Curcumin is a polyphenol. Polyphenol's are the chemicals that give highly coloured plants their colour and tend to be good anti-oxidants.
Back to turmeric. A review by the Cochrane found one study that showed a significant improvement in patients with Ulcerative Colitis (UC) both by clinical and endoscopic measures over a six month period. The important thing to note here is that the patients in both placebo and test were also stable on regular therapy for UC.
Some important things to note:
Interestingly extracts from black pepper (piperine) slows down the metabolism of curcumin by the liver, so maintains blood levels for longer.