Talking of cancer risk

Drivers who use hands-free cellular devices while driving may be doing themselves a favour in the long run.

That is because scientists still can't say with certainty that placing a mobile phone against the head is completely safe, especially for heavy users and people who began using the devices as children.

They point to lingering questions over the potential health effects from the energy emitted by the phones, specifically the risk of developing brain cancer.

“It's fair to say that the data aren't all in yet,'' says Dr David L. McCormick, a biologist and director of the Illinois Institute of Technology Research Institute in Chicago, who has studied the issue.

“There are a small number of epidemiological studies that have suggested a possible increase in cancer risk. But comparable studies in other populations haven't confirmed these findings.''

That is not to say anyone should panic. Mobile phones produce a type of radiation, but it is of the type called nonionising radio frequency — a form of energy located on the electromagnetic spectrum.

At the high end of the spectrum, ionising radiation, such as that emitted by X-ray machines, has well-known dangers.

But the weak signals released by nonionising radio frequencies do not cause DNA damage and there is no explanation for how such energy could cause cancer, McCormick says.

Most studies have not consistently demonstrated a link between mobile phone use and cancer.

Numerous laboratory studies on animals have also found no evidence that DNA is damaged by low levels of radio frequency, McCormick says.

But the sheer number of people now using mobile phones, the volume of use and a few studies that found a potential link between brain cancer and mobile phones have kept the safety question looming.

The National Academy of Sciences (NAS) released a report in January calling for more research on mobile phones and health risks.

The authors concluded that many of the past studies were not continued over a long-enough period of time to assess the risk of brain cancer, which typically develops slowly.

Nor have the studies examined the effects of mobile phone use on children, whose nervous systems are still developing, or on whether the radio frequency emissions can cause other types of health problems, such as cancers elsewhere in the body, says Dr Leeka Kheifets, a professor of epidemiology at the University of California, Los Angeles' School of Public Health, who was a member of the NAS panel.

“At this point, it looks unlikely that mobile phones are causing brain tumours, particularly from short-term exposures,'' Kheifets says.

“But we have not looked at all kinds of health outcomes yet. The focus has been on brain tumours because exposure from mobile phone use is mostly to the brain. And we are just beginning some studies on brain cancer in children.''

Kheifets and researchers in Denmark recently examined mobile phone use in children and found “unexpected results''.

The researchers examined 13,159 Danish children born in 1997 and 1998 who are participants of a study called the Danish National Birth Cohort.

The children's mothers were surveyed during pregnancy and again when the children were 18 months old and 7 years old.

The study found that children who used mobile phones, and whose mothers used mobile phones during pregnancy were 80 per cent more likely to have behavioural problems such as emotional symptoms, inattention, hyperactivity and problems with peers compared with children who had no mobile phone exposure as foetuses or in early childhood.

Children whose mothers used mobile phones during pregnancy but who had no other mobile phone exposure were 54 per cent more likely to exhibit behavioural problems.

The study, which is to be published in the journal Epidemiology, is the first to find a behavioural effect and, so, must be interpreted with caution.

But Kheifets says: “In general, children are more susceptible to environmental hazards. We have little information on mobile phones, and children are using mobile phones at younger ages.''

Research on children and long-term studies should provide more clarification on any health risks, says Dr Siegal Sadetzki, an epidemiologist at the Gertner Institute, Chaim Sheba Medical Centre, in Israel.

Sadetzki's research has found heavy mobile phone users were at 50 per cent higher risk for a parotid tumour.

The study was significant because it tracked heavy users for more than ten years and found a relationship between the side of the head the phone was typically placed against and where the tumour formed.

She says she doesn't think her study, which was published in February in the American Journal of Epidemiology, contradicts previous studies that showed no cause for alarm.

The research was conducted in Israel, which has a population of heavy users who were among the first to adopt mobile phone technology.

“Most negative results were seen for short-term users, below ten years of use,'' she said in an e-mail interview.

“It is well-known that the latency period for cancer development, and certainly for brain tumour development, is longer than that. The problem is, of course, that we are dealing with a relatively new technology.''

Sadetzki says: “I believe that mobile phone technology has a lot of advantages and is here to stay. But we, as a society, need to decide how to use it .... I think that the precautionary principle advising the use of simple measures to lower exposure should be adopted and taken seriously.''