Childhood leukaemia close to high-voltage power lines--the Geocap study, 2002-2007

Residential proximity to electromagnetic field sources and birth weight: Minimizing residual confounding using multiple imputation and propensity score matching

Studies have suggested that residential exposure to extremely low frequency (50 Hz) electromagnetic fields (ELF-EMF) from high voltage cables, overhead power lines, electricity substations or towers are associated with reduced birth weight and may be associated with adverse birth outcomes or even miscarriages. We previously conducted a study of 140,356 singleton live births between 2004 and 2008 in Northwest England, which suggested that close residential proximity (≤ 50 m) to ELF-EMF sources was associated with reduced average birth weight of 212 g (95%CI: -395 to -29 g) but not with statistically significant increased risks for other adverse perinatal outcomes. However, the cohort was limited by missing data for most potentially confounding variables including maternal smoking during pregnancy, which was only available for a small subgroup, while also residual confounding could not be excluded. This study, using the same cohort, was conducted to minimize the effects of these problems using multiple imputation to address missing data and propensity score matching to minimize residual confounding. Missing data were imputed using multiple imputation using chained equations to generate five datasets. For each dataset 115 exposed women (residing ≤ 50 m from a residential ELF-EMF source) were propensity score matched to 1150 unexposed women. After doubly robust confounder adjustment, close proximity to a residential ELF-EMF source remained associated with a reduction in birth weight of -116 g (95% confidence interval: -224:-7 g). No effect was found for proximity ≤ 100 m compared to women living further away. These results indicate that although the effect size was about half of the effect previously reported, close maternal residential proximity to sources of ELF-EMF remained associated with suboptimal fetal growth.

Residential distance at birth from overhead high-voltage powerlines: childhood cancer risk in Britain 1962-2008

Background:

We extend our previous study of childhood leukaemia and proximity to high-voltage powerlines by including more recent data and cases and controls from Scotland, by considering 132-kV powerlines as well as 275 and 400 kV and by looking at greater distances from the powerlines.

Methods:

Case–control study using 53 515 children from the National Registry of Childhood Tumours 1962–2008, matched controls, and calculated distances of mother's address at child's birth to powerlines at 132, 275, and 400 kV in England, Wales and Scotland.

Results:

Our previous finding of an excess risk for leukaemia at distances out to 600 m declines over time. Relative risk and 95% confidence interval for leukaemia, 0–199 m compared with>1000 m, all voltages: 1960s 4.50 (0.97–20.83), 2000s 0.71 (0.49–1.03), aggregate over whole period 1.12 (0.90–1.38). Increased risk, albeit less strong, may also be present for 132-kV lines. Increased risk does not extend beyond 600 m for lines of any voltage.

Conclusions:

A risk declining over time is unlikely to arise from any physical effect of the powerlines and is more likely to be the result of changing population characteristics among those living near powerlines.

Distance from residence to power line and risk of childhood leukemia: a population-based case-control study in Denmark

PURPOSE

Epidemiological studies have found an association between exposure to extremely low-frequency magnetic fields (ELF-MF) and childhood leukemia. In 2005, a large British study showed an association between proximity of residence to high-voltage power lines and the risk of childhood leukemia. The association extended beyond distances at which the 'power line'-induced magnetic fields exceed background levels, suggesting that the association was not explained by the magnetic field, but might be due to chance, bias, or other risk factors associated with proximity to power lines. Our aim was to conduct a comparable study in an independent setting (Denmark).

METHODS

We included 1,698 cases aged <15, diagnosed with leukemia during 1968-2006, from the Danish Cancer Registry and 3,396 controls randomly selected from the Danish childhood population and individually matched by gender and year of birth. We used geographical information systems to determine the distance between residence at birth and the nearest 132-400 kV overhead power line.

RESULTS

Odds ratios (ORs) were 0.76 [95 % confidence interval (CI) 0.40-1.45] for children who lived 0-199 m from the nearest power line and 0.92 (95 % CI 0.67-1.25) for those who lived 200-599 m away when compared with children who lived ≥600 m away. When restricting the analysis to 220 and 400 kV overhead power lines, the OR for children who lived 200-599 m from a power line was 1.76 (95 % CI 0.82-3.77) compared to children who lived ≥600 m away. However, chance is a likely explanation for this finding as the result was not significant, numbers were small, and there were no indications of an higher risk closer to the lines since no cases were observed within 200 m of these.

CONCLUSIONS

We found no higher risk of leukemia for children living 0-199 m or for children living 200-599 m of a 132-400 kV overhead power line. A slightly elevated OR for children living between 200 and 599 m of a 220-400 kV overhead power line is likely to be a chance finding.