While previous studies show results of animal trials cannot always be replicated in humans, the researchers say dietary restrictions of the additive may be critical for lung cancer treatment as well as prevention.

The Seoul National University study suggests a diet high in inorganic phosphates could speed growth of cancerous tumours and contribute to the development of tumours in those predisposed to the disease.

Inorganic phosphates are found in a variety of processed foods, including meats, cheeses, beverages and bakery products. They are added to increase water retention and improve food texture.

Moderate levels of phosphate play an essential role in living organisms, but the rapidly increasing use of the chemical as a food additive has resulted in significantly higher levels in average daily diets.

The Seoul study appears in the American Journal of Respiratory and Critical Care Medicine.

Lung cancer is the number-one cause of cancer deaths in the world and is also the most frequently diagnosed solid tumor.

Earlier studies showed that about 90% of the most common form of lung cancer cases were associated with a disruption of signalling pathways in lung tissue that can cause normal cells to become malignant. This study revealed that high levels of inorganic phosphates may disrupt those same pathways, said study co-author and veterinary medicine professor Myung-Haing Cho.

He and his team used mice genetically engineered to be susceptible to lung cancer. They randomly assigned the mice to receive a diet of either 0.5 or 1.0% phosphate, a range roughly equivalent to modern human diets. After four weeks, they analyzed the mice's lung tissue.

"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," Cho said in a release.

Cho said future studies will help refine what constitutes a "safe" level of dietary inorganic phosphate.

From the January 5, 2009, Prepared Foods e-Flash