Kheifets et al 2010 pooled analysis

Update to Ahlbom pooled analysis of magnetic fields and childhood leukaemia

The epidemiology of magnetic fields and childhood leukaemia is usually summarised by the Ahlbom et al pooled analysis from 2000, which combined the results from all the individual studies that met certain criteria.

Since then, further studies have been published.  A new pooled analysis, by Kheifets et al in 2010, looked at those more recent studies.  It concluded that the studies since 2000 broadly confirm the Ahlbom finding.

If all the studies are included, the results compared to Ahlbom look like this:

graph showing results

That suggests the association has got slightly weaker.  But one of the studies included, from Brazil, is believed to have a particular bias that may make its results less reliable.  If the Brazil study is excluded and all the remaining studies compared, this is the result:

graph showing result

Note that the more recent studies together have only about a third as many exposed subjects as the original Ahlbom analysis.  So they support rather than replace the original analysis.

British Journal of Cancer (2010) 103, 1128–1135.
Pooled analysis of recent studies on magnetic fields and childhood leukaemia
L Kheifets, A Ahlbom, C M Crespi, G Draper, J Hagihara, R M Lowenthal, G Mezei, S Oksuzyan, J Schüz, J Swanson, A Tittarelli, M Vinceti and V Wunsch Filho

Background:  Previous pooled analyses have reported an association between magnetic fields and childhood leukaemia. We present a pooled analysis based on primary data from studies on residential magnetic fields and childhood leukaemia published after 2000.

Methods:  Seven studies with a total of 10,865 cases and 12,853 controls were included. The main analysis focused on 24-h magnetic field measurements or calculated fields in residences.

Results:  In the combined results, risk increased with increase in exposure, but the estimates were imprecise. The odds ratios for exposure categories of 0.1–0.2 μT, 0.2–0.3 μT and 0.3 μT, compared with <0.1 μT, were 1.07 (95% CI 0.81–1.41), 1.16 (0.69–1.93) and 1.44 (0.88–2.36), respectively. Without the most influential study from Brazil, the odds ratios increased somewhat. An increasing trend was also suggested by a nonparametric analysis conducted using a generalised additive model.

Conclusions:  Our results are in line with previous pooled analyses showing an association between magnetic fields and childhood leukaemia. Overall, the association is weaker in the most recently conducted studies, but these studies are small and lack methodological improvements needed to resolve the apparent association. We conclude that recent studies on magnetic fields and childhood leukaemia do not alter the previous assessment that magnetic fields are possibly carcinogenic.