High doses of vitamin C inhibit the bacteria that causes ulcers, Helicobacter pylori growth in culture. Vitamin C's inhibitory effects seem to be specific to H. pylori and a close cousin, Campylobacter jejuni, but vitamin C had no effect on various gram-negative bacteria.
Epidemiologic evidence and clinical experiments suggest that vitamin C may exert protective effects against the development of gastric cancer. It is estimated that 40% of the US population consumes vitamin supplements, which may account for the lower incidence of gastric cancer in the US compared with Japan, where gastric cancer is the most common cancer. H. pylori is also far less prevalent in the US compared with Japan.