Epidemiological study

Re-examining the association between residential exposure to magnetic fields from power lines and childhood asthma in the Danish National Birth Cohort.

Published in: PLoS One 2017; 12 (5): e0177651

Aim of study (acc. to author)

The association between residential exposure to magnetic fields during pregnancy and childhood asthma was investigated in a cohort study in Denmark.

Further details

Asthma cases were identified using 3 independent data sources: mothers' reports, a national hospitalization registry and a national prescription drug registry. A definitive asthma case was a child who had an asthma diagnosis in all of the three data sources.

Endpoint/type of risk estimation

  • asthma
Type of risk estimation:
  • prevalence
(hazard ratio)



  • calculation: distance from the residence to the nearest power line based on GPS data, estimated magnetic flux densities based on line configurations, historical loading, phasing and direction of current flow provided by utility companies

Exposure groups

Reference group 1 magnetic field strength: no exposure
Group 2 magnetic field strength: 0.1 µT
Group 3 magnetic field strength: ≥ 0.2 µT


  • Group:
    • women
    • children in utero
  • Characteristics: cohort of mothers and newborns, enrolled between 1996 and 2002, follow-up at the age of 7 years
  • Observation period: 1996 - 2002
  • Study location: Denmark
  • Data source: Danish National Birth Cohort

Study size

Total 92,675
Statistical analysis method:
  • Cox proportional regressions analysis
( adjustment: )

Conclusion (acc. to author)

Among possible asthma cases, only 24 (0.12%) had mothers who were exposed to magnetic field strength of 0.2 µT or more during pregnancy and only 38 (0.19%) were exposed at any time during follow-up.
No differences or trends in the risk of asthma development were detected between children with different levels of MF exposure regardless of the asthma case definition or outcome data source.
The authors concluded that no evidence was found for an association between residential exposure to magnetic fields during pregnancy or early childhood and the risk of childhood asthma.

Study funded by

  • Electric Power Research Institute (EPRI), USA

Related articles

  • Li DK et al. (2011): Maternal exposure to magnetic fields during pregnancy in relation to the risk of asthma in offspring.