High powered radio waves from mobile phone base stations appear to have no adverse effects on human tissue, according to research sponsored by Japanese mobile phone operators.

Experiments involved researchers blasting samples of living cells from brain, skin and lung tissue with radio waves up to 10 times stronger than legal safety limits for mobile base station transmitters.

The researchers claimed that no adverse effects were detectable even after as much as 96 hours of exposure.

The research was carried out by the Mitsubishi Chemical Safety Institute (MCSI) on behalf of Japan's three largest mobile phone operators, SoftBank Mobile Corp, NTT DoCoMo and KDDI Corp. 

MCSI is a member of the giant Mitsubishi group of companies, members of which provide a wide variety of products and services including mobile phones.

The Japanese mobile phone firms have not yet published full details of the research findings.

However, according to an interim research paper released last year, technicians conducting the research looked for signs of genetic damage. Tests of 44,000 cell samples had revealed "no consistent significant effect on gene expression".

The researchers based their findings partly on the absence of excess heat-shock proteins in the cells that they had bombarded with radio waves.

Heat-shock proteins are manufactured in cells when they are under stress, as part of a damage control process.

They also looked for signs that badly damaged cells were attempting to dispose of themselves by a process of 'apoptosis', or cellular suicide.

The researchers tested radio signals of the frequency and transmission pattern emitted by a 2GHz-band Wideband-Code Division Multiple Access base station, according to a statement published by NTT DoCoMo.

Research into the health effects of mobile phone use has produced a wide range of results.

A recent study by the Finnish Radiation and Nuclear Safety Authority found that long-term mobile phone use could slightly increase the risk of brain tumours developing on the side of the head where the phone is held.

This effect was only observed in cases where the user had owned a mobile phone for more than 10 years, the researchers said.