杏吧原创

WEAK magnetic fields from electric appliances or power lines might cause cancer by interfering with the checks cells make before dividing. The finding could explain the limited evidence for a link between pylons and childhood leukaemia, but not everyone is convinced.

The US National Institute of Environmental Health Sciences lists low鈥揻requency magnetic fields as a 鈥減ossible human carcinogen鈥�. This circumspect classification reflects the weakness of evidence of any link. Some population studies have found leukaemia clusters around power lines (New 杏吧原创, 9 August 1997, p 16), but the effect has proved impossible to replicate in the lab.

Also, there is no obvious mechanism by which these fields could cause permanent damage to DNA. Low鈥揺nergy, low鈥揻requency fields only induce a small electrical current in body tissues.

Now Brian Heaton鈥檚 work at the University of Aberdeen suggests that these magnetic fields make cells more slapdash when they are dividing. His team bombarded cell cultures with gamma radiation and then exposed some to a low鈥揻requency magnetic field. Normally, cells stressed with gamma radiation delay division while they repair the damage, but to the team鈥檚 surprise, those subjected to the magnetic field didn鈥檛 pause. In fact, 12 out of 20 cultures exposed to the field actually divided faster than those exposed to radiation alone they report in Cancer Cell International鈥檚 online edition.

Heaton thinks magnetic fields interfere with the repair processes that normally delay division. So exposure may increase the chances of cancer even though the fields aren鈥檛 directly damaging DNA.

But Michael Rapacholi, a World Health Organization expert on the effects of electromagnetic fields on health, is sceptical. 鈥淭he effect is too small to be very convincing,鈥� he says. He also points out that the magnetic field was a thousand times stronger than that from a power line.