OP0236 THE EFFECT OF UV-B RADIATION EXPOSURE ON THE RISK OF DEVELOPING RHEUMATOID ARTHRITIS
Authors: J. Hagman, B. Delcoigne, L. Klareskog, L. Alfredsson, J. Askling
Journal: Annals of the Rheumatic Diseases (2021)

Background: UV-B radiation has known immunomodulatory properties, but to what extent UV-B radiation exposure might affect the occurrence of rheumatoid arthritis (RA) has been relatively little studied, and with partially contradictory results. Objectives: To investigate the association between sun- and travel habits, as proxy markers for UV-B radiation exposure, and risk of incident RA, overall and by RA subtype. Methods: We performed a matched case-control study of 1151 incident cases with new-onset RA and 2374 population controls from the Swedish Epidemiological Investigation of Rheumatoid Arthritis (EIRA) study, recruited between 2006 and 2017. The association between sunbathing frequency, solarium use, and frequency of travels to sunnier countries than Sweden (exposures) and risk of RA (outcome) were assessed as odds ratios (OR) with 95 % confidence intervals (CI) through logistic regression, and adjusted for age, sex, residential region, year of study entry, body mass index, education, income, smoking and alcohol consumption. We further assessed effect modification by self-reported skin type, income and education, and by rheumatoid factor (RF) serostatus. Results: Overall, the frequency of sunbathing, and solarium use, were similar among RA cases and controls: ‘never doing sunbathing’ amongst RA cases vs. controls: 22% vs. 21 %, ‘sunbathing daily when possible’: 10% vs. 12%, and solarium use 13% vs. 12%. The proportion of ‘not travelled abroad to a sunnier country than Sweden during the past 5 years’ was higher for RA cases than controls: 27% vs. 23%, and ‘travelling abroad more than once a year’ was less common among RA cases: 15% vs. 20%. Sunbathing frequency was not linked to risk of RA (OR 0.91, 95% CI 0.69-1.20), nor was solarium use (OR 1.07, 95% CI 0.85-1.35). Stratification by skin type revealed no major effect modification, nor did stratification by RF status. In contrast, frequency of travel to sunnier countries than Sweden was inversely associated with RA risk comparing the most to least frequent travelers (OR 0.68, 95% CI 0.54-0.87). When stratified by educational level, this association was confined to individuals with medium (OR 0.69, 95% CI 0.48-0.98) or high (OR 0.60, 95% CI 0.50-0.91) and absent among subjects with low education (OR 1.10, 95% CI 0.56-1.99). No such interaction was observed between travel habits and income. Table 1. RA cases and controls with adjusted odds ratios and confidence intervals for overall risk of RA and by RA serostatus. N OR* for RA (95% CI ) Exposure variable RA cases Controls RF+ RF - All RA RF+ RF - Sunbathing a Never 249 495 161 85 ref ref ref At least once a month 398 844 265 124 1.05 (0.85-1.29) 1.07 (0.84-1.36) 0.98 (0.72-1.34) At least once a week 376 751 239 130 1.11 (0.90-1.38) 1.07 (0.83-1.37) 1.21 (0.88-1.66) Daily 120 278 75 43 0.91 (0.69-1.20) 0.86 (0.62-1.20) 0.96 (0.64-1.46) Travel b Never 314 537 208 103 ref ref Ref Seldom 294 568 193 97 0.98 (0.79-1.21) 0.98 (0.77-1.25) 0.98 (0.71-1.35) Once a year 359 805 227 121 0.82 (0.67-1.01) 0.80 (0.63-1.02) 0.83 (0.61-1.13) More than once a year 176 463 112 61 0.68 (0.54-0.87) 0.68 (0.51-0.91) 0.70 (0.48-1.01) Solarium c Never 991 2083 634 336 ref ref Ref Once per year or more 153 290 107 46 1.07 (0.85-1.35) 1.08 (0.83-1.40) 1.11 (0.77-1.59) OR = adjusted odds ratio, CI = confidence interval, N = number of participants, RA = rheumatoid arthritis, ref = reference, RF= rheumatoid factor. a Frequency of sunbathing if the weather invites to it? b Frequency of travels to a country sunnier than Sweden in the last 5 years? c Frequency of solarium use in the last 5 years? *Adjusting for age, sex, region, index year, BMI, smoking, alcohol consumption, education level and income. &lt;4 % of data was missing for all variables. Conclusion: Proxy markers for UV-B exposure (sunbathing frequency and solarium use within the past five years) do not seem to be strong risk factors for RA. Frequency of travels abroad was inversely associated to RA risk. The nature behind this association remains unclear. Disclosure of Interests: Johanna Hagman: None declared, Bénédicte Delcoigne: None declared, Lars Klareskog: None declared, Lars Alfredsson: None declared, Johan Askling Grant/research support from: JA acts or has acted as PI for agreements between Karolinska Institutet and the following entities, mainly in the context of the ARTIS national safety monitoring programme of immunomodulators in rheumatology: Abbvie, BMS, Eli Lilly, Merck, MSD, Pfizer, Roche, Samsung Bioepis, Sanofi, and UCB Pharma