Their tests in mice suggest the additives - found in many soft drinks, baked goods and processed meats and cheese - may also help tumours develop in the first place.

'Our study indicates that increased intake of inorganic phosphates strongly stimulates lung cancer development in mice,' Professor Myung Haing Cho of Seoul National University, who led the study, said in a statement.

A diet high in phosphates 'significantly increased the lung surface tumour lesions as well as the size', Prof Cho's team wrote in their study.

Prof Cho said the research suggests that cutting back on inorganic phosphates 'may be critical for lung cancer treatment as well as prevention'. Phosphates are critical to human nutrition and can be used in compounds that enrich calcium and iron content and prevent food from drying out.

But Prof Cho said it is possible that some people get too much.

'In the 1990s, phosphorous-containing food additives contributed an estimated 470mg per day to the average daily adult diet,' Prof Cho said.

Now, he said, people can get up to 1,000mg a day.

Writing in the American Journal of Respiratory and Critical Care Medicine, Prof Cho and colleagues said they studied mice bred to develop lung cancer. For a month, half got diets equivalent to a human diet high in phosphates and the other half got a moderate dose.

The bred mice do not develop cancer in the same way as humans do and the researchers stressed their study does not show that the food additives contribute to cancer in people.

Instead, it points to questions for human cancer researchers to study.

Lung cancer is by far the most common cancer killer around the world, killing 1.2 million people a year. Smoking is the most common cause but a majority of smokers do not develop lung cancer, so scientists are looking for other factors that may help tumors develop and spread.

Prof Cho's team found phosphate-rich diets affected the Akt gene, known to be involved in lung cancer, and suppressed another gene that can help slow cancer's development. -- REUTERS