Stomach cancer is the #3 cause of cancer deaths worldwide. However, most of these deaths are occurring in developing countries, with China experiencing close to 300,000 deaths from stomach cancer each year. Population studies have shown a higher average salt intake in in population correlates with greater risk of death from stomach cancer. While case-control studies have shown similar results, indicating that people within a population who consume the most salt generally have a higher risk of developing or dying from stomach cancer, the overall results from cohort studies are not totally consistent. That said, there does appear to be an association with the intake of salt-preserved foods and stomach cancer. There is a greater than 10-fold increase in stomach cancer incidence and mortality between populations consuming the lowest and highest amounts of dietary salt. Additionally, this difference appears much more pronounced in developing countries (1).
In the USA, stomach cancer prevalence and deaths have declined markedly from the top cancer killer in the early part of the 20th century to a far less common cause of cancer death today. This decline was largely not the result of improved medical treatment of stomach cancer but rather occurred along with cleaner water supply, the growing use of refrigeration with less reliance on the smoking, salting, and pickling of foods such as fish and meats for preservation. Another factor contributing to the decline in stomach cancer was likely the growing use of antibiotics after World War II. Indeed, the growing use of antibiotics aimed at eliminating Helicobacter pylori (H. pylori) infection starting in the 1980s, when it was discovered that H. pylori infections were the main cause of ulcers, has no doubt also helped reduce stomach cancer mortality as well. There is now growing evidence that H. pylori infections as well as diet play a prominent role in promoting stomach cancer.
This year in the USA, stomach cancer will be diagnosed in an estimated 27,510 people (17,230 men and 10,280 women) in the USA. It is also estimated that there will be 11,140 deaths (6,800 men and 4,340 women) that result from stomach cancer (2).
Salt + H. pylori Promote Progression of Stomach Cancer
Stomach cancer appears to result from chronic inflammation that leads to precancerous changes in the stomach’s epithelial cells. First one develops atrophic gastritis and other dysplastic changes in the stomach’s normal lining. These precancerous lesions eventually lead to the development of stomach cancer. Dr. Susan Thapa at the University of Arkansas and colleagues conducted a study to examine the effect of dietary salt intake on progression of these precancerous stomach lesions. Data was collected from a prospective cohort study conducted among participants both with and without H. pylori infection. Estimations of salt intake were collected using urinary sodium/creatinine ratios from spot urine samples, self-reported frequency, and the amount of salt added to food while eating. The researchers observed a weak but not significant association between salt intake and the progression in the gastric precancerous lesion to malignancy. However, when looking only at those with H. pylori infections, a higher salt intake was correlated with the progression from precancerous to malignant lesion. This effect was strongest among those who remained infected with Helicobacter pylori over the twelve years.
Why Is Salt Mostly a Problem in People with H. pylori?
While dietary salt may damage the stomach lining and contribute to the development of precancerous atrophic gastritis, it appears to do so in large part in those infected with H. pylori. Indeed, there is evidence that H. pylori infections mutate to a more virulent strain when exposed frequently to a high salt diet. Especially in people with H. pylori infections, the dietary factors most commonly linked to much greater risk of developing stomach cancer would be a diet are rich in salted, pickled and smoked foods, and especially a diet high in smoked fish and high in meat content, especially processed meats. A higher intake of whole fruits and vegetables appears to reduce the risk of H. pylori induced stomach cancer (3). In developing countries, many people become infected with H. pylori from untreated water. In modern societies, H. pylori is largely an infectious disease transferred from person to person by kissing or sharing a toothbrush. Parents can pass H. pylori to their kids by sharing food. Treatment of H. pylori infections with antibiotics can eliminate these infections and has been shown to dramatically reduce the risk of developing ulcers. Most reoccurring ulcers and chronic gastritis are now believed to be due largely to this still all-too-common chronic bacterial infection. The fact that diet and H. pylori apparently work synchronously to promote precancerous atrophic gastritis and eventually malignant stomach cancer should allow for further progress at reducing stomach cancer deaths in the USA and dramatically reducing such deaths in developing countries.
Bottom Line: Stomach cancer is killing close to a million people worldwide each year. There is now sufficent knowledge that should allow most stomach cancer cases to be eliminated. Adopting a healthier diet lower in highly salted smoked, pickled, and processed meats and fish and more fresh fruits and vegetables could dramatically reduce the risk of people with precancerous atrophic gastritis from progressing to a malignant stomach cancer. People with a history of ulcers or chronic gastritis should be tested for H. pylori infections and, if it's present, treating these infections with antibiotics should also help reduce the risk of developing a malignant stomach cancer.
By James J. Kenney, PhD, FACN
- Parkin DM. International variation. Oncogene. 2004;23:6329–40 DOI:10.1038/sj.onc.1207726.
Stephanie Ronco has been editing for Food and Health Communications since 2011. She graduated from Colorado College magna cum laude with distinction in Comparative Literature. She was elected a member of Phi Beta Kappa in 2008.