Inflammatory bowl diseaseExposure to sunlight

Two studies reported higher rates of IBD and higher latitudes compared to lower latitudes: Europe1 and France2 3, and one study also reported a latitudinal gradient for Crohn's disease (CD) in Scotland4

The geographical variation for CD in France is similar to that for breast cancer5 6 and other cancers5, which has been linked to solar UVB doses and vitamin D production. However, the geographical variation of UC in France does not show a similar latitudinal gradient.

In the United States, rates for CD and Ulcerative colitis (UC) are highest in the northeast7 8 9In the United States, summertime solar UVB doses are highest in the southwest, lowest in the northeast10 (see map).

The reasons include that the surface elevation is generally higher in the west and the ozone layer is thinner as the westerly winds push the tropopause higher as the air masses prepare to cross the Rocky Mountains. Wintertime solar UVB doses vary with latitude with no asymmetry11.

The data both prevalence and mortality rates by state for CD, UC, and Clostridium difficile colitis in the United States9 [Sonnenberg, 2010], were analyzed in an ecological study using summertime UVB, wintertime UVB, smoking, and obesity. For CD, summertime UVB (inverse association or risk reduction) and smoking (risk) were significantly correlated. For UC, UVB was significantly inversely correlated, but not as strong as for DC. Smoking was correlated with C. difficile colitis.

A study from India reported lower serum 25(OH)D levels in those with CD with lower sun exposure12.

Page last edited: 06 May 2011


  1. Shivananda, S. Lennard-Jones, J. Logan, R. Fear, N. Price, A. Carpenter, L. van Blankenstein, M. Incidence of inflammatory bowel disease across Europe: is there a difference between north and south? Results of the European Collaborative Study on Inflammatory Bowel Disease (EC-IBD). Gut. 1996 Nov; 39 (5): 690-7.
  2. Nerich, V. Monnet, E. Etienne, A. Louafi, S. Ramee, C. Rican, S. Weill, A. Vallier, N. Vanbockstael, V. Auleley, G. R. Allemand, H. Carbonnel, F. Geographical variations of inflammatory bowel disease in France: a study based on national health insurance data. Inflamm Bowel Dis. 2006 Mar; 12 (3): 218-26.
  3. Nerich, V. Monnet, E. Weill, A. Vallier, N. Vanbockstael, V. Auleley, G. R. Balaire, C. Dubost, P. Rican, S. Allemand, H. Carbonnel, F. Fine-scale geographic variations of inflammatory bowel disease in France: correlation with socioeconomic and house equipment variables. Inflamm Bowel Dis. 2010 May; 16 (5): 813-21.
  4. Armitage, E. L. Aldhous, M. C. Anderson, N. Drummond, H. E. Riemersma, R. A. Ghosh, S. Satsangi, J. Incidence of juvenile-onset Crohn's disease in Scotland: association with northern latitude and affluence. Gastroenterology. 2004 Oct; 127 (4): 1051-7.
  5. Grant, W. B. An ecological study of cancer incidence and mortality rates in France with respect to latitude, an index for vitamin D production. Deramato-Endocrinology. 2010 April/May/June; 2 (2):
  6. Engel, P. Fagherazzi, G. Mesrine, S. Boutron-Ruault, M. C. Clavel-Chapelon, F. Joint Effects of Dietary Vitamin D and Sun Exposure on Breast Cancer Risk: Results from the French E3N Cohort. Cancer Epidemiol Biomarkers Prev. 2011 Jan; 20 (1): 187-98.
  7. Kappelman, M. D. Rifas-Shiman, S. L. Kleinman, K. Ollendorf, D. Bousvaros, A. Grand, R. J. Finkelstein, J. A. The prevalence and geographic distribution of Crohn's disease and ulcerative colitis in the United States. Clin Gastroenterol Hepatol. 2007 Dec; 5 (12): 1424-9.
  8. Sonnenberg, A. Demographic characteristics of hospitalized IBD patients. Dig Dis Sci. 2009 Nov; 54 (11): 2449-55.
  9. Sonnenberg, A. Similar geographic variations of mortality and hospitalization associated with IBD and Clostridium difficile colitis. Inflamm Bowel Dis. 2010 Mar; 16 (3): 487-93.
  10. Grant, W. B. Garland, C. F. The association of solar ultraviolet B (UVB) with reducing risk of cancer: multifactorial ecologic analysis of geographic variation in age-adjusted cancer mortality rates. Anticancer Res. 2006 Jul-Aug; 26 (4A): 2687-99.
  11. Grant, W. B. Hypothesis--ultraviolet-B irradiance and vitamin D reduce the risk of viral infections and thus their sequelae, including autoimmune diseases and some cancers. Photochem Photobiol. 2008 Mar-Apr; 84 (2): 356-65.
  12. Joseph, A. J. George, B. Pulimood, A. B. Seshadri, M. S. Chacko, A. 25 (OH) vitamin D level in Crohn's disease: association with sun exposure & disease activity. Indian J Med Res. 2009 Aug; 130 (2): 133-7.