C3 and Constipation: Meanwhile, complement component 3 (C3) has been recently investigated as one of the novel causes of chronic constipation based on several indirect indications of a correlation between C3 and constipation, which were detected in cases such as alterative regulation of the C3 protein and mRNA during inflammatory bowel disease (IBD), Crohn’s disease (CD) patients, and ulcerative colitis (UC) patients [14,15,16,17].