Epidemiological study (observational study)

Occupational electromagnetic field exposures associated with sleep quality: a cross-sectional study epidem.

By: Liu H, Chen G, Pan Y, Chen Z, Jin W, Sun C, Chen C, Dong X, Chen K, Xu Z, Zhang S, Yu Y

Published in: PLoS One 2014; 9 (10): e110825

Aim of study (acc. to author)

A cross-sectional study was conducted in China to investigate the relationship between self-assessed sleep status and electromagnetic field exposures, especially power frequency magnetic fields, in workers of a power plant.

Further details

Sleep quality was assessed by asking the participants to evaluate the sleep quality and the sleep duration during the past month. Sleep duration was categorized in short (< 7 h), medium (7-8 h), and long (≥ 8 h).

Endpoint/type of risk estimation

sleep disturbances: sleep quality and sleep duration

Type of risk estimation:

prevalence

(odds ratio (OR))

Exposure

- mobile communications
- mobile phone
- occupational
- personal

Assessment

questionnaire: occupational exposure hours per day, job titles, job description, walkie talkies usage per day, occupational exposure duration; years of mobile phone service, electric fee in family per month
measurement: electric field intensity and magnetic field intensity at different places in the power plant

Exposure groups

Group	Description
Reference group 1	daily occupational exposure time: ≤ 1.5 hours/day
Group 2	daily occupational exposure time: < 1.5 - ≤ 4 hours/day
Group 3	daily occupational exposure time: > 4 hours/day
Reference group 4	occupational exposure duration: < 23 years
Group 5	occupational exposure duration: ≥ 23 years
Reference group 6	electric fee: < 150 yuan/month
Group 7	electric fee: ≥ 150 yuan/month
Reference group 8	mobile phone use: < 12 years
Group 9	mobile phone use: ≥ 12 years

Population

Group:
- men
- women
Age: 22–60 years
Characteristics: workers in an electric power plant
Observation period: August - September 2011
Study location: China (Zhejiang province)
Exclusion criteria: retired persons or persons with any type of cancer, severe heart, liver or kidney disease

Study size

Type	Value
Total	1,073
Eligible	854

Statistical analysis method:

logistic regression

(adjustment:

age
smoking, tea drinking, BMI, work stress

)

Results (acc. to author)

The measured electric field strength was 316.3 ± 1212.3 V/m and magnetic field strength was 6.17 ± 14.71 µT in the exposure group, which far outstripped the values in the non-exposure group (3.9 ± 0.3 V/m and 0.061 ± 0.017 µT, respectively).
Subjects with long daily exposure time had a significantly higher risk of poor sleep quality (group 2: OR 1.68, CI 1.18-2.39; group 3: OR 1.57, CI 1.10-2.24) in comparison to those with short daily exposure time (group 1). Additionally, among the subjects with long-term occupational exposure, the longer daily occupational exposure time apparently increased the risk of poor sleep quality (> 1.5 - ≤4 hours/day: OR 2.12 CI 1.23-3.66; > 4 hours/day: OR 1.83, CI 1.07-3.15). There was no significant association of long-term occupational exposure duration, monthly electric fee or years of mobile-phone use with sleep quality or sleep duration.
The authors conclude that the results showed an association between daily occupational power frequency magnetic field exposure and poor sleep quality. It implies that power frequency magnetic field exposure may damage human sleep quality rather than sleep duration.

Study funded by

National Basic Research Program (Program 973), China
National Natural Science Foundation (NSFC), China

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