Evaluation of the aetiological role of dietary salt exposure in gastric and other cancers in humans.

The findings in laboratory and epidemiological studies relevant to the assessment of salt for carcinogenic potential are reviewed. Associations between the high consumption of certain highly salted foodstuffs, particularly in some oriental countries, and increased risk of cancer of the stomach do not incriminate salt per se. Some highly spiced foods contain potent genotoxic carcinogens, irrespective of whether they also contain salt. There is evidence in laboratory animals that high concentrations of salt may increase the incidence of gastric cancer caused by such carcinogens. This may well be attributable to a marked and sustained regenerative response in the gastric mucosa of laboratory animals chronically exposed to the cytotoxicity of hyperosmolar concentrations of salt, such a mitogenic response favouring the progression towards neoplasia. However, there is no laboratory evidence whatsoever to indicate that salt per se is a carcinogen for any site in the body; neither is there any reliable epidemiological evidence to indicate that dietary salt affects the incidence of gastric or other cancers. A particular problem in the interpretation of epidemiological studies is that the consumption of diets containing highly salted, spicy foods is often associated with low intakes of fruit and green vegetables, which contain cancer-protective antioxidants. In Western countries the incidence of cancer of the stomach has been falling for some 50 years. The consensus view is that this fall is attributable to improved food hygiene and increasingly available facilities for refrigeration. There are no grounds for supposing that the fall is attributable to a decreasing intake of salt. A high dietary salt intake does not necessarily entail exposure to salt in concentrations high enough to damage the gastric mucosa. The typical Western diet would not be expected to provide such high salt concentrations. It is concluded that there are no grounds for believing that a reduction in the average daily salt intake in the Western diet would have any effect on the risk of developing any form of cancer.