy measure of vitamin D status.
Analyses revealed the risk of relapse to be higher among individuals living at a higher latitude. In other words, less UV exposure was linked to a greater risk of relapse. Furthermore, lower estimated levels of vitamin D were also associated with a greater relapse risk, an effect that was most significant in wintertime.
Notably, vitamin D status specifically at the time of relapse onset was not linked to relapse risk.
“Together, these suggest that, an individual’s [vitamin D] status over a more prolonged period, particularly during winter, rather than their status peri-relapse, renders them susceptible to relapse and that multiple periods of low UVB and [vitamin D] deficiency might be contributing towards disease susceptibility,” the researchers wrote.
These findings were not linked to any particular AAV type, as had been previously suggested.
Researchers next examined data from RKD (439 people) and the U.K. and Ireland Vasculitis Rare Disease Group Registry (1,961 people) to evaluate whether UV exposure and vitamin D status were associated with the type of AAV at diagnosis.
Neither latitude nor vitamin D status were linked to the likelihood of an MPA diagnosis, or to the type of ANCA antibodies present in the blood.
The team noted, however, that this study did not evaluate the contribution of latitude or vitamin D to the overall risk of developing AAV.
“It is likely that [vitamin D] is important in de novo [new] AAV onset but may not be responsible for defining the (non-) granulomatous phenotype [AAV type],” the researchers wrote.
Overall, the findings suggest that low UVB exposure — leading to low vitamin D levels — contribute to the risk of AAV relapse.
“Prolonged low ambient UVB likely renders an individual vulnerable to a subsequent ‘hit’, which ultimately triggers disease activation,” the researchers wrote.
They noted that registry participants were predominately white and resided in a relatively narrow latitudinal range as study limitations. Data regarding individuals’ specific sun exposure, use of vitamin D supplements, sunscreen, and other factors that might influence study findings were also not collected.
Future studies should be designed to monitor vitamin D blood levels over time to more accurately assess relapse risk, and a trial of vitamin D supplement use to prevent relapses could be warranted, the team noted.