(OT) but interpreting it is difficult.
(farking amazing how "difficult" it is to interpret the results..pb)
timesonline.co.uk
Scientists puzzled over power lines link to leukaemia
By Nigel Hawkes, Health Editor
CHILDREN who live near power lines are at an increased risk of leukaemia, a study has proved — but the power lines are not to blame.
The largest study into the theory that power lines cause cancer has left scientists none the wiser about the link between the two. This is because the increase in risk extends to a distance of 600m (1,970ft) from the lines, so far away that the magnetic fields that they generate are insignificant. The results suggest another explanation. The authors of the research yesterday refused to rule out the possibility that their conclusion had arisen by chance.
The Childhood Cancer Research Group at Oxford and the National Grid collected data on childhood cancers between 1962 and 1995 and compared them with records of the houses where the parents of the children lived at the time the children were born.
Data from National Grid Transco enabled the team to identify whether among 9,700 cases of leukaemia there was any evidence that those living close to power lines were at greater risk.
The team, led by Gerald Draper and including John Swanson of National Grid Transco, conclude in the British Medical Journal that living within 200m of a power line is linked to a 70 per cent increase in risk, and living within 600m to a 23 per cent increase in risk.
The actual number of extra cases is small, fewer than 1 per cent of all cases of childhood leukaemia, since relatively few people live this close to power lines. Only 0.8 per cent of the population live within 200m, and a further 3.2 per cent between 200m and 600m. The total number of cases involved is 64 within 200m, and another 258 between 200m and 600m — a total of 322.
The number expected, if there were no increased risk would have been 253. So the extra cases number only 69, much less than 1 per cent of all leukaemia diagnosed in children over more than 30 years.
The lines involved are the major transmission lines carried on steel pylons, most of which operate at 275,000 volts. Local lines carried on wooden poles were not involved in the study, because their voltage is much lower.
The result was statistically significant, and “very surprising”, Dr Draper said yesterday, but interpreting it is difficult.
At 600m, the magnetic field from the lines is so small that it is no greater than that from domestic wiring. If magnetic fields of this size were a risk, it is one that everybody would share so that no extra risk would show up from power lines.
But if it is not the magnetic fields causing the increased risk, what is it? The obvious possibility is that this is a chance finding, with no meaning.
A second possibility is that people who live near power lines are different from those who do not. Childhood leukaemia is slightly more common among the children of the better-off. So if the homes near power lines tended to be occupied by wealthier people, it could explain the link.
Analysis of the data suggests, however, that this is not the explanation. Various other theories have been put forward, and cannot yet be ruled out.
Would the findings discourage either of the principal authors from living in a house near a power line? Dr Draper said that, on the basis of this information, he himself would take no action, nor advise anyone else to do so.
“But I don’t think I would move into a house with an exposure of more than 0.4 microtesla. That would be within 60 metres or so of a 275,000 volt power line” he said.
Dr Swanson said: “All things being equal, I would choose a house away from a power line, for aesthetic reasons as much as anything. But if it was a house I really wanted, it wouldn’t put me off.”
THE ALTERNATIVE LINES OF INQUIRY
People near power lines are different. Data appears to rule this out, but differences may be too subtle to be measured. More research needed
Power lines create charged ions that bind to pollutants and are the breathed in. This is the theory of Professor Denis Henshaw, of Bristol University. If so, the effect would be more marked downwind of power lines — it is not, according to a preliminary analysis
The result is chance. If enough studies are done on an issue some will produce positive findings simply by chance
Leukaemia is caused by a virus, so far unidentified, that is more easily caught by populations newly exposed to it — in new towns or construction sites, for example
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