A case-control study was conducted in Iran to investigate the effect of extremely low frequency electromagnetic fields exposure on sleep quality of workers in high voltage substations.
The participants completed the Pittsburgh Sleep Quality Index questionnaire on three consecutive days.
| Group | Description |
|---|---|
| Reference group 1 | shift workers of cement, tire and copper industries |
| Group 2 | shift workers in high voltage substations |
| Cases | Controls | |
|---|---|---|
| Eligible | 67 | 110 |
41 workers in 132 kV substations, 20 workers in 230 kV substations, and 6 workers in 400 kV substations
Total number of measurement points was 2583 of which 1343 were related to the magnetic fields and 1240 to electric fields. The measured occupational exposure to electric field strength and magnetic flux density was below the reference levels of the ICNIRP guidelines.
No significant differences between the case and control groups were observed for poor quality sleep according to Pittsburgh Sleep Quality Index (90.5% of cases and 85.3% of controls), for the total sleep quality score mean, and for component scores. Meantime to fall asleep for cases (35.68 ± 26.25 min) was significantly higher than for controls (28.89 ± 20.18 min). Cases had average sleep duration of 5.49 ± 1.31 hours, which was lower as compared with control subjects (5.90 ± 1.67 hours).
The authors suggest to complete this study in subsequent research by including the impact of job stress variables (e.g., overtime, low social support, physically grueling jobs, part-time work) on sleep quality and by assessing the objective factors of sleep using polysomnography.
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