While a large, long-running epidemiologic study was unable to conclude that ultraviolet (UV) radiation in sunlight can cause new-onset systemic lupus erythematosus (SLE), trends in the data suggested that it could, according to findings reported in the journal Arthritis Care & Research.
Participants in the who were in the upper tertile (third) of estimated UV-B exposure had 28% higher rates of incident SLE during follow-up.
Similar numerical increases in risk with high estimated UV-B exposure were seen for specific lupus subtypes and manifestations, such as SLE with photosensitivity or with anti-Ro/La antibodies, which also fell short of statistical significance, they reported
The study’s relatively small number of new-onset SLE cases – only 297 out of about six million person-years of data – was the likely reason for the broad confidence intervals. The study did also find one lupus subtype with a statistically significant association with UV-B exposure: SLE with malar rash (HR 1.62 for top versus bottom tertile, 95% CI 1.04-2.52).
“We found no overall association between high UV radiation exposure and risk of overall SLE in these large cohorts of women prospectively followed for many years prior to SLE onset,” the researchers acknowledged.
“However, cumulative average UV radiation exposure in the highest tertile was associated with non-significant but suggestive increased risk of the subtype of SLE presenting with cutaneous antibodies, including anti-Ro and/or anti-La antibodies, and/or cutaneous involvement, including malar rash (acute cutaneous lupus) and/or photosensitivity, which tend to co-occur, and are biologically plausible,” they stated.
Photosensitivity is a hallmark of lupus, and sunlight exposure is known to cause disease flareups in people with established SLE. Among the 297 cases of incident SLE that developed in NHS participants, 58% included photosensitivity. Other risk factors include smoking and exposure to silica. Exposure to strong sunlight might be another one, since UV radiation disrupts skin keratinocytes, releasing antigens that could trigger autoimmune attack.
The decades-long American Nurses’ Health Study (NHS) I and II has the medical records of 240 000 participants, mostly female, who completed detailed questionnaires.
However, new-onset SLE is rare enough that, even with that many participants, there weren’t enough cases to be sure whether risk increases in the 30%-50% range were real.
Other major limitations included having to estimate UV exposure from participants’ residence, race serving as an inexact proxy of skin tone, and no data on sunburn history or sunscreen use.
Source: MedPage Today