COPENHAGEN -- Long-term cell phone users are not at elevated cancer risk, according to a large Danish study.
COPENHAGEN, Dec. 5 -- Long-term cell phone users are not at elevated cancer risk, according to a large Danish cohort study.
Among 420,095 Danish mobile phone subscribers followed for up to 21 years, the cancer risk was slightly lower than the general population, with no increase for brain cancer, said Joachim Schz, Ph.D., of the Danish Cancer Society here, and colleagues, in the Dec. 6 issue of the Journal of the National Cancer Institute.
The study included all Danes who first subscribed to cellular service from 1982 to 1995. The researchers linked these records with national cancer registry data to calculate incidence rates compared to expected rates for the general population (standardized incidence ratios, SIR).
They found the overall cancer risk among subscribers was slightly, but significantly, lower than expected (SIR 0.95, 95% confidence interval 0.93 to 0.97).
Brain and central nervous system tumors were likewise no more common among cell phone users (SIR 0.96, 95% CI 0.87 to 1.05, for men and 1.03, 95% CI 0.82 to 1.26, for women). Among those who had subscribed for at least a decade, the findings were similar (SIR 0.66, 95% CI 0.44 to 0.95), and there was no trend for increased risk with time since first subscription.
Although there has been no evidence of increased risk among short-term users or in most studies of long-term use, two long-term studies, albeit with methodological problems, found some increased risk.
"It is thus reassuring that the findings from our cohort study are consistent with most case-control studies conducted worldwide even though different approaches for exposure assessment were used," the authors wrote.
"Moreover, the narrow confidence intervals provide evidence that any large association of risk of cancer and cellular telephone use can be excluded," they added.
The researchers found a total of 14,249 cancers among the 357,553 male and 62,542 female private cellular telephone subscribers in their study using the Danish Cancer Registry, which has virtually complete national incidence reporting.
The mean time since first subscription was 8.5 years. About 11,000 participants had subscribed for 15 or more years, and the 56,648 long-term subscribers (more than 10 years) had a mean follow-up of 13.0 years. Among the male subscribers, 85.1% had their subscription for less than 10 years, 11.9% for 10 to 14 years, and 3.0% for 15 to 21 years. Among women these figures were, 94.5%, 5.0%, and 0.5%, respectively.
Participants were followed until first nonmelanoma skin cancer diagnosis, death, emigration, or end of the study period in 2002. Those with a prior history of cancers, except nonmelanoma skin cancer, before their first subscription were excluded.
Cell phone use was not significantly associated with increased overall cancer risk for men (SIR 0.93, 95% CI 0.92 to 0.95) or women (SIR 1.03, 95% CI 0.99 to 1.07). Among men, the decrease in cancer risk was mainly attributable to lower smoking-related cancer risk (SIR 0.88, 95% CI 0.86 to 0.91), but there were significant decreased risks for several types of cancer including lung, buccal cavity, pharynx, esophagus, liver, and pancreas. Among women, the nonsignificant overall increase in risk was due to smoking-related cancers (SIR 1.11, 95% CI 1.02 to 1.21), cervical cancer (SIR 1.30, 95% CI 1.08 to 1.54) and kidney cancer (SIR 1.42, 95% CI 1.02 to 1.92).
Since it is the cell phone antenna that emits the radio frequency electromagnetic fields that have been of concern, the researchers looked at cancers in anatomic areas that are near the antenna during use. They found no significantly elevated risk for salivary gland tumors (SIR 0.77), eye tumors (SIR 0.96), glioma (SIR 1.01, 95% CI 0.89 to 1.14), meningioma (SIR 0.86, 95% CI 0.67 to 1.09), and cranial nerve sheath tumors, including acoustic neuroma (SIR 0.73, 95% CI 0.50 to 1.03).
Leukemia was not associated with use among the general cohort (SIR 1.00) or those with 10 or more years of follow-up (SIR 1.08, 95% CI 0.74 to 1.52).
Since the researchers could not link names to registry data for individuals with a subscription in the name of their company, these individuals were excluded. This may have reduced the proportion of users as well as excluded some of the most active users.
The researchers said they plan to continue following the study cohort.
The study was supported by the Danish Strategic Research Council and the Danish Cancer Society.