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MAGNETIC fields have been fingered in the past as a possible trigger for cancer, causing public scares about living under power lines or working near strong magnets. But no one could figure out how they might cause health problems because they don鈥檛 have enough energy to break chemical bonds or heat molecules up. Now chemists have a hint of a possible mechanism.

They found that proteins in membranes can act like magnets themselves, and that steady external magnetic fields of fridge-magnet strength can force them to bend into line. If the same happens in the membranes of living cells, magnetic fields could have a host of knock-on effects such as slowing down ion transfer and disrupting cell signalling.

Researchers already knew that some biological membranes can align themselves with a magnetic field just like iron shavings near a magnet. To find out how, Ron Naaman and his colleagues from the Weizmann Institute of Science in Israel studied the effect of a magnet on a simpler version of a membrane鈥攁 sheet of closely packed polypeptide molecules, which are shaped like long coils that can wind either clockwise or anticlockwise. These sheets have a similar structure to the proteins embedded in biological membranes.

The researchers left polypeptide sheets in an external magnetic field for a few hours, and found that the molecules leaned over, just like biological membranes did. Surprisingly, the direction of the lean depended on the wind of the coil. Naaman thinks this happens because the membrane develops its own magnetism. Polypeptide chains have a slight negative charge at one end and a positive charge at the other. If they are forced to sit next to each other in a sheet, electrons flow along the helix from the negatively charged end in an attempt to minimise the charge difference. This acts just like a current running through a coil of wire, inducing a permanent magnetic field within the peptides. Its direction depends on the wind of the helix (see Diagram).

鈥淭hat is a striking observation,鈥� says Jim Valles, a biologist from Brown University in Rhode Island. But he鈥檚 not convinced that Naaman鈥檚 work proves the polypeptide coils really did become magnetic, or that the same mechanism would work in living cells. 鈥淚 consider it highly speculative,鈥� he says. Thomas Tenforde, a biophysicist from Pacific Northwest National Labs, adds that the effects might not be large enough to have significant biological effects. But, he says, 鈥渋f there are subtle effects that we鈥檝e missed, then it鈥檚 important to find them鈥�.

Epidemiological studies on people exposed to magnetic fields have been inconclusive. But studies with rats have occasionally revealed effects such as boosted immunity and higher rates of miscarriages.

The fields Naaman used were between 0.09 and 0.45 tesla鈥攁bout the strength of the field just next to a strong fridge magnet, but 10,000 times stronger than the Earth鈥檚 magnetic field or those produced by a mobile phone. MRI scans, in contrast, expose patients to fields of up to 3 teslas. If Naaman鈥檚 model does apply to biological systems, our bodies could be subtly affected by anything from doorbells to car engines, he says. He now plans to collaborate with biologists to see whether magnetic fields affect ion transport in membranes.

Naaman doesn鈥檛 think his theory would apply to higher frequency electromagnetic radiation鈥攕uch as the kind that comes from mobile phones鈥攂ecause the direction of the external field flips too rapidly. But, he adds, any step towards understanding how magnetism might affect health would help researchers looking at these fields too.

Britain鈥檚 National Radiological Protection Board is to conduct a review of the health effects of static magnetic fields some time in the next 18 months, according to Richard Doll of Oxford University. 鈥淚 know of no health hazards. But they鈥檙e being used at progressively higher and higher strengths,鈥� he says. 鈥淲e think it鈥檚 important to look at it now.鈥�