Health effects of static magnetic fields--a review of the epidemiological evidence

Potential health effects of static magnetic fields have received far less attention than, for example, power frequency or radiofrequency fields. Static fields are found in certain occupational settings, e.g. in the aluminium and chloralkali industries, in arc-welding processes, and certain railways systems. Magnetic resonance imaging (MRI) for medical diagnosis is another source. This paper summarizes the epidemiological evidence of static magnetic field exposure and long-term health effects. There are only a few epidemiological studies available, and the majority of these have focused on cancer risks. There are some reports on reproductive outcomes, and sporadic studies of other outcomes. Overall, few occupational studies have focused specifically on effects of static magnetic field exposure, and exposure assessment have consequently been poor or non-existent. Results from studies that have estimated static magnetic field exposure have not indicated any increased cancer risks, but they are generally based on small numbers of cases and crude exposure assessment. Control of confounding has been limited, and it is likely that the “healthy worker” effect have influenced the results. A few studies have reported results on reproductive outcomes among aluminium workers and MRI operators, but limitations in study designs prevent conclusions. A problem in epidemiological studies of static magnetic fields is that workers in exposed occupations are also exposed to a wide variety of other potentially harmful agents, including some known carcinogens. In conclusion, the available evidence from epidemiological studies is not sufficient to draw any conclusions about potential health effects of static magnetic field exposure.     

A clinical look at the problem of drugs in pregnancy and their effect on the fetus.

The first annual W. E. Upjohn Lecture concerned itself with the interrelationship between administration of drugs to the pregnant woman and fetal outcome. The epidemiology of drug intake (both prescribed and self-administered drugs) during pregnancy is reviewed, using data derived from several surveys conducted both in the United States and in Scotland. The complexities of establishing a causal relationship between drug intake during pregnancy and effects upon the fetus are considered. Special emphasis is given to the adverse effects of aspirin and cigarette smoking. The shortage of data is critical and the need for further research is stressed.     

Present and future magnetic resonance sources of exposure to static fields

This paper considers the exposure of humans to static magnetic fields due to magnetic resonance imaging (MRI) procedures. It briefly introduces the types of magnetic fields associated with MRI. It then discusses trends in the number of people exposed to MRI, the field strength of the magnets used in MRI, and the types of applications of MRI. It also considers the types of staff who are exposed to magnetic fields due to MRI, and the alternative techniques that would be used in the absence of MRI.     

Maternal Smoking during Pregnancy and Fetal Organ Growth: A Magnetic Resonance Imaging Study

Objective

To study whether maternal cigarette smoking during pregnancy is associated with alterations in the growth of fetal lungs, kidneys, liver, brain, and placenta.

Design

A case-control study, with operators performing the image analysis blinded.

Setting

Study performed on a research-dedicated magnetic resonance imaging (MRI) scanner (1.5 T) with participants recruited from a large teaching hospital in the United Kingdom.

Participants

A total of 26 pregnant women (13 current smokers, 13 non smokers) were recruited; 18 women (10 current smokers, 8 nonsmokers) returned for the second scan later in their pregnancy.

Methods

Each fetus was scanned with MRI at 22–27 weeks and 33–38 weeks gestational age (GA).

Main outcome measures

Images obtained with MRI were used to measure volumes of the fetal brain, kidneys, lungs, liver and overall fetal size, as well as placental volumes.

Results

Exposed fetuses showed lower brain volumes, kidney volumes, and total fetal volumes, with this effect being greater at visit 2 than at visit 1 for brain and kidney volumes, and greater at visit 1 than at visit 2 for total fetal volume. Exposed fetuses also demonstrated lower lung volume and placental volume, and this effect was similar at both visits. No difference was found between the exposed and nonexposed fetuses with regards to liver volume.

Conclusion

Magnetic resonance imaging has been used to show that maternal smoking is associated with reduced growth of fetal brain, lung and kidney; this effect persists even when the volumes are corrected for maternal education, gestational age, and fetal sex. As expected, the fetuses exposed to maternal smoking are smaller in size. Similarly, placental volumes are smaller in smoking versus nonsmoking pregnant women.     

Comparison of residential power-frequency magnetic fields away from appliances in different countries

The purpose of this paper is to review measurements of residential power-frequency magnetic fields made in different countries and to determine whether average magnetic fields away from appliances are higher in some countries than in others. The paper includes 27 studies reporting measurements of residential magnetic fields in samples of homes: 14 from North America, 5 from the United Kingdom, and 8 from other European countries. Various factors that might make the results from individual studies unrepresentative of average fields in the relevant country are identified and discussed. Because distributions of magnetic fields generally are approximately log-normal, they are summarised by their geometric means. The best estimate of the geometric means of long-term average background fields in the United States is 60-70 nT and in the United Kingdom approximately 36-39 nT. In other countries, there are insufficient studies to draw firm conclusions on average fields. Measurements of personal exposure are higher than measurements of background fields, perhaps because they include exposures from appliances and other sources in the home. The ratio of personal exposure to background field seems, on average, to be approximately 1.4.     

The effects of continuous exposure to 20-kHz sawtooth magnetic fields on the litters of CD-1 mice.

Mated CD-1 mice were exposed to 20-kHz sawtooth magnetic fields similar to those associated with video display terminals (VDT). Four groups of animals were continuously exposed from day 1 to day 18 of pregnancy to field strengths of 0, 3.6, 17, or 200 microT. There were no less than 185 mated dams in each exposure group. On day 18, the dams were sacrificed and assessed for weight gain and pregnancy. The litters were evaluated for numbers of implantations, fetal deaths and resorptions, gross external, visceral and skeletal malformations, and fetal weights. There were no less than 140 pregnant females in each group, and there were no significant differences between any of the exposure groups and the sham group (0 microT) for any of the end points. The results of this study do not support the hypothesis that the 20-kHz VLF magnetic fields associated with video display terminals are teratogenic in mammals.     

Potentialities of magnetic resonance imaging in the complex of prenatal radiation diagnosis of fetal malformations

The purpose of the study was to investigate the potentialities of magnetic resonance imaging (MRI) in the complex of prenatal radiation diagnosis of fetal malformations. Twenty-eight female patients with suspected fetal malformations were examined. Ultrasound study was supplemented by MRI according to a specially developed protocol. Various fetal CNS malformations were diagnosed. These included the Arnold-Chiari syndrome, the Dandy-Walker syndrome, occlusive hydrocephaly, lobular holoprosencephaly, porencephaly, diaphragmatic hernias, anomalies of the abdomen and retroperitoneal space, as well as anomalies of facial structures, including median clefts, and dacryocystocele. The use of MRI in the complex prenatal radiation diagnosis makes it possible to visualize fetal malformation more clearly, contributes to the more adequate prediction of the outcome of pregnancy and to the choice of a management policy for a female patient.     

Effects of Gestational Magnetic Resonance Imaging on Methylation Status of Leptin Promoter in the Placenta and Cord Blood

Over the past two decades, magnetic resonance imaging (MRI) has been widely used for diagnosis in gestational women. Though it has several advantages, animal and human studies on the safety of MRI for the fetus remain inconclusive. Epigenetic modifications, which are crucial for cellular functioning, are prone to being affected by environmental changes. Therefore, we hypothesized that MRI during gestation may cause epigenetic modification alterations. Here, we investigated DNA methylation patterns of leptin promoter in the placenta and cord blood of women exposed to MRI during gestation. Results showed that average methylation levels of leptin in the placenta and cord blood were not affected by MRI. We also found that the methylation levels in the placenta and cord blood were not affected by different magnetic fields (1.5T and 3.0T MRI). However, if pregnant women were exposed to MRI at 15 to 20 weeks of gestation, the methylation level of leptin in cord blood was visibly lower than that of pregnant women exposed to MRI after 20-weeks of gestation (P = 0.037). mRNA expression level of leptin in cord blood was also altered, though mRNA expression of leptin in the placenta was not significantly affected. Therefore, we concluded that gestational MRI may not have major effects on the methylation level of leptin in cord blood and the placenta except for MRI applied before 20 weeks of gestation.     

Rapporteur report: implications for exposure guidelines

There is a paucity of information regarding the long-term health effects associated with exposure to static magnetic fields. Perceptual and other acute effects have been demonstrated above a threshold of about 2 T, and these form the basis for human exposure standards at present. Exposures well above this threshold are increasingly becoming more common as the technology associated with magnetic resonance imaging advances. Therefore, priority should be given to assessing the health risks associated with exposures to such fields. Studies should include a prospective cohort study investigating cancer risks of workers and patients exposed to fields in excess of 2 T, a study investigating effects on human cognitive performance from repeated exposures, and a molecular biology study investigating acute changes in genomic responses in volunteers exposed to fields of up to 8 T. Studies investigating the effects of long-term exposure on cancer, and on neurobehavioural development are also recommended using animals, where the use of transgenic models is encouraged. In addition, dosimetric studies should be conducted using high-resolution male, female and pregnant voxel phantoms, as should theoretical studies investigating the local currents induced in the eye and in the heart by movement during exposure. Finally, studies are recommended to investigate further the ability of static magnetic fields to significantly affect radical pair reactions in biological systems.     

Employee Attitudes about the Impact of Visitation Dogs on a College Campus

Therapy and visitation dogs are becoming more common on college campuses to provide comfort and support to students, but little attention has been given to the concerns of faculty and staff who share space with the dogs in their workplaces. The purpose of this study was to assess the perceptions of faculty and staff with regard to both the benefits and the hazards (e.g., dander, bites, fleas) and risks associated with the presence of visitation dogs in their workplaces. One hundred and thirty-eight employees who worked in buildings with resident visitation dogs completed an online survey about their perceptions of the hazards and risks of the dogs and the effects of dogs on the wellbeing of both students and employees. In general, employees perceived that the dogs presented minimal risks, and most employees believed that they can reduce stress and provide comfort to students on campus. There were a few employees, however, who reported that the dogs did not improve the work environment and conferred no benefits to the staff or students. The findings of the present survey support the mostly positive attitudes that people have for dogs in the workplace, but they also highlight a potential challenge: accommodating individuals who believe very strongly that dogs do not belong in work environments.