Epidemiological study (observational study)

Occupational Exposure to Magnetic Fields and Breast Cancer Among Women Textile Workers in Shanghai, China epidem.

By: Li W, Ray RM, Thomas DB, Yost M, Davis S, Breslow N, Gao DL, Fitzgibbons ED, Camp JE, Wong E, Wernli KJ, Checkoway H

Published in: Am J Epidemiol 2013; 178 (7): 1038-1045

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Aim of study (acc. to author)

A nested case-cohort study was conducted to investigate the association between occupational exposure to magnetic fields and the risk of breast cancer within a cohort of female textile workers in Shanghai, China.

Endpoint/type of risk estimation

breast cancer

Type of risk estimation:

incidence

(harzard ratio)

Exposure

- 50/60 Hz
- magnetic field
- occupational

Assessment

job exposure matrix: designed for cumulative magnetic field exposure
measurement: measurements of magnetic flux density were collected in 57 factories from1,115 workers for 102 of 116 positions
calculation: cumulative magnetic field exposure was calculated for each position a subject held as a product of the assigned exposure value and years of employment in that position

Exposure groups

Group	Description
Reference group 1	cumulative magnetic field exposure 1st quartil: > 0 - 2.70 µT-years
Group 2	cumulative magnetic field exposure 2nd quartil: > 2.70 - 4.13 µT-years
Group 3	cumulative magnetic field exposure 3rd quartil: > 4.13 - 6.24 µT-years
Group 4	cumulative magnetic field exposure 4th quartil: > 6.24 µT-years

Population

Group:
- women
Age: ≥ 30 years
Observation period: 1989 - 2000
Study location: China (Shanghai)

Case group

Characteristics: patients with breast cancer in a cohort of 267,400 workers from 503 textile factories
Data source: Shanghai Cancer Registry

Control group

Matching:
- age

Study size

	Cases	Controls
Eligible	1,763	4,780

Statistical analysis method:

Cox proportional regressions analysis

(adjustment:

)

Results (acc. to author)

The average level of magnetic field exposure for all 102 positions studied was 0.25 µT, the range of arithmetic means for 102 positions was between 0.02 µT and 0.9 µT. The positions with highest MF exposure were spinning machine operators (0.9 µT) and sewing machine operators (0.81 µT).
No association was observed between cumulative exposure to magnetic fields and overall risk of breast cancer (hazard ratio for group 4: 1.03, CI 0.87, 1.21). Similar null findings were observed when exposures were lagged and stratified by age at breast cancer diagnosis.
The authors conclude that the findings do not support the hypothesis that magnetic field exposure increases the risk of breast cancer.

Study funded by

National Cancer Institute (NCI; U.S. National Institutes of Health), Maryland, USA
National Institute for Occupational Safety and Health (NIOSH), USA
National Institutes of Health (NIH), Maryland, USA

Comments on this article

Feychting M (2013): Invited commentary: extremely low-frequency magnetic fields and breast cancer - now it is enough!

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