Gastric cancer is linked to infection by helicobacter pylori, the bacteria that is known to be a common cause of gastric ulcers. Infection with helicobacter pylori is associated with low gastric concentrations of vitamin C although the exact relationship between these variables in not fully understood. Studies have shown that eradication of helicobacter pylori infections can normalise the concentration of vitamin C in the gastric juice, and this is thought to be due to an infection related increase in gastric acid pH which impairs the secretion of vitamin C from the gastric mucosa. When the infection clears vitamin C secretion then normalises. Some evidence suggests that populations that are at high risk of gastric cancer may have circulating levels of vitamin C that are lower than those populations that are at low risk. Some populations in China for example are known to have a particularly high incidence of gastric cancer, and researchers are interested in nutritional factors that might affect this risk.
For example, in one study, researchers1 investigated the association between the risk of gastric cancer and circulating vitamin C concentrations in a population of Chinese men and women living in the Linxian province of China. In particular, the researchers assessed the pre-diagnostic vitamin C plasma concentrations of nearly 30,000 individuals with the incidence of gastric cancer. The results of the study showed that a 20 μmol/L increase in plasma vitamin C was associated with a 14 % reduction in the risk of of gastric cancer. Those individuals with a plasma vitamin C concentration above 28 μmol/L (considered normal levels) had a 27 % reduction in gastric cancer risk compared to those individuals with a plasma vitamin C concentration below 28 μmol/L. A meta-analysis of existing data showed that those with the highest plasma vitamin C concentrations had a 31 % lower risk of gastric cancer than those with the lowest levels. Plasma vitamin C is therefore inversely associated with the risk of gastric cancer.
Dr Robert Barrington’s Comments: A number of biological roles have been suggested for vitamin C in the prevention of gastric cancer. Vitamin C is a water soluble antioxidant and may protect gastrointestinal cells from DNA damage. As vitamin C secretion falls with helicobacter pylori infection, is is possible that this results in an increase risk of carcinogenesis in the gut. Higher plasma levels of vitamin C may maintain vitamin C secretion thus preventing the formation of a carcinogenic environment. Of course as all vitamin C is of dietary origin, and ingested vitamin C has to pass through the gut before absorption. Higher intakes of vitamin C will supplement any secreted vitamin C from the gastric mucosa prior to absorption. The higher plasma levels of vitamin C seen in those with the lowest risk of gastric cancer could therefore be a marker for a large amount of vitamin C passing through the gut. As vitamin C inhibits the growth of helicobacter pylori, this may explain the association.
RdB
