BEIJING, Sept. 30 (Xinhuanet) -- Tobacco companies concealed the knowledge of radioactive substance in cigarettes from public for over four decades, a new study revealed.

The revelation was made by a research team from the University of California, Los Angeles, published on Thursday in the online edition of the U.S. medical journal Nicotine and Tobacco Research.

The researchers analyzed 27 timeworn documents and discovered that tobacco companies had knew the existence of polonium-210, a hazardous radioactive substance, in the tobacco since 1959.

The companies studied polonium-210 throughout the 1960s, and concealed their findings about the carcinogenic potential of the radioactive substance.

Hrayr Karagueuzian, the study's lead author, said the tobacco companies' deception surprised him.

According to the revelation, the companies had knew the "cancerous growths" in the lungs of smokers, and even calculated how much radiation a regular smoker would inhale over 20 years.

Karagueuzian and his team conducted again the study recorded in the tobacco documents and found that the radiation in cigarettes would cause up to 138 deaths for every 1,000 smokers over a period of 25 years.

However, tobacco manufacturer denied that they had concealed the facts from the public.

David Sutton, spokesman of Philip Morris, the largest U.S. tobacco company, said the polonium-210 was a "naturally occurring element in the air" and had been widely discussed by the public health community for years.