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Biomedical subjects

John Swanson

Publications and source records attributed to John Swanson.

9 recordsLinked to original sources
PubMed2006

Childhood leukemia, electric and magnetic fields, and temporal trends.

During the past 25 years concern has been raised about the possible health effects of extremely low frequency (ELF) electric and magnetic fields (EMFs), particularly regarding childhood leukemia. Comparison of changes in electricity consumption (a surrogate for exposure) to changes in childhood-leukemia rates, known as ecologic correlation, have been used to argue both for and against the association between magnetic fields and childhood leukemia. In this paper we explore what can be learned from such an ecologic approach. We first examine separately the evidence on trends in exposure to EMFs and on trends in leukemia rates, and then compare the two. Both incidence rates and exposures have increased, but there are so many approximations and assumptions involved in connecting the two trends that we cannot regard the ecologic evidence as providing any meaningful evidence for or against a causal link.

Acute Disease↗
PubMed2006

Power-frequency electric and magnetic fields in the light of Draper et al. 2005.

Power-frequency electric and magnetic fields are produced wherever electricity is used; exposure is ubiquitous. Epidemiologic studies find an association between children living in homes with the highest magnetic fields and childhood leukemia, but bias is a possible alternative to a causal explanation. A new study, Draper et al., looks at residence close to high-voltage power lines, one source of exposure to such fields, and its design avoids any obvious bias. It finds elevated childhood leukemia rates, but extending too far from the power lines to be straightforwardly compatible with the existing literature. This leads to an examination of alternative explanations: magnetic fields, other physical factors, such as corona ions, the characteristics of the areas power lines pass through, bias, and chance. The conclusion is that there is currently no single preferred explanation, but that this is a serious body of science that needs further work until an explanation is found.

Electromagnetic Fields↗
PubMed2006

Biophysical mechanisms: a component in the weight of evidence for health effects of power-frequency electric and magnetic fields.

Comparatively high exposures to power-frequency electric and magnetic fields produce established biological effects that are explained by accepted mechanisms and that form the basis of exposure guidelines. Lower exposures to magnetic fields (< 1 microT average in the home) are classified as "possibly carcinogenic" on the basis of epidemiological studies of childhood leukemia. This classification takes into consideration largely negative laboratory data. Lack of biophysical mechanisms operating at such low levels also argues against causality. We survey around 20 biophysical mechanisms that have been proposed to explain effects at such low levels, with particular emphasis on plausibility: the principle that to produce biological effects, a mechanism must produce a "signal" larger than the "noise" that exists naturally. Some of the mechanisms are impossible, and some require specific conditions for which there is limited or no evidence as to their existence in a way that would make them relevant to human exposure. Others are predicted to become plausible above some level of field. We conclude that effects below 5 microT are implausible. At about 50 microT, no specific mechanism has been identified, but the basic problem of implausibility is removed. Above about 500 microT, there are established or likely effects from accepted mechanisms. The absence of a plausible biophysical mechanism at lower fields cannot be taken as proof that health effects of environmental electric and magnetic fields are impossible. Nevertheless, it is a relevant consideration in assessing the overall evidence on these fields.

Animals↗
PubMed2005

Childhood cancer in relation to distance from high voltage power lines in England and Wales: a case-control study.

OBJECTIVE: To determine whether there is an association between distance of home address at birth from high voltage power lines and the incidence of leukaemia and other cancers in children in England and Wales. DESIGN: Case-control study. SETTING: Cancer registry and National Grid records. SUBJECTS: Records of 29 081 children with cancer, including 9700 with leukaemia. Children were aged 0-14 years and born in England and Wales, 1962-95. Controls were individually matched for sex, approximate date of birth, and birth registration district. No active participation was required. MAIN OUTCOME MEASURES: Distance from home address at birth to the nearest high voltage overhead power line in existence at the time. 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. 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. About 4% of children in England and Wales live within 600 m of high voltage lines at birth. If the association is causal, about 1% of childhood leukaemia in England and Wales would be attributable to these lines, though this estimate has considerable statistical uncertainty. There is no accepted biological mechanism to explain the epidemiological results; indeed, the relation may be due to chance or confounding.

Adolescent↗
PubMed2002

A transmission utility's experience of applying EMF exposure standards.

Exposure standards for power-frequency electric and magnetic fields are often structured in terms of basic restrictions and investigation levels. For uniform exposures, investigation levels help the user operate within the standard without concern about exceeding the basic restriction. For non-uniform fields, however, numerical calculations of induced currents in the body may be necessary to determine compliance with the basic restriction. Utilities have strong incentives to apply exposure standards so that they do not impose unnecessary and unjustified constraints on their operations. They are therefore likely to be prepared to invest considerable effort in assessing compliance. However, the standards are based on round numbers, the values of tissue conductivity are not well characterized, and the calculations needed to apply the standards are still evolving. This suggests that, scientifically, this level of effort devoted to distinguishing compliant and non-compliant exposure scenarios is not justifiable.

Electromagnetic Fields↗