The World Health Organisation (WHO) yesterday called for more research into the health impact of using mobile telephones, amid fears that the devices can adversely affect the brain.
The Geneva-based body said it had also revised its recommendations on the use of mobile phones, predicted to draw 1.6 billion subscribers worldwide by 2005.
One recommendation is to highlight the need for new studies to confirm recent findings that mobile phones may cause changes in brain activity, reaction times and sleep patterns.
"All the information we have to date shows no adverse health effects from the use of mobile phones," a WHO official, Michael Repacholi said in a statement.
"However, most studies have examined the results of whole body exposure to radio frequency fields at levels far higher than those normally associated with wireless communications," he added.
Few studies have addressed the consequences of localised exposure to the head, he said.
WHO is carrying out research into radio frequency and a study in more than 10 countries is being co-ordinated by the International Agency for Research on Cancer.
It is expected to be finished in 2003.
In the meantime, WHO recommended that mobile users limit their own or children's exposure to radio frequency fields by limiting the length of calls or using "hands-free" devices to keep mobile phones away from the head and body.
WHO said exposure to radio frequency fields for a mobile phone user holding the phone tens of centimetres from the head is far lower than to a user who has the headset against the head.
"While one 1997 study found that radio frequency fields increased the rate at which genetically engineered mice developed lymphoma, the health implications of this result is unclear," it said.
Several studies are underway to confirm the finding and determine any relevance to cancer in human beings.
Three recent epidemiological studies found no convincing evidence of an increase in risk of cancer or any other disease with the use of mobile phones, it added.
Research currently indicates when mobile phones are used close to some medical devices such as pacemakers there is a possibility of causing interference, WHO said.