LONDON, UK: The biggest study to date into the effects of mobile-phone usage on long-term health was launched on Thursday, aiming to track at least a quarter of a million of people in five European countries for up to 30 years.

The Cohort Study on Mobile Communications (COSMOS) differs from previous attempts to examine links between cellphone use and diseases such as cancer and neurological disorders in that it will follow users' behaviour in real time.

Most other large-scale studies have centred around asking people already suffering from cancer or other diseases about their previous mobile-phone use. They have also been shorter, since cellphones have only been widely used for about a decade.

"One of the limitations of research to date is that when you ask people about their mobile phone use say five years ago there's a lot of error," said Jack Rowley, director of research and sustainability at industry body the GSM Association.

About 5 billion mobile phones are in use worldwide. To date, groups such as the World Health Organisation, the American Cancer Society and the National Institutes of Health have found no evidence that cellphone use harms health.

"Research to date has necessarily mainly focused on use in the short term, less than 10 years," principal investigator Professor Paul Elliott of the School of Public Health at London's Imperial College told a news conference.

"The COSMOS study will be looking at long-term use, 10, 20 or 30 years. And with long-term monitoring there will be time for diseases to develop," he said.

The COSMOS study forms part of the Mobile Telecommunications and Health Research Programme (MTHR), a UK body funded by a variety of government and industry sources and run by independent experts, mostly university academics.

Professor Lawrie Challis from MTHR said: "Many cancers take 10, 15 years for the symptoms to appear. So we've got to address the question: Could there be something out there that we need to look at?"

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The GSMA's Rowley estimated that more than $100 million had been spent so far around the world on research into health risks from mobile phone usage.

Global spending on wireless equipment and services provided by companies such as Nokia, Ericsson and Huawei surpassed $1 trillion for the first time in 2009, according to technology research firm iSuppli.

The COSMOS study is recruiting participants aged 18-69 in Britain, Finland, the Netherlands, Sweden and Denmark through mobile carriers. It will use data from volunteers' phone bills and health records as well as questionnaires.

Rowley, while welcoming the planned study, said organisers might have trouble finding enough volunteers, citing a previous attempt to carry out a similar study on a smaller scale in Germany in 2004, which foundered on privacy concerns.

In Britain, COSMOS is inviting 2.4 million mobile phone users to take part, through the country's four top carriers: Vodafone, O2, T-Mobile and Orange. It hopes 90,000-100,000 will agree.

By late Thursday afternoon, 232 had signed up.

The study will examine all health developments and look for links to neurological diseases such as Alzheimer's and Parkinson's as well as cancer.

It will also take account of how users carry their phone -- for example in a trouser or chest pocket or in a bag -- and whether they use hand-free kits.

A spokesman for Britain's Health Protection Agency, an independent public body, said the study had the potential to give very reliable results.

"The Department of Epidemiology and Public Health at Imperial College is one of the best research centres in the world for this type of study," he said.

COSMOS will announce its findings as it progresses.