Residential mobility and childhood leukemia
Amoon AT, Oksuzyan S, Crespi CM, Arah OA, Cockburn M, Vergara X, Kheifets L. Residential mobility and childhood leukemia. Environ Res. 2018 Mar 22;164:459-466. doi: 10.1016/j.envres.2018.03.016. [Epub ahead of print]
• Children who moved were older, had younger mothers, and lower SES.
• Non-movers showed stronger associations with EMF exposures and childhood leukemia.
• Adjustment for variables predicting mobility, save dwelling, did not alter results.
• Mobility does not appear to explain observed links between EMF and leukemia.
AIMS: Studies of environmental exposures and childhood leukemia studies do not usually account for residential mobility. Yet, in addition to being a potential risk factor, mobility can induce selection bias, confounding, or measurement error in such studies. Using data collected for California Powerline Study (CAPS), we attempt to disentangle the effect of mobility.
METHODS: We analyzed data from a population-based case-control study of childhood leukemia using cases who were born in California and diagnosed between 1988 and 2008 and birth certificate controls. We used stratified logistic regression, case-only analysis, and propensity-score adjustments to assess predictors of residential mobility between birth and diagnosis, and account for potential confounding due to residential mobility.
RESULTS: Children who moved tended to be older, lived in housing other than single-family homes, had younger mothers and fewer siblings, and were of lower socioeconomic status. Odds ratios for leukemia among non-movers living <50 meters (m) from a 200+ kilovolt line (OR: 1.62; 95% CI: 0.72-3.65) and for calculated fields ≥ 0.4 microTesla (OR: 1.71; 95% CI: 0.65-4.52) were slightly higher than previously reported overall results. Adjustments for propensity scores based on all variables predictive of mobility, including dwelling type, increased odds ratios for leukemia to 2.61 (95% CI: 1.76-3.86) for living < 50 m from a 200 + kilovolt line and to 1.98 (1.11-3.52) for calculated fields. Individual or propensity-score adjustments for all variables, except dwelling type, did not materially change the estimates of power line exposures on childhood leukemia.
CONCLUSION: The residential mobility of childhood leukemia cases varied by several sociodemographic characteristics, but not by the distance to the nearest power line or calculated magnetic fields. Mobility appears to be an unlikely explanation for the associations observed between power lines exposure and childhood leukemia.
Funding: This work was supported by the Electric Power Research Institute. Crespi was also partially supported by the National Cancer Institute at the National Institutes of Health (grant P30 CA16042). Vergara is an employee of the Electric Power Research Institute.
Occupational ELF-MF exposure and hematolymphopoietic cancers - Swiss National Cohort analysis and updated meta-analysis
Huss A, Spoerri A, Egger M, Kromhout H, Vermeulen R; Swiss National Cohort. Occupational extremely low frequency magnetic fields (ELF-MF) exposure and hematolymphopoietic cancers - Swiss National Cohort analysis and updated meta-analysis. Environ Res. 2018 Mar 24;164:467-474. doi: 10.1016/j.envres.2018.03.022.
• ELF-MF exposure may affect specific hematolymphopoietic malignancies rather than “all leukaemia”.
• We evaluated effects of occupational ELF-MF exposure on different types of hematolymphopoietic malignancies.
• We observed increased risks of AML if workers were exposed to higher levels and for a longer period of time.
• Risks were in line with meta-analysed findings of previous studies.
PURPOSE: Previous studies have examined risks of leukaemia and selected lymphoid malignancies in workers exposed to extremely low frequency magnetic fields (ELF-MF). Most studies evaluated hematolymphopoietic malignancies as a combined category, but some analyses suggested that effects may be contained to some specific leukaemia or lymphoma subtypes, with inconsistent results.
METHODS: We examined exposure to ELF-MF and mortality 1990-2008 from different types of hematolymphopoietic cancers in the Swiss National Cohort, using a job exposure matrix for occupations recorded at censuses 1990 and 2000. We analysed 3.1 million workers exposed at different levels to ELF-MF: ever-high, only-medium, only-low exposure using Cox proportional hazard models. We evaluated risk of death from acute myeloid leukaemia (AML), chronic myeloid leukaemia, lymphoid leukaemia, diffuse large B-cell lymphomas, follicular lymphoma, Waldenström's macroglobulinemia, multiple myeloma and Hodgkin lymphoma.
RESULTS: Mortality from hematolymphopoietic cancers was not associated with exposure to ELF-MF with the exception of an increase in ever-high exposed men of myeloid leukaemias (HR 1.31, 95% CI 1.02-1.67), and AML (HR 1.26, 95%CI 0.93-1.70). If workers had been high exposed during their vocational training and at both censuses, these HR increased to 2.24 (95%CI 0.91-5.53) and 2.75 (95%CI 1.11-6.83), respectively.
CONCLUSIONS:Our analysis provided no convincing evidence for an increased risk of death from a range of hematolymphopoietic cancers in workers exposed to high or medium levels of ELF magnetic fields. However, we observed an increased risk of acute myeloid leukaemia in workers exposed to high levels for a longer duration. Observed risks are in line with meta-analysed previous reports on ELF-MF exposure and AML risk, with a summary relative risk of 1.21 (95%CI 1.08-1.37).
Meta-analysis of extremely low frequency electromagnetic fields and cancer risk:
a pooled analysis of epidemiologic studies
Zhang Y, Lai J, Ruan G, Chen C, Wang DW. Meta-analysis of extremely low frequency electromagnetic fields and cancer risk: a pooled analysis of epidemiologic studies. Environ Int. 2015 Dec 15;88:36-43. doi: 10.1016/j.envint.2015.12.012.
• A significant association between ELF-EMF exposure and cancer risk was identified.
• Subgroup analysis revealed increased risk only in North America, especially in United States.
• However, the data from individual European country was contradicted with each other.
• Increased risk was only observed in residential exposure or interview-based surveys.
• Device measured studies obtained no significant association in overall effects.
Human-made electromagnetic fields (EMFs), such as nonionizing radiation, are classified into three categories: extremely low frequency fields (< 300 Hz) ....
Studies have suggested that extremely low frequency electromagnetic fields (ELF-EMF) may affect physiological functions in animal models. However, epidemiologic studies investigating the association of ELF-EMF with the susceptibility to cancer yield contradictory results.
In this comprehensive analysis, we conducted a search for case-control surveys regarding the associations of ELF-EMF and cancer susceptibility in electronic databases. A total of 42 studies involving 13,259 cases and 100,882 controls were retrieved.
All studies were case–control studies, including 23 breast cancer ..., 1 testicular cancer ..., 1 acoustic neuroma ..., 1 endometrial cancer ...., and 3 other cancer cases.
Overall, increased susceptibility to cancer was identified in the ELF-EMF exposed population (OR=1.08, 95% CI: 1.01, 1.15, P=0.02). In the stratified analyses, increased risk was found in North America (OR=1.10; 95% CI: 1.02, 1.20, P=0.02), especially the United States (OR=1.10; 95% CI: 1.01, 1.20, P=0.03). However, studies from Europe contradict these results. Moreover, a higher risk was found to be statistically significantly associated with the residential exposed population (OR=1.18; 95% CI: 1.02, 1.37, P=0.03). Furthermore, an increased cancer risk was found in interview-based surveys (OR=1.16; 95% CI: 1.00, 1.35, P=0.04). In device measurement-based studies, a slight increased risk was found only in premenopausal breast cancer (OR=1.23; 95% CI: 1.01, 1.49, P=0.04).
Our meta-analysis suggests that ELF-EMFs are associated with cancer risk, mainly in the United States and in residential exposed populations. Methodological challenges might explain the differences among studies.
The overall evaluation conducted by the World Health Organization (WHO) indicated that extremely low-frequency magnetic fields (ELF-EMFs) are possibly carcinogenic to humans (Group 2B), while static electric and magnetic fields and extremely low-frequency electric fields are not classifiable as to their carcinogenicity to humans (Group 3) (Humans, 2002).
ELF-EMFs are mainly generated by power transmission lines, power equipment or appliances (Chen et al., 2013). Because of the rapid development of industry and society, humans are surrounded by various electric devices, and exposure to ELF-EMFs is increasing. Currently, the biological effects induced by ELF-EMFs on human health have become a cause for concern (Grellier et al., 2014 and Zhang et al., 2015).
In general, animal experiments have produced positive results for all known human carcinogens, for which adequate testing has been performed (Humans, 2002). However, it is notable that childhood leukemia is the only cancer outcome for which this association has been consistently found using epidemiological methods (Grellier et al., 2014). It has been hypothesized that experiments designed following the classical two-step initiator–promoter concept of carcinogenesis may not be appropriate for understanding the biological effects of ELF-EMFs, as disease progression may result from complex interactions of genotoxic and non-genotoxic carcinogens (Juutilainen, 2008).
The results in Fig. 2 show that weak association between EMF-ELF exposure and susceptibility to cancer was identified when all the eligible studies were pooled (OR = 1.08, 95% CI: 1.01, 1.15, P = 0.02) regardless of the exposure models or cancer types (Fig. 2).
In the country subgroup analysis, a statistically significant increase in risk was found in North America (15 breast cancer, 3 brain cancer, 1 leukemia and 1 other cancer; OR = 1.10, 95% CI: 1.02, 1.20, P = 0.02), mainly in the United States (14 breast cancer, 3 brain cancer and 1 other cancer; OR = 1.10, 95% CI: 1.01, 1.20, P = 0.03). On the contrary, no statistically significant association between EMF-ELFs and cancer risk was found in a global analysis of European studies (7 breast cancer, 7 brain cancer, 8 leukemia and 5 other cancers) .... An increased risk of cancer was found in Norway (3 breast cancer, 1 brain cancer, 1 leukemia and 1 other cancer; OR = 1.11, 95% CI: 1.02, 1.21, P = 0.02) and France (1 brain cancer and 1 leukemia; OR = 1.38, 95% CI: 1.03, 1.84, P = 0.03), while a decreased risk was found in Sweden (4 breast cancer, 1 brain cancer, 1 leukemia and 1 other cancer; OR = 0.90, 95% CI: 0.84, 0.96, P = 0.001) and England (2 brain cancer, 2 leukemia and 2 other cancers; OR = 0.82, 95% CI: 0.69, 0.96, P = 0.02). In addition, a study from New Zealand also showed an increased cancer risk (1 leukemia; OR = 1.97, 95% CI: 1.08, 3.59, P = 0.03) .... Further subgroup analyses based on cancer type did not reveal any statistically significant associations in all of the analyzed types. When compared by exposure methods, an increased risk was only observed in residential exposure populations (OR = 1.18; 95% CI: 1.02, 1.37, P = 0.03).
[Note that the 23 studies that examined breast cancer risk yielded a marginally significant association with ELF-EMF exposure (OR = 1.07, p = .06)].
In conclusion, in our study, relevant literature selected from broad databases with stringent standards revealed an increased risk of cancer upon ELF-EMF exposure. However, more quantitative studies will contribute to more comprehensive results in the future.