13,259 cases and 100,882 controls
Overall, increased cancer risk was identified in the population with exposure to extremely low frequency magnetic fields (OR 1.08, CI 1.01-1.15). Grouping according to the countries showed that 20, 18 and 3 out of the 42 included studies were conducted in North American, European and Asian populations, respectively. An increased risk was found in North America (OR 1.10, CI 1.02-1.20), especially in the United States (OR 1.10, CI 1.01-1.20). On the contrary, no statistically significant association between exposure to extremely low frequency magnetic fields and cancer risk was found in the analysis of European studies.
A higher risk was found to be statistically significantly associated with the residential exposed population (OR 1.18, CI 1.02-1.37) in comparison to occupational exposure, exposure to electric blankets and other household appliances. In the included studies, exposure to extremely low frequency magnetic fields was assessed either by a questionnaire based interview or by measurement or by calculation of the magnetic flux densities. An increased cancer risk was found in interview-based studies (OR 1.16, CI 1.00-1.35). In measurement-based studies, a slight increased risk was found only in premenopausal breast cancer (OR 1.23, CI 1.01- 1.49).
In conclusion the meta-analysis suggests that exposure to extremely low frequency magnetic fields is associated with cancer risk, mainly in the United States and in residential exposed populations. Methodological challenges might explain the differences among studies.