Children and adolescents who use mobile phones are at no bigger risk of developing brain cancer than those who do not use them, according to a study of patients aged 7 to 19.
But a critic of the study questions the findings. And other scientists say that more research is needed to reach definitive conclusions.
The research, published in the Journal of the National Cancer Institute on Wednesday and partially funded by mobile phone operators, addresses concerns that children may be more vulnerable to health risks from electromagnetic radiation from cellphones.
Children's nervous systems are still developing, and there are fears that their smaller head circumferences could allow radiation to penetrate deeper into their brains.
But the study – the first to look specifically at children and the risk of cancer from cellphones – found that brain tumour patients were no more likely to be regular phone users than control subjects who did not have cancer.
"If mobile phone use would be a risk factor, you'd expect cancer patients to have a higher amount of usage," said Martin Roosli, who conducted the study at the Swiss Tropical and Public Health Institute in Basel, Switzerland.
Some funding for the study came from the Swiss Research Foundation on Mobile Communication, which is partly supported by Swiss mobile phone operators. They were not involved in the study design or the collection, analysis or interpretation of the data, according the authors.
About 5 billion cellphones are in use today, some 30 years after they were introduced commercially.
The World Health Organization (WHO) reignited interest in possible health risks from cellphones after it said in May that using a mobile phone might increase the risk of certain types of brain tumors.
Dr. Roosli's research, conducted between 2004 and 2008 in Norway, Denmark, Sweden and Switzerland, looked at phone use of 352 brain cancer patients and 646 control subjects.
About 55 per cent of the patients reported regular mobile phone use compared with 51 per cent of the control subjects, according to the study, which defined regular users as making an average of at least one call per week.
The study also found that 75.3 per cent of cancer patients used mobile phones more than 20 times in their lives before they were diagnosed, and that 72 per cent of control subjects reported using them more than 20 times in their lives.
"What we found was that there was no (significant) difference in the amount of use," said Dr. Roosli, adding that if there is a risk, "it would be a really small risk."
The study involved face-to-face interviews, and Roosli said that he could not be certain about the accuracy of the subjects' recollections of past cellphone use.
He also said teen and child cellphone use has likely increased since they did the study.
One critic of the report said the results were an "unwarranted conclusion."
"Brain tumours can take 10 years to form, and young children certainly have not been heavy cellphone users for very long," said Devra Davis, author of the book "Disconnect: The Truth About Cell Phone Radiation, What the Industry Has Done to Hide It, and How to Protect Your Family."
In a subset of the study, Dr. Roosli examined information from mobile service providers about the length of the subjects' cellular subscription when available.
From operator data, he found that the cancer risk doubled for people who used phones for more than three years, but said that this data was unreliable because more cancer patients had provided carrier records than control subjects.
Dr. Roosli said phone company records were not always available because some people changed their numbers and some operators were required by law to delete call records after six months.
The study found no evidence of any increase in the risk of tumours in brain areas most exposed to cellphone radiation.
Dr. Roosli said that future studies should examine longer-term phone use among children. He suggested collecting phone records from a bigger group to see who develops tumours.
"(This study) provides quite some evidence that use of less than five years does not increase the chance of a brain tumour, but naturally we don't have a lot of long-term users," he said.
In an editorial published with the article, U.S. scientists recommended that investigators keep monitoring population incidence rates.
In the meantime, they said, people who are concerned should consider using an ear piece or the phone's speaker function.
Asked about practices in his own family, Dr. Roosli said "our study does not provide strong evidence of a relation, so why should I forbid my children from using cellphones?"