Foods containing a widely used additive may increase the growth of lung cancers or cause new tumors to develop, new research suggests.

Tumors were more plentiful in mice with lung cancer fed a diet containing 0.5 to 1 percent inorganic phosphates (equivalent to the 40 mg. that humans on average consume daily) for a month according to a study in next month's American Journal of Respiratory and Critical Care Medicine. The tumors' mass increased by 14 percent in the mice fed the most phosphates.

Inorganic phosphates are chemicals added to a variety of processed foods including cheese, meat, beverages and bakery products to increase water retention and improve their texture. The additives may disrupt the regulation of cell growth in the lungs, causing tumors to develop, says Myung-Haing Cho, a veterinarian at Seoul National University who co-authored the study.

But Stephen Spiro, deputy chairman of the British Lung Foundation, is skeptical there's a human link. "Whilst this may be a relevant observation, it has never been assessed in man," he told BBC News, "and any recent increase in high phosphate ingestion due to excessive phosphates in processed foodstuffs would be likely to take many years before they could affect tumor development in humans."

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