Exposure to magnetic fields and childhood acute lymphocytic leukemia in São Paulo, Brazil

Background: Epidemiological studies have identified increased risks of leukemia in children living near power lines and exposed to relatively high levels of magnetic fields. Results have been remarkably consistent, but there is still no explanation for this increase. In this study we evaluated the effect of 60 Hz magnetic fields on acute lymphocytic leukemia (ALL) in the State of São Paulo, Brazil.

Methods: This case-control study included ALL cases (n=162) recruited from eight hospitals between January 2003 and February 2009. Controls (n=565) matched on gender, age, and city of birth were selected from the São Paulo Birth Registry. Exposure to extremely low frequency magnetic fields (ELF MF) was based on measurements inside home and distance to power lines.

Results: For 24h measurements in children rooms, levels of ELF MF equal to or greater than 0.3microtesla (μT), compared to children exposed to levels below 0.1 μT showed no increased risk of ALL (odds ratio [OR] 1.09; 95% confidence interval [95% CI] 0.33-3.61). When only nighttime measurements were considered, a risk (OR 1.52; 95% CI 0.46-5.01) was observed. Children living within 200 m of power lines presented an increased risk of ALL (OR 1.67; 95% CI 0.49-5.75), compared to children living at 600 m or more of power lines. For those living within 50 m of power lines the OR was 3.57 (95% CI 0.41-31.44).

Conclusions: Even though our results are consistent with the small risks reported in other studies on ELF MF and leukemia in children, overall our results do not provide support for an association between magnetic fields and childhood leukemia, but small numbers and likely biases weaken the strength of this conclusion.