Some cancers seem to be linked to extremely low frequency electromagnetic fields, suggests research published ahead of print in Occupational and Environmental Medicine.

The findings are based on more than 20,000 Swiss railway workers, who were monitored for 30 years.

The researchers opted to study this group, because railway workers in Switzerland tend to change jobs infrequently and are exposed to much higher levels of electromagnetic field radiation than the general population.

The researchers checked the full employment records of 20,141 Swiss railway workers in employment or retired from post between 1972 and 2002. Information on deaths among the employees was obtained from national data.

Electromagnetic field exposure varied, depending on post.

Drivers were exposed to around three times the levels of shunting yard engineers and nine times the levels of ticket collectors on trains. Station masters were exposed to the lowest levels.

Deaths from all causes were slightly higher among shunting yard engineers and train ticket collectors than among drivers. And there was little difference in deaths from cancers.

There was no link between electromagnetic field exposure and deaths from lymphoid leukaemia, non-Hodgkin's lymphoma, and brain tumours.

But there was some evidence that higher levels of electromagnetic field exposure had an impact on rates of myeloid leukaemia and Hodgkin's lymphoma.

Drivers were more than four times as likely to die of myeloid leukaemia, and over three times as likely to die of Hodgkin's lymphoma, as station masters.

The authors emphasise that passengers are in no danger, but suggest that efforts should be made to minimise levels of exposure among train drivers in new rolling stock.

Reference: Leukaemia, brain tumours and exposure to extremely low frequency magnetic fields: cohort of Swiss railway employees.