To examine associations between sunlight exposure and anti-citrullinated protein antibodies (ACPA) using general population data in Quebec, Canada.
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 (PM ) 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.
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 PM emissions and ACPA (OR 1.19 per µg/m , 95% CI 1.03 – 1.36 in primary analyses).
We did not see clear links between ACPA and sunlight exposure or sun-block use, but we did note positive associations with industrial PM . Future studies of sunlight and RA (or ACPA) should take air pollution exposures into account.

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