EXPOSURE to mobile phones could trigger cancer in the heart, brain and adrenal gland, scientists have warned.

There is now “clear evidence” that exposure to radiation from mobile phones causes the disease, a landmark new study from the National Institutes of Health (NIH) found.

Although the tests were done on rodents at radiation levels much higher than humans are currently exposed, to there was a clear link with male rats.

For female rats, and mice of both sexes, the evidence was less clear as to whether cancers observed were associated with signal exposure.

Senior scientist Dr John Bucher at the National Toxicology Programme in Durham, North Carolina said: “The exposures used in the studies cannot be compared directly to the exposure that humans experience when using a cell phone.

“In our studies, rats and mice received radio frequency radiation across their whole bodies.

“By contrast, people are mostly exposed in specific local tissues close to where they hold the phone.

“In addition, the exposure levels and durations in our studies were greater than what people experience.”

The finding was the result of a $30m (£23m)10 year study to assess the health effects in animals exposed to radio frequency radiation from 2G and 3G phones.

Dr Bucher added: “Cell phones utilise a specific type of radio waves, or radio frequency radiation (RFR), to transmit between the devices and the network.

“Exposure of people to RFR occurs primarily through use of cell phones and other wireless devices.

“We studied the effects of nearly lifetime exposures to two different types, or modulations, of RFR used in cellular telephone networks in the United States in male and female rats and mice to identify potential toxicity or cancer-related hazards.

“When the current studies were being designed, 2G technology was the industry standard, and 3G technologies were under development.

“While newer technologies have continued to evolve, it is important to note that these technologies have not completely replaced the older technologies.

“In fact, today's phones are very complex in that they contain several antennas, for Wi-Fi, GPS, 2G/3G bands.

“The results of these studies remain relevant to current exposures, although the power levels of the exposures were much higher than typical patterns of human use.”

The lowest exposure level to radiation used in the studies was equal to the maximum amount phone users can be exposed to – levels that rarely occur with regular phone use.

The highest amount of radiation was four times higher than what’s permitted.

“We believe that the link between radio frequency radiation and tumours in male rats is real, and the external experts agreed,” Dr Bucher said.

“A major strength of our studies is that we were able to control exactly how much radio frequency radiation the animals received - something that's not possible when studying human cell phone use, which has often relied on questionnaires.”

Exposure to RFR began in the womb for rats and at five to six weeks old for mice, and continued for up to two years, or most of their natural lifetime.

The RFR exposure was intermittent, 10 minutes on and 10 minutes off, for about nine hours each day.

Future studies will focus on developing measurable physical indicators, or biomarkers, of potential effects from RFR.

These may include changes in metrics like DNA damage in exposed tissues, which can be detected much sooner than cancer.