Objectives: To examine associations between sunlight exposure and anti-citrullinated protein antibodies (ACPA) using general population data in Quebec, Canada.
Methods: A random sample of 7600 individuals (including 786 positive ACPA subjects and 201 self-reported rheumatoid arthritis, RA cases) from the CARTaGENE cohort was studied cross-sectionally. All subjects were nested in four census metropolitan areas, and mixed-effects logistic regression models were used to calculate odds ratios (OR) and 95% confidence intervals (CIs) for ACPA positivity related to sunlight exposure, adjusting for sun-block use, industrial fine particulate matter (PM2.5 ) exposures, smoking, age, sex, French Canadian ancestry, and family income. We also performed sensitivity analyses excluding subjects with RA, defining ACPA positivity by higher titers, and stratifying by age and sex.
Results: The adjusted ORs and 95% CIs did not suggest conclusive associations between ACPA and sunlight exposure or sun-block use, but robust positive relationships were observed between industrial PM2.5 emissions and ACPA (OR 1.19 per µg/m3 , 95% CI 1.03 - 1.36 in primary analyses).
Conclusions: We did not see clear links between ACPA and sunlight exposure or sun-block use, but we did note positive associations with industrial PM2.5 . Future studies of sunlight and RA (or ACPA) should take air pollution exposures into account.
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