Friday, June 25, 2010

No Cancer Link With Cell Phone Towers

June 24, 2010 (London, United Kingdom) — There is no association between a pregnant mother's proximity to a cell phone tower and early childhood cancers, according to results of the largest study of its kind to date.

Paul Elliott, MD, PhD, professor of epidemiology and public health medicine from Imperial College, London, United Kingdom, led the research. The paper was published online June 22 in BMJ.

"We found no pattern to suggest that the children of mums living near a [cell phone tower] during pregnancy had a greater risk of developing cancer than those who lived elsewhere," Dr. Elliot told Medscape Oncology.

He added that unlike previous studies of associations between cancer and cell phone towers, this study used larger numbers of cases so was not subject to the selection and reporting biases seen with smaller sample sizes.

Case–Control Study

In this British study, data on nearly 1400 children younger than 4 years were drawn from the national cancer registry. All case subjects had leukemia or tumors of the central nervous system or brain from 1999 and 2001. Each child with cancer was matched with 3 control subjects for sex and date of birth from the national birth register.

The distance between registered address at time of birth and the nearest of 81,781 cell towers was assessed for each case. Likewise, total power output across all towers within 700 meters (765 yards) of the cell tower was recorded. The researchers then computed modeled power density at each birth address for towers within 1400 meters (1531 yards). Exposure beyond 1400 meters was considered to be at background levels.

This information was correlated with the incidence of cancers of the brain and central nervous system, leukemia, and non-Hodgkin's lymphomas, and all cancers combined.

In their paper, the authors acknowledge that despite low levels of exposure from cell phone towers, there are theoretical concerns about the effects on children because of the relatively greater dose (per kg body mass), the potentially greater susceptibility of children than of adults, and the potential effects of lifelong cumulative exposure to radiofrequency electromagnetic fields.

Only cancers with a short latency period, typically within the first 4 years of life, were investigated. In addition, the study was restricted to exposure of children in utero, although the authors state that postnatal exposure might be relevant to the incidence of early childhood cancers.

"We only looked at estimated exposures during the fetal period and were unable to look at exposure patterns for the children after birth. This is clearly a limitation and it would have been good to look at data after birth, if they had been available. However, our findings do not suggest any link between early childhood cancers and [cell phone tower] exposure," added Dr. Elliott.

Encourage Patients Not to Worry

In an accompanying editorial, John Bithell, MA, DPhil, honorary research fellow at the Childhood Cancer Research Group, University of Oxford, United Kingdom, points out that of the 3 surrogates of exposure considered in the study, the most convincing is the modeled power density at varying distances from the nearest tower. "This is probably the best measure used in an epidemiological study to date."

However, he adds that individual exposure could still vary substantially according to building design, lifestyle, and migration, so the prospects for good estimates of individual exposure are poor.

Based on these results, he concludes that the medical profession should encourage their patients not to worry about harm caused by proximity to cell phone towers. "The epidemiological evidence is also supported by experimental evidence, which has so far failed to show any biological effects — in vivo or in vitro — that might lead us to worry about the impact on health," concluded Dr. Bithell.

However, Sam Milham, Jr. MD, MPH, former chronic disease epidemiologist at the Washington State Department of Health and clinical associate professor at the University of Washington, School of Public Health, Seattle, believes the study used the wrong metric.

"All cell towers operate on direct current, which is changed from the grid alternating current (AC) by switching power supplies. These interrupt the AC current and create high-voltage transients, which get back into the grid. The transients are a potent carcinogen," he explained.

Dr. Milham, who was approached by Medscape Oncology for comment, is currently investigating a cluster of cancers in school teachers in Palm Springs, California. He explained the relation between distance from tower, transient levels, and cancer cases.

"It has a cell tower 20 feet from a classroom wing. The transient levels in the classrooms are inversely related to distance from the tower base, and the cancer cases are found to be overrepresented in the rooms near the tower. This is a close-in phenomenon. I also find very high transient levels in firehouses and businesses near cell towers."

"The BMJ study's high-dose group, by distance, was under 612 meters [669 yards]. If they can show me that the case–control risks were similar for residences less than 100 and 200 meters [109 and 218 yards, respectively] from the tower, I'll accept their findings," Dr. Milham said.

The study was funded through the UK Mobile Telecommunications Health Research (MTHR) Programme, an independent body set up to provide funding for research into the possible health effects of mobile telecommunications. The MTHR is jointly funded by the UK Department of Health and the mobile telecommunications industry. Dr. Elliott and Dr. Milham have disclosed no relevant financial relationships. Dr. Bithell reports a beneficial interest in shares in Vodafone Group not exceeding £3000 in value.