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P325. Low sun exposure is associated with an increased risk of Crohn's disease in the E3N cohort study

P. Jantchou1,2, F. Clavel-Chapelon2, F. Carbonnel2,3, M. Boutron-Ruault2

1CHU Besançon, Besançon, France; 2INSERM, UMRS 1018, Team 9, Centre for Research in Epidemiology and Population Health, Université Paris Sud, Institut Gustave Roussy, Villejuif, France; 3Gastroenterology Unit, Bicêtre University Hospital, Le Kremlin Bicêtre, France

Introduction: A North–South gradient of inflammatory bowel diseases (IBD) incidence have been described in Europe, USA, Scotland and France. The aim of this work was to analyse the relationship between incident Crohn's disease (CD) or Ulcerative cases (UC) and the level of sun exposuer.

Patients and Methods: The cohort (E3N) consists of women living in France, aged 40–65 years and free of major disease at inclusion. Among the 91870 women included in the study, we identified 123 incident cases of IBD (45 CD, 71 UC and 7 indeterminate colitis).

The surface UV radiation intensity was obtained by combining modeling and satellite data from Meteosat®, the European meteorological satellite. Data were available for each “department” from January 1984 to August 2003. The mean sun exposure for each women was calculated for two different periods: for winter period and summer period by summing the monthly exposure from January 1984 to December 1989 for each of these periods.

Relationship between sun exposure and risk of incident IBD was estimated using the Cox proportional hazards models.

Results: In this cohort, a high sun exposure was associated with a decreased risk of CD: (Hazard Ratio (HR) for the third compared to the first tertile 0.46; 95% confident interval (CI): 0.22–0.98; P trend = 0.03) but not of UC (Table 1).

Adjusting for physical activity, body mass index, tobacco smoking, menopause hormone therapy, or socio-economic status did not substantially modify the association between sun exposure and IBD.

Conclusion: In this prospective cohort, we found an association between low sunlight exposure and increased incidence of CD. Wheteher this association is causal remains to be elucidated.

Table 1. Relation between sun exposure and risk of IBD in the E3N cohort study
VariableFirst tertileSecond TertileThird tertileP of trend
Ulcerative ColitisSun exposure in winter10.88 (0.49–1.57)1.02 (0.59–1.78)0.93
 Sun exposure in summer11.03 (0.58–1.81)1.00 (0.56–1.79)1.00
Crohn's diseaseSun exposure in winter10.70 (0.36–1.37)0.49 (0.23–1.05)0.06
 Sun exposure in summer10.56 (0.28–1.11)0.46 (0.22–0.98)0.03