New research in an animal model suggests that a diet high in inorganic phosphates -- found in a variety of processed foods, including meats, cheeses, beverages and bakery products -- might speed the growth of lung-cancer tumors and may even contribute to the development of those tumors in individuals predisposed to the disease.
The study also suggests that dietary regulation of inorganic phosphates may play an important role in lung-cancer treatment. The research, using a mouse model, was conducted by Myung-Haing Cho, D.V.M., Ph.D., and his colleagues at Seoul National University, appears in a recent issue of the American Journal of Respiratory and Critical-Care Medicine, published by the American Thoracic Society.
"Our study indicates that increased intake of inorganic phosphates strongly stimulates lung-cancer development in mice, and suggests that dietary regulation of inorganic phosphates may be critical for lung-cancer treatment as well as prevention," said Cho.
Lung cancer is the No. 1 cause of cancer deaths in the world, and is also the most frequently diagnosed solid tumor. Non-small-cell lung cancer constitutes more than 75 percent of lung cancers, and has an average overall 35-year survival rate of 14 percent.
Earlier studies have indicated that approximately 90 percent of NSCLC cases were associated with activation of certain signaling pathways in lung tissue. This study revealed that high levels of inorganic phosphates can stimulate those same pathways.
"Lung cancer is a disease of uncontrolled cell proliferation in lung tissue, and disruption of signaling pathways in those tissues can confer a normal cell with malignant properties," explained Cho.
"Deregulation of only a small set of pathways can confer a normal cell with malignant properties, and these pathways are regulated in response to nutrient availability and, consequently, cell proliferation and growth.
"Phosphate is an essential nutrient to living organisms, and can activate some signals," added Cho. "This study demonstrates that high intake of inorganic phosphates may strongly stimulate lung-cancer development by altering those [signaling] pathways."
In the study, lung-cancer model mice were observed for four weeks and randomly assigned to receive a diet of either .5 percent or 1 percent phosphate, a range roughly equivalent to modern human diets. At the end of the four-week period, the lung tissue was analyzed to determine the effects of the inorganic phosphates on tumors.
"Our results clearly demonstrated that the diet higher in inorganic phosphates caused an increase in the size of the tumors and stimulated growth of the tumors," said Cho.
He noted that while a moderate level of phosphate plays an essential role in living organisms, the rapidly increasing use of phosphates as a food additive has resulted in significantly higher levels in average daily diets. Phosphates are added to many food products to increase water retention and improve food texture.
Explained Cho: "In the 1990s, phosphorous-containing food additives contributed an estimated 470 mg per day to the average daily adult diet. However, phosphates are currently being added much more frequently to a large number of processed foods, including meats, cheeses, beverages and bakery products.
"As a result, depending on individual food choices, phosphorous intake could be increased by as much as 1,000 mg per day."
Cho ended by saying that future studies will help refine what constitutes a "safe" level of dietary inorganic phosphate, with recommendations that will be easily achievable in the average population.