Study type: Epidemiological study (observational study)

Exposure to magnetic fields and childhood acute lymphocytic leukemia in Sao Paulo, Brazil. epidem.

Published in: Cancer Epidemiol 2011; 35 (6): 534-539

Aim of study (acc. to author)

A case-control study was conducted in Brazil to investigate the effect of exposure to 60 Hz magnetic fields on the occurrence of childhood acute lymphocytic leukemia.

Further details

It is common in Brazil for families of children with leukemia to move close to the treating hospital, thus subjects who moved after diagnosis were not included in the study as it was logistically infeasible to conduct measurements in the homes where they had lived prior to diagnosis.

Endpoint/type of risk estimation

Type of risk estimation: (odds ratio (OR))

Exposure

Assessment

Exposure groups

Group Description
Reference group 1 mean of 24 h magnetic field measurement: < 0.1 µT
Group 2 mean of 24 h magnetic field measurement: 0.1 - < 0.3 µT
Group 3 mean of 24 h magnetic field measurement: ≥ 0.3 µT
Reference group 4 mean of 24 h magnetic field measurement (only children who had never moved): < 0.1 µT
Group 5 mean of 24 h magnetic field measurement (only children who had never moved): 0.1 - < 0.3 µT
Group 6 mean of 24 h magnetic field measurement (only children who had never moved): ≥ 0.3 µT
Reference group 7 mean of magnetic fields measurements at night (from 8.00 PM to 8:00 AM): < 0.1 µT
Group 8 mean of magnetic fields measurements at night (from 8.00 PM to 8:00 AM): 0.1 - < 0.3 µT
Group 9 mean of magnetic fields measurements at night (from 8.00 PM to 8:00 AM): ≥ 0.3 µT
Reference group 10 mean of magnetic fields measurements at night (from 8.00 PM to 8:00 AM, only children who had never moved): < 0.1 µT
Group 11 mean of magnetic fields measurements at night (from 8.00 PM to 8:00 AM, only children who had never moved): 0.1 - < 0.3 µT
Group 12 mean of magnetic fields measurements at night (from 8.00 PM to 8:00 AM, only children who had never moved): ≥ 0.3 µT
Reference group 13 distance of residence to closest power line: ≥ 600 m
Group 14 distance of residence to closest power line: 200 - < 600 m
Group 15 distance of residence to closest power line: 100 - < 200 m
Group 16 distance of residence to closest power line: < 100 m
Reference group 17 distance of residence to closest power line (only children who had never moved): ≥ 600 m
Group 18 distance of residence to closest power line (only children who had never moved): 200 - < 600 m
Group 19 distance of residence to closest power line (only children who had never moved): 100 - < 200 m
Group 20 distance of residence to closest power line (only children who had never moved): < 100 m

Population

Case group

Control group

Study size

Cases Controls
Eligible 248 2,500
Participants 162 565
Statistical analysis method: (adjustment: )

Conclusion (acc. to author)

11 out of 162 cases and 34 out of 565 controls were exposed to extremely low frequency magnetic fields of 0.3 µT or more. No increased risk of acute lymphocytic leukemia (OR 1.09; CI 0.33-3.61) was observed for exposures equal to or greater than 0.3 µT estimated by 24 h measurements in children's bedrooms. However, when analysis was restricted to nighttime bedroom measurements, an increased risk (OR 1.52; CI 0.46-5.01) was observed at the same exposure level. When restricted to cases and controls who never moved, nighttime exposure risk (OR 1.72; CI 0.30-9.87) was even higher.
Only 5 out of 121 cases residing in the metropolitan region of Sao Paulo and 24 out of 418 controls were living within 100 m of power lines. Increased risk of acute lymphocytic leukemia was observed for children living within 100 m from power lines (OR 1.54; CI 0.26-9.12) and between 100 and 200 m (OR 1.67; CI 0.49-5.75). When analysis was restricted to cases and controls who had never moved, the risk was higher for children living between 100 and 200 m (OR 3.68; CI 0.68-19.82), but remained unchanged for those closer than 100 m from power lines (OR 1.52; CI 0.11-21.24).
The authors concluded that the results overall do not provide support for an association between magnetic fields and childhood leukemia. However, small numbers and likely biases weaken the strength of this conclusion. Increased risks were found in some subgroup, but results were inconsistent, imprecise and statistically not significant.

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