In 2007, WHO completed its comprehensive, international project on magnetic fields associated with electricity supply (extremely low-frequency fields). The project aimed to evaluate whether magnetic and electric fields cause cancer and determine whether the fields in any other ways are detrimental to public health.

WHO's evaluations were published in Environmental Health Criteria no. 238, a 446-page long document. WHO has therefore summarised the conclusions in fact sheet no. 322.

The evaluation - in brief
To be even briefer than the fact sheet, WHO concludes that no new studies have been published that could potentially change the evaluation performed by the International Agency for Research on Cancer (IARC) in 2002. At that time, the IARC classified magnetic fields associated with electricity supply as 'possibly carcinogenic to humans'. The classification was based on demographic (epidemiological) studies, which demonstrated an increased incidence of leukaemia in children having been exposed to low-frequency magnetic fields in their homes of more than 0.3 to 0.4 μT (microtesla) on average. However, WHO assesses that the epidemiological results were weakened by methodology problems.

There are no known biophysical mechanisms indicating that magnetic fields cause cancer. If exposure to these fields involves a health risk, such risks must therefore be attributed to an as yet unknown biological mechanism. Additionally, animal tests have been largely negative. As such, WHO concludes that - on the whole - the childhood leukaemia research results are not sufficiently strong to indicate a causal link. There might be other reasons for the results.

Where other diseases are concerned, WHO states that there is much less evidence pointing to a link with magnetic fields.

Precautionary approach
WHO does not find that there is a scientific background for defining exposure limits for the relatively weak fields emanating from electricity supply installations and instead recommends a precautionary approach. Therefore WHO recommends:

• that authorities and the electricity industry keep abreast with and support research to eliminate scientific uncertainty
• that member states ensure good communication between all interested parties
• that the possibilities of reducing the fields are explored when new electricity supply installations or apparatus are constructed provided this can be done at no or little cost The introduction of arbitrary low exposure limits is not justified.