Causes

While the cause of ulcerative colitis is unknown, several, possibly interrelated, causes have been suggested.

Genetic factors

A genetic component to the etiology of ulcerative colitis can be hypothesized based on the following:

• Aggregation of ulcerative colitis in families.
• Twin concordance studies, although the evidence is less than for Crohn's disease
• Ethnic differences in incidence
• Genetic markers and linkages

Chromosome band 1p36 is linked to inflammatory bowel disease.

Environmental factors

Many hypotheses have been raised for environmental contributants to the pathogenesis of ulcerative colitis. They include the following:

• Diet: as the colon is exposed to many different dietary substances which may encourage inflammation, dietary factors have been hypothesized to play a role in the pathogenesis of both ulcerative colitis and Crohn's disease. There have been few studies to investigate such an association, but one study showed no association of refined sugar on the prevalence of ulcerative colitis.
• Smoking: unlike Crohn's disease, ulcerative colitis has a lesser prevalence in smokers than non-smokers.
• Breastfeeding: There have been conflicting reports of the protection of breastfeeding in the development of inflammatory bowel disease. One Italian study showed a potential protective effect.
• Other childhood exposures, or infections

Autoimmune disease?

Some sources list ulcerative colitis as an auto-immune disease, a disease in which the immune system malfunctions, attacking some part of the body.

As discussed above, ulcerative colitis is a systemic disease that affects many areas of the body outside the digestive system. Surgical removal of the large intestine often cures the disease, including the manifestations outside the digestive system. This suggests that the cause of the disease is in the colon itself, and not in the immune system or some other part of the body.

Alternative theories

The Radical Induction Theory of Ulcerative Colitis proposes that the initial cause of ulcerative colitis is a malfunction in the patient's metabolism that results in excess levels of oxygen free radicals related hydrogen peroxide in the cells of the intestine. The author also reports colitis subsequent to administration of vitamin B6 and iron as dietary supplements.

Levels of sulfate-reducing bacteria tend to be higher in persons with ulcerative colitis. This could mean that there are higher levels of hydrogen sulfide in the intestine. An alternative theory suggests that the symptoms of the disease may be caused by toxic effects of the hydrogen sulfide on the cells lining the intestine.