by ecancer reporter Janet Fricker

The risk of glioma with mobile and cordless phones increases with both length and frequency of use, concludes a Swedish study published in Pathophysiology.

The study furthermore found that risk tripled among people who had used a wireless phone for more than 25 years, and was highest among those who started using mobile or cordless phones before the age of 20.

Based on their findings authors Lennart Hardell and Michael Carlberg, from University Hospital, Orebro, now believe emissions from mobile phones should be re-classed as a group 1 carcinogen under the International Agency on Research on Cancer (IARC) classification system.

The increased use of mobile and cordless phones over the last decade has led to greater exposure of the brain to radiofrequency electromagnetic fields (RF-EMF).

Highest exposures are found on the side of the brain where the handheld phone is used (ipsilateral), while the opposite side (contralateral) receives less exposure.

Children, due to smaller head size, thinner skull bones and higher brain conductivity, are thought to absorb higher rates of RF-EMF than adults.

In May 2011 IARC evaluated the human cancer risk from RF-EMF exposure and concluded there was a Group 2B level of risk.

The IARC evaluation was based on a fairly short time from first exposure until diagnosis.

In the current study, Hardell and Carlberg undertook a pooled analysis of two case control studies on malignant brain tumours.

The first included patients aged 20 to 80 years diagnosed between 1997 and 2003; while the second included patients aged 18 to 75 years diagnosed between 2007 and 2009.

For all subjects mobile phone use was assessed through a mailed questionnaire estimating the average number of minutes per day phones were used, the ear mostly commonly used for calls, whether hands-free devices were used (regarded as non exposure) and use of cordless desk top phones was addressed by similar questions.

Altogether a total of 1,691 cases fulfilled the inclusion criteria, of which 1,498 (89%) answered the questionnaire.

Of these 1,380 (92%) had received a diagnosis of glioma, of which the most malignant variety, astrocytoma grade IV (glioblastoma multiforme) constituted over 50% of cases.

Altogether 3,530 control subjects were obtained from the Swedish Population Registry and matched according to geographical area, age and gender.

Latency (time from first use) was defined as the year of first use of a wireless phone to the year of diagnosis, and cumulative number of hours of use were also calculated.

The entire set of data was used in the regression analysis adjusted for gender, age, year of diagnosis and socioeconomic index.

Results show digital 2G phone use gave an OR of 1.3(95% CI 1.1-1.6) for glioma risk; but that among those who had used mobiles for longer than 25 years the OR was 3.0 (95% CI 1.7-5.2).

Use of cordless phones increased the risk to OR 1.4 (95% CI 1.1-1.7); with the highest risk found among those starting use when aged less than 20 years (OR 1.7, 95% CI 1.1 to 2.5).

The median latency time for diagnosis of glioma in use of mobile phones was 9.0 years (mean 10.1, range 2-28), while the median latency for cordless phones was 7.0 years (mean 8.0, range 2-21). Notably, results for digital 3G phones showed the highest risk among the >5-10 years latency group (OR 4.1, 95% CI 1.3-12).

This, say the authors, was the longest latency group for 3G use since the technology is new.

The results were based on small numbers. “This study clearly shows an increased risk for glioma associated with use of both mobile and cordless phones, a risk that increased significantly with latency and cumulative use,” write the authors.

There is reason to suspect, add the authors, that 3G phones could be more risky because in contrast to 2G phones they emit wide-band microwave (MW) signals that may lead to increased biological effects.

Reference

L Hardell, M Carlberg, et al. Cell and cordless phone risk for glioma-Analysis of pooled case-control studies in Sweden, 1997-2003 and 2007-2009. Pathophysiology.