Canada's largest city has recommended that parents limit the cellphone use of their children, but Health Canada said in response that science does not show that cellphones are unsafe.

Toronto Public Health has released a report that recommends that children cut down on their cellphone use to avoid exposure to radio frequencies, which the city says may prove to be a health risk. It recommends that children, where possible, use land lines, limit the length of cellphone calls, use headsets or hands-free options, and keep cellphones only for "essential purposes."

Ontario Premier Dalton McGuinty, responding to the city's report, agreed last week parents should limit their children's use of cellphones until more scientific research can establish if they are safe.

"I'm hardly a scientific expert on the consequences of prolonged cellphone use by children," Mr. McGuinty said. "But if I read a story, just as a dad, in the paper, I might want to speak to my kids, tell them to minimize their use, and kind of stay tuned to what the scientific community has to say on this score."

But while the Toronto agency officers and the Premier were only the latest officials to worry about the risks of cellphone use, federal public health officials in Canada and the United States have said the evidence of harm is unproven.

"Health Canada currently sees no scientific reason to consider the use of cellphones as unsafe," the organization's media officer Paul Spendlove wrote in an e-mail. "There is no convincing evidence of increased risk of disease from exposure to radio frequency electromagnetic fields from cellphones."

In the United States, the National Cancer Institute issued a lengthy fact sheet that summarizes worldwide research into cellphones and the possible link to tumours in the brain.

"Overall, research has not consistently demonstrated a link between cellular telephone use and cancer or any other adverse health effect," the institute says.

Regarding use by children specifically, the U. S. health agency said there is "no evidence that cellular telephone use poses more of a threat to children than to adults," although it does allow that children have not been the subjects of large studies and they "are likely to accumulate many years of exposure during their lives."

Loren Vanderlinden, the Toronto report's lead author, said there is hardly any research on the health impact of children's cellphone use, but that two 2007 meta-analyses of studies of adult cellphone users' health show "an association" between people who have used cellphones for 10 years or longer and both glioma and brain tumorous.

"It's an odds ratio, which shows there are higher odds for certain kinds of brain tumour," said Ms. Vanderlinden, a supervisor of environmental health assessment and policy at Toronto Public Health.

Furthermore, she said, despite the "acknowledged research gap" regarding child cellphone users' health, children would tend to be more vulnerable to brain and nervous-system cancers because their nervous systems are still developing.

But Mr. Spendlove said Health Canada has no advisories with respect to cellphone usage by school children. He said the organization identifies "concentration" as the chief personal safety issue for children using cellphones.

"For example," he said, "similar to adults not using a cellphone while driving, children should not use them while riding bicycles."

Health Canada, he said, bases its position on "the bulk of scientific evidence from animal, in vitro and epidemiological studies that have been carried out worldwide, including at our laboratory."

Marc Choma, director of communications for the Canadian Wireless Telecommunications Association, said he has "no reservations" about children using cellphones, adding that neither Health Canada nor the World Health Organization have identified any risks with cellphone use.

But the City of Toronto's report says that, while the evidence is far from conclusive, other jurisdictions are also starting to promote caution for child cellphone users.

The British Department of Health, it says, recommends that child cellphone users limit their exposure by keeping all calls short. The Belgian Federal Public Service and the Health General Directorate in France, it says, recommend that children and pregnant women limit their cellphone use and use land lines wherever possible. And the Russian Ministry of Health, it says, recommends that individuals under 18 not use cellphones at all.

"Everybody's clear on the uncertainty and the inconclusive nature of the science," Ms. Vanderlinden said, "but that it shouldn't stop precautionary policy and advice to parents on simple ways that [parents] might pay attention to their children's use of cellphones."