Marc Sorenson, EdD
IBD consists of two primary diseases, ulcerative colitis (UC) and Crohn’s disease (CD). UC is a chronic inflammatory condition characterized by relapsing and remitting episodes of inflammation limited to the mucosal layer of the colon.  Crohn’s however, can involve any part of the gastrointestinal tract from the mouth to the anus but most commonly affects the small intestine or the colon or both. The most common symptoms of IBD are abdominal pain, weight loss, fever, rectal bleeding, skin and eye irritations and diarrhea.
In a 12-year year investigation of hundreds of thousands of IBD patients, measuring both UC and CD, hospitalizations and prolonged hospitalizations for both diseases were higher among those who had low sunlight exposure compared to those with very high sunlight exposure. The same relationship was shown between sunlight, bowel surgeries and deaths; more surgeries were needed for those patients who experienced the lowest sunlight exposure compared to those who had the highest sunlight exposure, and more deaths occurred among those with low exposure.
An interesting side note to this investigation was that a large number of non-IBD patients were also analyzed for sunlight exposure amounts. As with the IBD patients, low sunlight exposure was associated with prolonged hospitalizations and more deaths when compared with high exposure.
French research has shown that high residential sun exposure is associated with a low risk of CD, but not UC. Women who were in the highest third of sunlight exposure had only half the risk of CD compared to those in the lowest third, but UC was increased 21% by high sunlight exposure. This study was the only one I have seen—other than studies on non-melanoma skin cancer—that indicated a positive association of sunlight exposure with disease risk. None of the other studies mentioned here showed that relationship with UC. Another interesting side note to this research was that vitamin D intake was not associated with decreased risk of CD.
It has also been shown that in both Europe and the US, there is a north-south gradient for IBD, meaning that the risk of developing IBD is significantly lower for the southern latitudes (where sunlight exposure is greater). And finally, another French study has demonstrated that low sunlight exposure is associated with an increased incidence of Crohn’s disease.
So for a healthy gut, sunlight exposure plays a vital role.
 Mark A Peppercorn, Adam S Cheifetz, Paul Rutgeerts, Shilpa Grover. Definition, epidemiology, and risk factors in inflammatory bowel disease. Uptodate http://www.uptodate.com/contents/definition-epidemiology-and-risk-factors-in-inflammatory-bowel-disease. Accessed July 1, 2015.
 Web MD http://www.webmd.com/ibd-crohns-disease/crohns-disease/inflammatory-bowel-syndrome. Accessed July 1, 2015.
 Limketkai BN1, Bayless TM, Brant SR, Hutfless SM. Lower regional and temporal ultraviolet exposure is associated with increased rates and severity of inflammatory bowel disease hospitalization. Aliment Pharmacol Ther. 2014 Sep;40(5):508-17.
 Jantchou P1, Clavel-Chapelon F, Racine A, Kvaskoff M, Carbonnel F, Boutron-Ruault MC. High residential sun exposure is associated with a low risk of incident Crohn’s disease in the prospective E3N cohort. Inflamm Bowel Dis. 2014 Jan;20(1):75-81.
 Schultz M1, Butt AG. Is the north to south gradient in inflammatory bowel disease a global phenomenon? Expert Rev Gastroenterol Hepatol. 2012 Aug;6(4):445-7.
 Nerich V1, Jantchou P, Boutron-Ruault MC, Monnet E, Weill A, Vanbockstael V, Auleley GR, Balaire C, Dubost P, Rican S, Allemand H, Carbonnel F. Low exposure to sunlight is a risk factor for Crohn’s disease. Aliment Pharmacol Ther. 2011 Apr;33(8):940-5.