Can orange juice prevent ulcers? In a study of 7,000 Americans, researchers found that the lower the level of vitamin C in a person's blood, the more likely that he or she will be infected by the bacteria Helicobacter pylori, which is linked to ulcers and stomach cancer. The researchers do not yet know whether a low vitamin level is the cause or the effect of the H. pylori infection. But even if it is the latter, the study's authors believe it prudent for people who test positive for the bug to increase their vitamin C intake.