Epidemiological study

Childhood leukemia risk in the California Power Line Study: Magnetic fields versus distance from power lines epidem.

By: Crespi CM, Swanson J, Vergara XP, Kheifets L

Published in: Environ Res 2019; 171: 530-535

Aim of study (acc. to author)

In a large case-control study in the USA, several research questions formulated to disentangle the relationships among magnetic fields, distance from high voltage power lines and childhood leukemia risk.

Further details

Following research questions were studied:
(1) Is the risk of childhood leukemia associated with exposure to magnetic fields from power lines independent of distance to the closest high voltage transmission line?
(2) Is the risk of childhood leukemia associated with exposure to magnetic fields from power lines independent of the voltage of the closest transmission line?
(3) Does risk decrease at the same rate as magnetic fields decrease with distance, or does it decrease more rapidly or less rapidly?
Previous analyses of this case-control study are published in Crespi et al. (2016) und Kheifets et al. (2017).

Endpoint/type of risk estimation

childhood leukemia

Type of risk estimation:

incidence

(odds ratio (OR))

Exposure

Assessment

calculation: (1) geocoding of the distance between mother's residential address at time of birth to closest power line, (2) magnetic flux density calculation based on distance and detailed information on physical configuration and dimension of power lines near residence, phasing, loading, and directional load flow data for years of birth and diagnosis (see Vergara et al. (2015)))

Exposure groups

Group	Description
Reference group 1	distance of residential birth address from closest power line: ≥ 600 m
Group 2	distance of residential birth address from closest power line: 500 - 600 m
Group 3	distance of residential birth address from closest power line: 400 - 500 m
Group 4	distance of residential birth address from closest power line: 300 - 400 m
Group 5	distance of residential birth address from closest power line: 200 - 300 m
Group 6	distance of residential birth address from closest power line: 100 - 200 m
Group 7	distance of residential birth address from closest power line: 50 - 100 m
Group 8	distance of residential birth address from closest power line: 0 - 50 m
Reference group 9	magnetic flux density: < 0.1 µT
Group 10	magnetic flux density: ≥ 0.1 - < 0.2 µT
Group 11	magnetic flux density: ≥ 0.2 - < 0.4 µT
Group 12	magnetic flux density: ≥ 0.4 µT

Population

Group:
- children
Age: 0–14 years
Observation period: 1986 - 2008
Study location: USA (California)

Case group

Characteristics: children of the California Power Line Study (CAPS)
Data source: California Cancer Registry
Exclusion criteria: insufficient address data for accurate geocoding

Control group

Selection:
- population-based
Matching:
- sex
- age

Study size

	Cases	Controls
Evaluable	4,879	4,835

Statistical analysis method:

logistic regression
regression spline analysis, interaction analysis

(adjustment:

age
sex
socioeconomic status
race

)

Results (acc. to author)

There were a total of 28 subjects (cases and controls) with calculated magnetic fields ≥ 0.4 μT and a total of 38 subjects within 50 m of power lines ≥ 200 kV. Sixteen subjects were both within 50 m of power lines ≥ 200 kV and had calculated magnetic fields ≥ 0.4 μT.
(1) In examining an interaction between distance and magnetic fields exposure, we found that neither close proximity to high voltage power lines alone nor exposure to high calculated magnetic fields alone were associated with childhood leukemia risk. Rather, elevated risk (OR 4.06, CI 1.16-14.3) was confined to the group that was both very close to high voltage lines (< 50 m) and had high calculated fields (≥ 0.4 μT).
(2) Further, high calculated fields (≥ 0.4 μT) that were due solely to lower voltage lines (< 200 kV) were not associated with elevated risk; rather, risk was confined to high fields attributable to high voltage power lines (≥ 200 kV).
(3) The analysis showed that the calculated fields were decreasing roughly proportional to inverse distance from power lines ≥ 200 kV..
The authors conclude that their findings argue against magnetic fields as a sole explanation for the association between distance and childhood leukemia and in favor of some other explanation linked to characteristics of power lines.

Study funded by

Electric Power Research Institute (EPRI), USA
National Cancer Institute (NCI; U.S. National Institutes of Health), Maryland, USA

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