One of the largest studies of its kind has found that short-term health effects, such as anxiety, tension and tiredness, are not caused by emissions from phone masts.

The extensive three-year study was conducted at a specially designed laboratory by a team of independent scientists at the University of Essex. 

Researchers tested 44 people who had previously reported symptoms or sensitivity to mobile phone emissions, and a control group of 114 people who had not reported any health effects.

The study found that physiological parameters such as heart rate, blood pressure and skin conductance were not affected by whether the mast was switched on or off, and did not detect any significant effects in either group of participants between GSM exposure and no exposure.

When both sensitive and control participants were exposed to a 3G signal, neither the physiological measures nor the number of reported symptoms increased.

However, the sensitive group did report increased levels of bodily activity when exposed to 3G.

Further analysis suggested that this was because a higher proportion of sensitive people received the UMTS signal during their first 50-minute testing session.

All other measures did not differ between when the 3G mast was on and when it was off.

All participants were tested in several different sessions. In open provocation tests, when both participant and experimenter knew whether the signal was on or off, sensitive individuals reported lower levels of well-being and more symptoms when the signal was on.

This confirmed that the laboratory conditions did not prevent them from experiencing typical symptoms in response to mobile phone masts.

However, when tests were carried out under double-blind conditions, where neither experimenter nor participant knew whether the signal was on or off, the number of symptoms reported was not related to whether the mast was on or off.

Two of the 44 sensitive individuals correctly judged whether the mast was on or off in all six tests, compared with five out of 114 control participants. This proportion is is expected by chance and was not increased in the sensitive group.

The study found that, compared with controls, sensitive individuals reported more symptoms and greater severity of symptoms, as well as higher skin conductance (which is a good measure of physiological response to environmental stressors) regardless of whether the signal was on or off.

Hence, the range of symptoms and physiological responses does not appear to be related to the presence of either GSM or 3G signals.

"It is clear that sensitive individuals are suffering real symptoms and often have a poor quality of life," said principal investigator Professor Elaine Fox. "It is now important to determine what other factors could be causing these symptoms."

The Essex research team is now undertaking a study into the short-term health effects of exposure to Tetra mobile radio masts, which are used for the emergency services' communications systems.

The results of the GSM and 3G tests are consistent with the only other published large-scale study of the effects of short-term exposure to mobile phone masts with sensitive individuals, published in Environmental Health Perspectives by Regel et al in 2006.