Abstract
Background Whether ultraviolet radiation (UV) exposure is a risk factor for the occurrence of Systemic Lupus Erythematosus (SLE) or of flares remains unclear. Classically, it has been thought that sun exposure is a risk factor for developing cutaneous manifestations. On the other hand, in experimental studies UV radiation has a number of immunomodulatory effects and stimulates vitamin D synthesis. Our objective was to examine the mucocutaneous manifestations of SLE patients from the GLADEL cohort in relation to latitude and solar radiation of the place where they lived along Central and South America by performing an ecological study.
Materials and methods GLADEL patients were categorised according to latitude and solar radiation (insolation on horizontal surface) of the Rheumatology Centre where they were recruited, ascertained between the period of cohort follow up (1995–2004); this was obtained using NASA Surface meteorology and Solar Energy estimator (https://eosweb.larc.nasa.gov/cgi-bin/sse/interann.cgi?email=skip@larc.nasa.gov). Alopecia, photosensitivity, malar rash, discoid lesions, oral ulcers and subacute cutaneous lupus at cohort entry and during follow up were examined in multivariate models in relation to the average daily solar radiation of the city of residence (as a continuous variable) and other possible confounders.
Results The GLADEL cohort included 1480 lupus patients, with a disease duration < 2 years at entry, 89.9 % female (CI: 88–91), mean age at diagnosis 29.5 (SD 12.3), median follow up 52 months (IQR 24–70), from 34 centres of 22 cities of 9 countries in Latin America. Latitudes of these centres varied between −38° S (Mar del Plata, Argentina) and 25.7° N (Monterrey, Mexico) and mean daily solar radiation varied between 4.44 Kwh/m2/day (Porto Alegre, Brazil) and 6.08 Kwh/m2/day (Recife, Brazil). When entering the cohort, 1191 patients (80.47%) had one or more of the cutaneous manifestations mentioned above and 434 patients (29.31%) developed new skin involvement during follow?up.
In logistic regression analysis after adjusting for age, gender, ethnic group, urban residence, latitude, antimalarial use and autoantibodies, living in a city with higher daily solar radiation (examined at 1 Kwh/m²/day increments) was not associated to any of the cutaneous manifestations at disease onset or during follow up (Table 1).
Conclusions In the GLADEL cohort, the average solar radiation of the city of residence was not associated with an increased risk of developing cutaneous manifestations.
Acknowledgements On behalf of GLADEL group
