Although salt is a necessity, U.S. consumers are unlikely ever to be deficient in salt (sodium). Our diets are heavily loaded with salt, the majority of which is derived from processed food, fast food, and restaurant meals. Increasing salt consumption is correlated with higher blood pressure in the majority of people, so that high salt consumption serves to promote heart disease and stroke. Salt consumption is also suspected of contributing to insulin resistance and metabolic syndrome, which themselves may be associated with increased risk of breast cancer. High salt consumption has been found to be associated with increased risk of pancreatic cancer. Consumption of highly salted foods (including fermented soybean products, pickled vegetables, preserved salted vegetables, and salted fish) has also been found to be associated with increased risks of ovarian and prostate cancer in China. Consumption of salted fish has been shown in several studies to increase the risks of nasopharyngeal and colorectal cancers, as well as stomach cancer. One South American study found the risk of esophageal cancer to increase with increasing consumption of salt.
Breast cancer-related effects of consuming salt
The relationship between salt and cancer is related to two types of salt intake: high overall intake and high intake of very salty foods. The relatively high overall level of salt in the average U.S. diet contributes to cancer risk indirectly by promoting metabolic syndrome and reducing the potassium/sodium ratio in the diet, both of which are thought to increase the risks of various cancers.
The second type of cancer-promoting salt intake occurs when people consume highly salted specialty foods, condiments and snacks. These foods act directly on the digestive track and have been shown in numerous studies to cause stomach (gastric) cancer. Implicated foods include dried and salted fish and seafood, fermented/pickled vegetables, fish sauce, kimchi, salted preserved vegetables, salted and fermented soybean paste, salted fish preserves, salted fish roe, salted meat, salted shrimp paste, salty snacks, and salty soups. Many of the foods listed above are Asian; since the rate of stomach cancer is relatively high in Asia, there has been great interest in investigating the causes. Note however, that European and South American studies also have found associations between heavily salted foods and stomach cancer.
A 2018 study reported that hormone receptor positive (ER+/PR+) and triple negative (ER-/PR-/HER2-) breast cancer cells exerted higher tumorigenicity when exposed to high levels of salt. The same study found that high salt induced resistance to the chemotherapy drug Taxol in breast cancer cells.
There is some evidence that breast cancer survivors are at increased risk of developing stomach cancer and lobular breast cancer survivors in particular are vulnerable to gastric metastases.
Sodium nitrite and related compounds are routinely added to processed meat and some other salty foods to preserve their freshness and coloring. Sodium nitrite has been shown to react with chemicals in the stomach to produce nitrosamines, which are known to be cancer-promoting. However, the cancer-related effects of salt consumption are not dependent on the presence of sodium nitrite; this carcinogen simply worsens the cancer profile of salty foods that contain it.
Iodine deficiency is a major cause of preventable mental retardation found worldwide. Iodized salt is designed to prevent this deficiency.
Note that while we are continually searching for new evidence specifically concerning this food, there is not much interest in it among breast cancer researchers, so few studies are available.