Power cables reduce brain tumor risk

OK I was a bit naughty with the headline. The headline in the normally reliable Guardian Unlimited Life was “Power cables linked to cancer”, but I think mine describes the results of the study equally well. First, the sensationalist story:

Children living near high-voltage power lines are substantially more likely to develop leukaemia, researchers from Oxford University and the national electricity grid report today in the British Medical Journal.

Those living within 200 metres of the overhead cables were 70% more likely to develop the disease than similar children living more than 600 metres away.

Wow! 70% more likely to develop the disease! Predictably the chairman of Children with Leukaemia weighed in with the not really hysterical:

There is now a clear case for immediate government action. Planning controls must be introduced to stop houses and schools being built close to high-voltage overhead power lines.

“Immediate government action”? Really?  Of course, it helps if you read the actual study, which concludes:

The annual incidence of childhood leukaemia in England and Wales is about 42 per million; the excess relative risks at distances of 0-199 m and 200-599 m are about 0.69 and 0.23, respectively, giving excess rates of 28 and 10 per million.

By my calculation that puts the normal risk of getting leukemia at 0.0042%, rising to a whopping 0.007% if the child lives within 199m of power lines. That’s a pretty small risk not really conveyed by the “70% increase” headline. (Although I do agree that if you’re one of the five extra cases a year it’s 100% for you.)

The figures can be found in this table under the “leukaemia” column that shows 64 cases of leukemia in the 0-199 meter range compared with 39 in the control group. If you look under the CNS (central nervous system)/brain tumors column you will see the equivalent figures are 33 cases against 45 for the control – a reduction of 17% (hence my headline). Take just the figure for 0-49 meters and the headline could just as easily have been “Power cables linked to 56% reduction in central nervous system and brain tumors” – although that would have been equally misleading. There is no causal link for either statement and so it seems absurd to be calling for “immediate government action”.  As we know, correlation is not causation. That doesn’t mean there is definitely no link but it should give us pause.

If there is a link, could it be due to the magnetic fields created by the power lines? The researchers measured magnetic fields near the power lines, but noted that although the increased risk seemed to extend to at least 200 meters, at that distance the magnetic fields from the power lines were less than fields from other sources (appliances, house wiring etc), in the homes. Also, the increased incidence of the disease was noted right up to the 600 meter limit – much more than previous studies had found and way beyond any electromagnetic field from the lines. The study doesn’t support the view that increased risk is due to electromagnetic fields.

It may not be the power lines, but something about areas where power lines are located, or something about the people who live in these areas. It’s hard to know what, since the researchers did control for socioeconomic status, and found that had no effect on the relative risks.

The study concluded:

While few children in England and Wales live close to high voltage power lines at birth, there is a slight tendency for the birth addresses of children with leukaemia to be closer to these lines than those of matched controls. An association between childhood leukaemia and power lines has been reported in several studies, but it is nevertheless surprising to find the effect extending so far from the lines. We have no satisfactory explanation for our results in terms of causation by magnetic fields or association with other factors. Neither the association reported here nor previous findings relating to level of exposure to magnetic fields are supported by convincing laboratory data or any accepted biological mechanism.

(My bold.)

There is no accepted biological mechanism to explain the results. The results could be due to chance (for example, if the controls were not representative) or confounding. Even if the link is causal, only about 1% of childhood leukemia in England and Wales would be attributable to the power lines and even this figure has considerable statistical uncertainty.

The study does arrive at a result that can’t be explained, and so it is reasonable to call for more work to be done. Nevertheless, the headline and article seem a little scare-mongering.

Comments

[latibulum]

I have often wondered about the generation of EMR from these lines, of course the wavelength is enormous, and I don't know how long a stretch of line would have to be in order to propagate a wave; 1/4 lamda I would think.

[Blue State]

Don't be so quick to shoot the messenger. The opening paragraphs that you quote, and call a "sensationalist story", is in fact an accurate summation of the results of the paper itself.

And I quote:

"Results: Compared with those who lived > 600 m from a line at birth, children who lived within 200 m had a relative risk of leukaemia of 1.69 (95% confidence interval 1.13 to 2.53); those born between 200 and 600 m had a relative risk of 1.23 (1.02 to 1.49). There was a significant (P < 0.01) trend in risk in relation to the reciprocal of distance from the line. No excess risk in relation to proximity to lines was found for other childhood cancers."

Even the headline, that there is a link, is also the conclusion of the paper.

Quoting again: "Conclusions: There is an association between childhood leukaemia and proximity of home address at birth to high voltage power lines, and the apparent risk extends to a greater distance than would have been expected from previous studies."

Skeptico, what is indisputable here is that the media story is no more "sensationalist" than the research report itself.

Also in Guardian Life is a leader headlined 'living with risks' which makes the same point as you, Skeptico: 'It looks like an eye-grabbing statistic... But it must be handled with extreme care.'

A quote from that article:

'The problem, however, is that the existence of even such relatively small differences can be enough to set off vigorous protest movements. This is in spite of the warnings of attaching too much significance to the findings - as the BMJ article suggests, it is as likely that other factors may have caused the higher incidence of leukemia. "Before activists begin blowing up power pylons, a bit of perspective might help," Dr Watts notes.'

[Skeptico]

I hadn’t seen that later Guardian article – thanks for pointing it out. You can read it here.

[rufus]

Blue State:

What is at all sensational about the paragraph you quoted? Perhaps you misunderstand the statistical use of the term "significant"?

That said, I actually think that your point is true as often as it's not. Public Health type work tends to be at least as much about politics as it is about science,
and the two aren't always a good match.

[Blue State]

I didn't say it was sensational. I said the article quoted by Skeptico was accurately paraphrasing the results published in the paper.

The article said: "Those living within 200 metres of the overhead cables were 70% more likely to develop the disease than similar children living more than 600 metres away."

The study said: "Compared with those who lived > 600 m from a line at birth, children who lived within 200 m had a relative risk of leukaemia of 1.69".

Skeptico called the article "sensationalist" and "scare mongering". He presumes that the story is a media beat-up, and those willing to read "the actual study", would find different conclusions.

That's flatly contradicted by the evidence, which shows the report was a straight treatment of the resulst and conclusion, and therefore no more sensationalist than the study itself.