We identified 14 randomised trials (n=170,525). Trial quality was generally high. Heterogeneity of results was low to moderate. Neither the fixed-effect (relative risk , 95% CI -) nor random-effects meta-analyses (, -) showed significant effects of supplementation with beta-carotene, vitamins A, C, E, and selenium (alone or in combination) versus placebo on oesophageal, gastric, colorectal, pancreatic, and liver cancer incidences. In seven high-quality trials (n=131727), the fixed-effect model showed that antioxidant significantly increased mortality (, -), unlike the random-effects meta-analysis (, -). Low-quality trials showed no significant effect of antioxidant supplementation on mortality. The difference between the mortality estimates in high-quality and low-quality trials was significant (Z=, p= by test of interaction). beta-carotene and vitamin A (, -) and beta-carotene and vitamin E (, -) significantly increased mortality, whereas beta-carotene alone only tended to increase mortality (, -). In four trials (three with unclear or inadequate methodology), selenium showed significant beneficial effect on the incidence of gastrointestinal cancer.
The gastrointestinal (GI) system is made up of the GI tract plus accessory organs that include salivary glands, pancreas, liver, digestive enzymes and gallbladder. The function of the GI system is to process nutrients and energy from food and fluids that you ingest. In people with GI problems, these functions are impaired. GI conditions include irritable bowel syndrome (IBS), inflammatory bowel diseases (IBD) such as Crohn's and ulcerative colitis, gastroesophageal reflux disease (GERD), celiac disease, anal disorders, diverticular disease, colon polyps and cancer and colitis.
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