Schuz J, Jacobsen R, Olsen JH, Boice JD Jr., et al. (2006d)

These authors previously reported the results of a cohort study of cell phone subscribers in Denmark (Johansen, 2002). They have now updated this study. They studied all cell phone subscribers during the period 1982-1995. After exclusion of corporate subscribers, those under 18, and others, there were 420,095 in the final cohort. These individuals were linked to the Danish cancer Registry to ascertain cancer rates. Follow-up began on the date of first subscription and ended on the date of first cancer diagnosis (except for nonmelanoma skin cancer), date of death, date of emigration, or December 31, 2002, whichever came first. The incidence rates of different cancers in the cohort were compared to the expected rates in the entire Danish population. The observed cases divided by the expected, with adjustments for age and sex, give a standardized incidence ratio (SIR). The ratio is 1 when the numbers of observed and expected cases are equal. The rates were calculated according to sex, 5-year age groups, and calendar periods of observation. Data on annual income stratified by sex and 5-year age group were obtained from Statistics Denmark. Differences in income distributions were analyzed by plotting average income by age for cell phone subscribers and for the total Danish population. Comparisons were also made between the results of self-reported use from a case-control study and the records of pone subscription.

A total of 14,249 cancers were observed (SIR = 0.95; 95%CI – 0.93-0.97). Cell phone use was not associated with increased risk for brain tumours (SIR = 0.97), acoustic neuroma (SIR = 0.73), salivary gland tumours (SIR = 0.77), eye tumours (SIR = 0.96), or leukaemias (SIR = 1.00). For long-term subscribers (10 years or more) the SIR for brain tumours was 0.66 (CI = 0.44 -0.95). The risk for smoking-related cancers was decreased among men (SIR = 0.88), probably due to increased income among subscribers and lower smoking rates, bur increased among women (SIR = 1.11). The authors considered that the latter finding was probably due to chance, because of the many statistical comparisons made in the analysis.

The authors point out the strengths of the study, including its large size, the long follow-up period, the lack of biases that are found in a case-control study, and the use of objective measures of exposure. They also point out its limitations, including the exclusion of corporate users, the lack of information on new users after 1995, and possible misclassification of users of a phone that was listed under the name of a particular subscriber.

The authors conclude that they found no evidence of an association between tumour risk and cell phone use, and also state:

“Moreover, the narrow confidence intervals provide evidence that any large association of risk of cancer and cellular telephone use can be excluded”.
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