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Biomedical subjects

Leeka Kheifets

Publications and source records attributed to Leeka Kheifets.

At least 19 recordsLinked to original sources
PubMed2007

Magnetic field exposure and prognostic factors in childhood leukemia.

We examined the association between magnetic field (MF) exposure and the presence of prognostic risk factors among 482 children diagnosed with acute lymphoblastic leukemia (ALL) between 1996 and 2001. Personal 24-h MF measurements were obtained for 412 children; 386 children were included in analyses. There were no trends seen between increasing exposure to MF and the presence of adverse clinical and tumor-specific prognostic factors. Our results suggest that exposure to MF is not associated with the presence of unfavorable cytogenetic abnormalities in leukemic blast cells or with clinical factors at the time of diagnosis that predict poor survival.

Adolescent↗
PubMed2007

Feasibility of future epidemiological studies on possible health effects of mobile phone base stations.

The increasing deployment of mobile communication base stations led to an increasing demand for epidemiological studies on possible health effects of radio frequency emissions. The methodological challenges of such studies have been critically evaluated by a panel of scientists in the fields of radiofrequency engineering/dosimetry and epidemiology. Strengths and weaknesses of previous studies have been identified. Dosimetric concepts and crucial aspects in exposure assessment were evaluated in terms of epidemiological studies on different types of outcomes. We conclude that in principle base station epidemiological studies are feasible. However, the exposure contributions from all relevant radio frequency sources have to be taken into account. The applied exposure assessment method should be piloted and validated. Short to medium term effects on physiology or health related quality of life are best investigated by cohort studies. For long term effects, groups with a potential for high exposure need to first be identified; for immediate effect, human laboratory studies are the preferred approach.

Cell Phone↗
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

Leukemia attributable to residential magnetic fields: results from analyses allowing for study biases.

Nearly every epidemiologic study of residential magnetic fields and childhood leukemia has exhibited a positive association. Nonetheless, because these studies suffer from various methodologic limitations and there is no known plausible mechanism of action, it remains uncertain as to how much, if any, of these associations are causal. Furthermore, because the observed associations are small and involve only the highest and most infrequent levels of exposure, it is believed that the public health impact of an effect would be small. We present some formal analyses of the impact of power-frequency residential magnetic-field exposure (as measured by attributable fractions), accounting for our uncertainties about study biases as well as uncertainties about exposure distribution. These analyses support the idea that the public health impact of residential fields is likely to be limited, but both no impact and a substantial impact remain possibilities in light of the available data.

Bayes Theorem↗
PubMed2006

Public health impact of extremely low-frequency electromagnetic fields.

INTRODUCTION: The association between exposure to extremely low-frequency electric and magnetic fields (ELF) and childhood leukemia has led to the classification of magnetic fields by the International Agency for Research on Cancer as a "possible human carcinogen." This association is regarded as the critical effect in risk assessment. Creating effective policy in light of widespread exposure and the undisputed value of safe, reliable, and economic electricity to society is difficult and requires estimates of the potential public health impact and associated uncertainties. OBJECTIVES: Although a causal relationship between magnetic fields and childhood leukemia has not been established, we present estimates of the possible pubic health impact using attributable fractions to provide a potentially useful input into policy analysis under different scenarios. METHODS: Using ELF exposure distributions from various countries and dose-response functions from two pooled analyses, we calculate country-specific and worldwide estimates of attributable fractions (AFs) and attributable cases. RESULTS: Even given a wide range of assumptions, we find that the AF remains < 10%, with point estimates ranging from < 1% to about 4%. For small countries with low exposure, the number of attributable cases is less than one extra case per year. Worldwide the range is from 100 to 2,400 cases possibly attributable to ELF exposure. CONCLUSION: The fraction of childhood leukemia cases possibly attributable to ELF exposure across the globe appears to be small. There remain, however, a number of uncertainties in these AF estimates, particularly in the exposure distributions.

Bayes Theorem↗
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

Selection bias and its implications for case-control studies: a case study of magnetic field exposure and childhood leukaemia.

Based on the epidemiological association between residential exposure to extremely low frequency-magnetic fields (ELF-MF) and childhood leukaemia, the International Agency for Research on Cancer classified ELF-MF as a possible human carcinogen. Since clear supportive laboratory evidence is lacking and biophysical plausibility of carcinogenicity of MFs is questioned, a causal relationship between childhood leukaemia and magnetic field exposure is not established. Among the alternative explanations, selection bias in epidemiological studies of MFs seems to be the most plausible hypothesis. In reviewing the epidemiological literature on ELF-MF exposure and childhood leukaemia, we found evidence both for and against the existence of selection bias. To evaluate the potential for selection bias, we examined the relationship of socioeconomic status to subject participation and exposure to MFs. We find that, often, reporting of selection processes in itself is biased and incomplete, making the interpretation and evaluation of a potential for bias difficult. However, if present, such a bias would have wide implications for case-control studies in general. We call for better reporting and for evaluation of the potential for selection bias in all case-control studies, as well as, for the development of novel methods in control selection and recruitment.

Case-Control Studies↗
PubMed2005

Childhood leukemia and EMF: review of the epidemiologic evidence.

All populations are exposed to varying degrees of electromagnetic fields (EMF); in this study we consider only extremely low frequency (ELF) and radio frequency (RF) fields. After the first study of ELF and childhood leukemia in 1979, intensive epidemiologic investigation has sought to shed light on the potential relation between EMF and childhood leukemia. Consistent associations from epidemiologic studies and two pooled analyses have been the basis for the classification of ELF as a possible carcinogen by the International Agency for Research on Cancer (IARC). The study of RF is still in its infancy and little is known about residential RF exposure or its potential effects on childhood leukemia. The purpose of this study, presented at the WHO Workshop on Sensitivity of Children to EMF in Istanbul, Turkey in June 2004, is to review and critically assess the epidemiologic evidence on EMF and childhood leukemia.

Bias↗
PubMed2005

Developing policy in the face of scientific uncertainty: interpreting 0.3 microT or 0.4 microT cutpoints from EMF epidemiologic studies.

There has been considerable scientific effort to understand the potential link between exposures to power-frequency electric and magnetic fields (EMF) and the occurrence of cancer and other diseases. The combination of widespread exposures, established biological effects from acute, high-level exposures, and the possibility of leukemia in children from low-level, chronic exposures has made it both necessary and difficult to develop consistent public health policies. In this article we review the basis of both numeric standards and precautionary-based approaches. While we believe that policies regarding EMF should indeed be precautionary, this does not require or imply adoption of numeric exposure standards. We argue that cutpoints from epidemiologic studies, which are arbitrarily chosen, should not be used as the basis for making exposure limits due to a number of uncertainties. Establishment of arbitrary numeric exposure limits undermines the value of both the science-based numeric EMF exposure standards for acute exposures and precautionary approaches. The World Health Organization's draft Precautionary Framework provides guidance for establishing appropriate public health policies for power-frequency EMF.

Child↗
PubMed2005

EMF and health.

Electric and magnetic fields are ubiquitous in the modern society, and concerns have been expressed regarding possible adverse effects of these exposures. This review covers epidemiologic research on health effects of exposures to static, extremely low-frequency (ELF), and radio frequency (RF) fields. Research on ELF fields has been performed for more than two decades, and the methodology and quality of studies have improved over time. Studies have consistently shown increased risk for childhood leukemia associated with ELF magnetic fields, whereas ELF fields most likely are not a risk factor for breast cancer and cardiovascular disease. There are still inadequate data for other outcomes. More recently, focus has shifted toward RF exposures from mobile telephony. There are no persuasive data suggesting a health risk, but this research field is still immature with regard to the quantity and quality of available data. This technology is constantly changing and there is a need for continued research on this issue. Almost no epidemiologic data are available for static fields.

Abortion, Spontaneous↗
PubMed2005

The sensitivity of children to electromagnetic fields.

In today's world, technologic developments bring social and economic benefits to large sections of society; however, the health consequences of these developments can be difficult to predict and manage. With rapid advances in electromagnetic field (EMF) technologies and communications, children are increasingly exposed to EMFs at earlier and earlier ages. Consistent epidemiologic evidence of an association between childhood leukemia and exposure to extremely low frequency (ELF) magnetic fields has led to their classification by the International Agency for Research on Cancer as a "possible human carcinogen." Concerns about the potential vulnerability of children to radio frequency (RF) fields have been raised because of the potentially greater susceptibility of their developing nervous systems; in addition, their brain tissue is more conductive, RF penetration is greater relative to head size, and they will have a longer lifetime of exposure than adults. To evaluate information relevant to children's sensitivity to both ELF and RF EMFs and to identify research needs, the World Health Organization held an expert workshop in Istanbul, Turkey, in June 2004. This article is based on discussions from the workshop and provides background information on the development of the embryo, fetus, and child, with particular attention to the developing brain; an outline of childhood susceptibility to environmental toxicants and childhood diseases implicated in EMF studies; and a review of childhood exposure to EMFs. It also includes an assessment of the potential susceptibility of children to EMFs and concludes with a recommendation for additional research and the development of precautionary policies in the face of scientific uncertainty.

Brain Neoplasms↗
PubMed2004

Occupational magnetic field exposure and myocardial infarction incidence.

BACKGROUND: Studies on healthy volunteers have seen reduced heart rate variability after exposure to extremely low-frequency electric and magnetic fields (EMF). Because reduced heart rate variability has been linked to cardiovascular disease risk, it has been hypothesized that exposure to EMF might increase the risk of cardiovascular disease. One epidemiologic study has shown increased mortality from cardiovascular conditions in utility workers with elevated exposure to magnetic fields, but several other epidemiologic studies have failed to confirm this result. We tested the hypothesis that occupational EMF exposure increases the risk of myocardial infarction in a large population-based case-control study of myocardial infarction, with detailed information on potential confounders. METHODS: We used data from the SHEEP study, which is a population-based case-control study of acute myocardial infarction in Stockholm. Occupational EMF exposure was based on job titles 1, 5, and 10 years before diagnosis. We used 2 approaches to classify exposure: first, specific individual job titles with presumed elevated EMF exposure, and second, classification of subjects according to a job-exposure matrix. RESULTS: We found no increased risk of myocardial infarction in subjects classified as having elevated EMF exposure. For the highest exposure category of > or = 0.3 microT according to the job-exposure matrix, the adjusted relative risk was = 0.57 (95% confidence interval = 0.36-0.89). CONCLUSIONS: The results of this study do not support the hypothesis that occupational EMF exposure increases the risk of myocardial infarction.

Acute Disease↗
PubMed2004

Epidemiology of health effects of radiofrequency exposure.

We have undertaken a comprehensive review of epidemiologic studies about the effects of radiofrequency fields (RFs) on human health in order to summarize the current state of knowledge, explain the methodologic issues that are involved, and aid in the planning of future studies. There have been a large number of occupational studies over several decades, particularly on cancer, cardiovascular disease, adverse reproductive outcome, and cataract, in relation to RF exposure. More recently, there have been studies of residential exposure, mainly from radio and television transmitters, and especially focusing on leukemia. There have also been studies of mobile telephone users, particularly on brain tumors and less often on other cancers and on symptoms. Results of these studies to date give no consistent or convincing evidence of a causal relation between RF exposure and any adverse health effect. On the other hand, the studies have too many deficiencies to rule out an association. A key concern across all studies is the quality of assessment of RF exposure. Despite the ubiquity of new technologies using RFs, little is known about population exposure from RF sources and even less about the relative importance of different sources. Other cautions are that mobile phone studies to date have been able to address only relatively short lag periods, that almost no data are available on the consequences of childhood exposure, and that published data largely concentrate on a small number of outcomes, especially brain tumor and leukemia.

Adult↗