Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “MAGNETISM”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,765 records · Page 98Linked to original sources
PubMed1999

Reduced excretion of a melatonin metabolite in workers exposed to 60 Hz magnetic fields.

The effects of occupational 60 Hz magnetic field and ambient light exposures on the pineal hormone, melatonin, were studied in 142 male electric utility workers in Colorado, 1995-1996. Melatonin was assessed by radioimmunoassay of its metabolite, 6-hydroxymelatonin sulfate (6-OHMS), in post-work shift urine samples. Personal magnetic field and light exposures were measured over 3 consecutive days using EMDEX C meters adapted with light sensors. Two independent components of magnetic field exposure, intensity (geometric time weighted average) and temporal stability (standardized rate of change metric or RCMS), were analyzed for their effects on creatinine-adjusted 6-OHMS concentrations (6-OHMS/cr) after adjustment for age, month, and light exposure. Geometric mean magnetic field exposures were not associated with 6-OHMS/cr excretion. Men in the highest quartile of temporally stable magnetic field exposure had lower 6-OHMS/cr concentrations on the second and third days compared with those in the lowest quartile. Light exposure modified the magnetic field effect. A progressive decrease in mean 6-OHMS/cr concentrations in response to temporally stable magnetic fields was observed in subjects with low workplace light exposures (predominantly office workers), whereas those with high ambient light exposure showed negligible magnetic field effects. Melatonin suppression may be useful for understanding human biologic responses to magnetic field exposures.

Adult↗
PubMed1996

Estimating exposure in studies of residential magnetic fields and cancer: importance of short-term variability, time interval between diagnosis and measurement, and distance to power line.

Validity of exposure assessment methods has been a major concern in epidemiologic studies of magnetic field exposure and cancer. We conducted a study to evaluate the relative importance of distance to power lines and calculated historical magnetic fields when estimating past magnetic field exposure. Another goal was to compare results based on various estimates of magnetic field exposure, to assess the importance of short-term variability in magnetic fields, time between diagnosis and measurement, and sources of magnetic field exposure. We used data from a Swedish case-control study of residential exposure to magnetic fields and cancer. Childhood leukemia risk was associated with calculated historical annual average magnetic fields regardless of distance, and the association with distance disappeared when both variables were entered into the same logistic regression model. Relative risks for measurements at the time of the study (contemporary annual average fields, spot calculations, and spot measurements) were all close to or below unity. The results support the hypothesis that the difference between results using historical calculations and spot measurements is explained by the time interval between diagnosis and contemporary magnetic field estimates.

Adolescent↗
PubMed2002

A population-based prospective cohort study of personal exposure to magnetic fields during pregnancy and the risk of miscarriage.

To study the effect of magnetic fields on the risk of miscarriage, we conducted a population-based prospective cohort study among pregnant women within a large health maintenance organization. All women with a positive pregnancy test at less than 10 weeks of gestation and residing in the San Francisco area were contacted for participation in the study. We conducted in-person interviews to obtain information on risk factors for miscarriage and other potential confounders. All participants were also asked to wear a magnetic field-measuring meter for 24 hours and to keep a diary of their activities. Pregnancy outcomes were obtained for all participants by searching the health maintenance organization's databases, reviewing medical charts, and telephone follow-up. We used the Cox proportional hazard model for examining the magnetic field-miscarriage association. A total of 969 subjects were included in the final analyses. Although we did not observe an association between miscarriage risk and the average magnetic field level, miscarriage risk increased with an increasing level of maximum magnetic field exposure with a threshold around 16 milligauss (mG). The rate ratio (RR) associated with magnetic field exposure > or = 16 mG (vs <16 mG) was 1.8 [95% confidence interval (CI) = 1.2-2.7]. The risk remained elevated for levels (in tertiles) of maximum magnetic field exposure > or = 16 mG. The association was stronger for early miscarriages (<10 weeks of gestation) (RR = 2.2, 95% CI = 1.2-4.0) and among "susceptible" women with multiple prior fetal losses or subfertility (RR = 3.1, 95% CI = 1.3-7.7). After excluding women who indicated that their daily activity pattern during the measurements did not represent their typical daily activity during pregnancy, the association was strengthened; RR = 2.9 (95% CI = 1.6-5.3) for maximum magnetic field exposure > or = 16 mG, RR = 5.7 (95% CI = 2.1-15.7) for early miscarriage, and RR = 4.0 (95% CI = 1.4-11.5) among the susceptible women. Our findings provide strong prospective evidence that prenatal maximum magnetic field exposure above a certain level (possibly around 16 mG) may be associated with miscarriage risk. This observed association is unlikely to be due to uncontrolled biases or unmeasured confounders.

Abortion, Spontaneous↗
PubMed1991

Technical and practical aspects of magnetic nerve stimulation.

Magnetic stimulators consist of a high-voltage (400 V to more than 3 kV), high-current (4 kA to more than 20 kA) discharge system producing a brief pulse of magnetic field (1-10 T lasting up to a few milliseconds). In order to ensure safety and reliability, care has to be taken in the construction of magnetic stimulators and especially their stimulating coils, which may come into contact with the patient, by the use of adequate mechanical and electrical insulation and the incorporation of sensors to monitor temperature, voltage, etc. Where possible, equipment should be manufactured to comply with safety standards such as UL504 and IEC601. The effectiveness of a magnetic stimulator depends on many parameters such as the maximization of the peak coil energy, fast magnetic field rise times, and good coil design. It is also important to choose a coil based on its intended clinical application and not simply on account of its high magnetic field strength. A small coil, producing a high surface magnetic field, is suitable in the stimulation of superficial nerves, whereas a larger coil, with a low magnetic field intensity, may well be more suitable for the stimulation of deep nerves. Double, figure-eight, or butterfly coils produce more localised induced currents allowing for more selective stimulation. The exposure of the brain to high magnetic field strengths can also be reduced by using larger coils.

Electric Conductivity↗
PubMed2006

A road map for creating a Magnet work environment.

OBJECTIVE: The authors examine the relationship between working environment and the developmental level of the workforce, against the backdrop of the American Nurses Credentialing Center Magnet Recognition Program, to provide a road map for creating a positive work environment. BACKGROUND: With the daily demands on nurse managers, there is a need to identify focused strategies to achieve a Magnetized, high-performing work environment. METHODS: The American Nursing Association Magnet survey was administered to nurses at a large healthcare system. Patient units at each hospital were categorized as reactive, responsive, proactive, or high performing. Similar categories of units across all 6 hospitals were analyzed. Analysis of variance was performed on each Force of Magnetism by developmental level. RESULTS: Mean scores measuring the Forces of Magnetism were statistically significant between reactive and responsive units. Likewise, mean scores between responsive and proactive units were also statistically significant. Between reactive and responsive units, there were 3 statistically significant forces of Magnetism: organizational structure, management style, and interdisciplinary relations. These are labeled primary priority forces. Between responsive and proactive units, there were 6 statistically significant forces of Magnetism labeled secondary priority forces: policies and programs; professional models of care; quality of care; consultation and resources; autonomy; and interdisciplinary relations. CONCLUSIONS: Nursing staff perceive the "Magnetism" of the work environment differently, depending on the developmental level of the unit. Nurse managers with reactive units should focus on the 3 Forces of Magnetism identified as the primary priority forces, in order to help develop their unit to the next level of responsive. Once a responsive level has been achieved, the next 6 forces should be addressed.

Data Collection↗
PubMed2002

Shielding, but not zeroing of the ambient magnetic field reduces stress-induced analgesia in mice.

Magnetic field exposure was consistently found to affect pain inhibition (i.e. analgesia). Recently, we showed that an extreme reduction of the ambient magnetic and electric environment, by mu-metal shielding, also affected stress-induced analgesia (SIA) in C57 mice. Using CD1 mice, we report here the same findings from replication studies performed independently in Pisa, Italy and London, ON, Canada. Also, neither selective vector nulling of the static component of the ambient magnetic field with Helmholtz coils, nor copper shielding of only the ambient electric field, affected SIA in mice. We further show that a pre-stress exposure to the mu-metal box is necessary for the anti-analgesic effects to occur. The differential effects of the two near-zero magnetic conditions may depend on the elimination (obtained only by mu-metal shielding) of the extremely weak time-varying component of the magnetic environment. This would provide the first direct and repeatable evidence for a behavioural and physiological effect of very weak time-varying magnetic fields, suggesting the existence of a very sensitive magnetic discrimination in the endogenous mechanisms that underlie SIA. This has important implications for other reported effects of exposures to very weak magnetic fields and for the theoretical work that considers the mechanisms underlying the biological detection of weak magnetic fields.

Analgesia↗
PubMed2006

Magnetic coupling of waves and oscillations in the lower solar atmosphere: can the tail wag the dog?

Can the ubiquitously magnetic solar atmosphere have any effect on solar global oscillations? Traditionally, solar atmospheric magnetic fields are considered to be somewhat less important for the existence and characteristic features of solar global oscillations (p,f and the not-yet-observed g-modes). In this paper, I demonstrate the importance of the presence of magnetism and plasma dynamics for global resonant oscillations in the solar atmosphere. In particular, in the lower part of the solar atmosphere there are both coherent and random components of magnetic fields and velocity fields, each of which contribute on its own to the line widths and frequency variations of solar global acoustic waves. Changes in the coherent large-scale atmospheric magnetic fields cause frequency shifts of global oscillations over a solar cycle. The random character of the continuously emerging, more localized, magnetic carpet (i.e. small-scale, possibly even sub-resolution, loops) gives rise to additional frequency shifts. On the other hand, random and organized surface and sub-surface flows, like surface granulation, meridional flows or differential rotation, also affect the coupling mechanism of global oscillations to the lower magnetic atmosphere. The competition between magnetic fields and flows is inevitable. Finally, I shall discuss how solar global oscillations can resonantly interact with the overlaying inhomogeneous lower solar atmosphere embedded in a magnetic carpet. Line width broadening and distorsion of global acoustic modes will be discussed. The latter is suggested to be tested and measured by using ring-analysis techniques.

Journal Article↗
PubMed1999

Statistical mechanics of nonrelativistic charged particles in a constant magnetic field.

The statistical mechanics of a system of nonrelativistic charged particles in a constant magnetic field is discussed. The spatial dimension D is arbitrary, with D>or=3 assumed. Calculations are presented from first principles using the effective action method. For D>or=5 the system has a phase transition with a Bose condensate. We show how the effective action method deals in a very natural way with the condensate, and study its role in the magnetization of the gas. For large values of the magnetic field we show how the magnetized gas in D spatial dimensions behaves like the free Bose gas in D-2 spatial dimensions. Even though for D=3 the magnetized gas does not have a phase transition for any nonzero value of the magnetic field, we show how the specific heat starts to resemble the result for the free gas as the magnetic field is reduced. A number of analytical approximations for the magnetization and specific heat are given, and compared with numerical results. In this way we are able to study in precise detail how the B-->0 limit of the magnetized gas is achieved.

Journal Article↗
PubMed2001

Stability of modulated-gravity-induced thermal convection in magnetic fields.

A stability analysis is presented of modulated-gravity-induced thermal convection in a heated fluid layer subject to an applied magnetic field. The nearest correction to the critical Rayleigh number for both single and multiple frequency oscillating-gravity components is obtained by solving the linearized magnetohydrodynamic equations using the small parameter perturbation technique. The correction depends on both the applied magnetic field and the oscillating frequency. In the absence of an applied magnetic field, the correction depends on the Prandtl number only when the exciting frequency is small. However, it asymptotically approaches zero as the frequency increases, with or without the presence of a magnetic field. The heated fluid layer is more stable with gravity modulation than with any type of wall temperature modulation. The difference becomes smaller with decreasing Prandtl number Pr. This finding is of critical importance in that ground-based experiments with appropriate wall temperature modulations may be conducted to simulate the oscillating-gravity effects on the onset of thermal convection in lower-Prandtl-number fluids. For conducting melts considered for microgravity applications, it is possible to apply an external magnetic field to further inhibit the onset of modulated-gravity-induced thermal convection. This effectiveness increases with the Hartmann number Ha. For large Ha, the nearest correction term R02 approximately Ha2 as the magnetic Prandtl number Pm<<1. However, R02 approximately Ha(4/3) for Ha>>1 and Pm>>1, provided that Ha<0.5pi(Pm/Pr(3/2)), which is satisfied by a majority of space melt experiments. Thus, under normal laboratory conditions applied magnetic fields are more effective in stabilizing a conducting fluid subject to an oscillating-gravity field than one subject to a constant field. If Ha>0.5pi(Pm/Pr(3/2)), R02 approximately -Ha2 for Ha>>1 and Pm>>1 and the magnetic field becomes less effective in stabilizing thermal convection driven by oscillating gravity than that driven by the constant gravity. This is in contrast with the existing studies on thermal convection stability in a magnetic field, which show that marginal stability is independent of Pm and always increases with increasing applied field.

Journal Article↗
PubMed2003

Initial susceptibility, flow curves, and magneto-optics of inverse magnetic fluids.

We introduce inverse magnetic fluids, consisting of gibbsite [Al(OH)(3)] platelets and alumina (Al2O3) spheres dispersed in a magnetic fluid, studied together with silica (SiO2) dispersions based on the same magnetic fluid matrix. Atomic force microscopy, optical microscopy, and alternate gradient magnetometry confirm the remarkable stability of the samples. Optical microscopy shows aggregation of nonmagnetic spheres, which, surprisingly, strongly depends on the concentration of the magnetic fluid rather than the concentration of nonmagnetic particles. Our model for the initial susceptibility of inverse magnetic fluids agrees very well with experimental data for systems containing spherical particles. The flow curves in an external magnetic field are strongly influenced by the aggregation of nonmagnetic particles or preformed nonmagnetic particle clusters, and by their disruption due to the shear flow. Static linear magnetobirefringence and magnetodichroism of all samples are investigated both experimentally and theoretically. These effects, which occur in all magnetic fluids, can be enhanced by the additional anisotropy due to the magnetic holes. The experiments we performed showed that, at a wavelength of 820 nm, the magnetodichroism is increased while the magneto-birefringence decreases when nonmagnetic particles were dispersed in the magnetic fluid. Magneto-birefringence is expected to be increased at large enough wavelengths only.

Journal Article↗
PubMed2003

Magnetic X-ray absorption fine structure for Ni-Mn alloys.

Magnetic X-ray absorption fine-structure (XAFS) spectra have been measured for Ni-Mn alloys. The magnetic XAFS in the near-edge region (X-ray absorption near-edge structure, XANES) and X-ray magnetic circular dichroism (XMCD) of the Mn and Ni K-edge for Ni(1-x)Mn(x) (x = 0.25, 0.24 and 0.20) show that (i) the local magnetic structure around the Mn atom is quite different from that around the Ni atom, and (ii) the peak intensity in the magnetic XANES of the Mn K-edge depends on the magnetization of the sample in contrast to the Ni K-edge. The Mn K-edge magnetic EXAFS (extended XAFS) for Ni(0.76)Mn(0.24) is also measured. The second and fourth peaks in the Fourier transform are observed to be enhanced in comparison with the non-magnetic EXAFS, indicating that the second- and fourth-shell Ni atoms are replaced by Mn atoms due to heat treatment (atomic ordering). Semi-relativistic theoretical calculation explains the observed magnetic EXAFS.

Journal Article↗
PubMed1996

Magnetic orientation in birds

The magnetic field of the earth is an omnipresent, reliable source of orientational information. A magnetic compass has been demonstrated in 18 species of migrating birds. In all species studied with regard to its functional properties, it was found to be an 'inclination compass', i.e. the birds derive directional information from the inclination of the field lines, and thus distinguish between 'poleward' and 'equatorward' rather than 'north' and 'south'. Such a mechanism means that birds from the northern and southern hemisphere may rely on the same migratory programme. Long-distance migrants, however, face the problem that their magnetic compass gives bimodal information at the magnetic equator. Transfers of information between the magnetic field and celestial sources of directional information have been demonstrated; the two systems interact in a complex way. The data on the use of magnetic parameters for position finding are less clear. The experiments involve releases of homing pigeons; correlations of their orientation with natural variations in the magnetic field and the effects of magnetic manipulation reveal an enormous variability. The role of magnetic parameters in the multifactorial navigational system is poorly understood.

Journal Article↗
PubMed1999

The case for light-dependent magnetic orientation in animals

Light-dependent models of magnetoreception have been proposed which involve an interaction between the magnetic field and either magnetite particles located within a photoreceptor or excited states of photopigment molecules. Consistent with a photoreceptor-based magnetic compass mechanism, magnetic orientation responses in salamanders, flies and birds have been shown to be affected by the wavelength of light. In birds and flies, it is unclear whether the effects of light on magnetic orientation are due to a direct effect on a magnetoreception system or to a nonspecific (e.g. motivational) effect of light on orientation behavior. Evidence from shoreward-orienting salamanders, however, demonstrates that salamanders perceive a 90 degrees counterclockwise shift in the direction of the magnetic field under long-wavelength (>=500 nm) light. A simple physiological model based on the antagonistic interaction between two magnetically sensitive spectral mechanisms suggests one possible way in which the wavelength-dependent effects of light on the salamander's magnetic compass response might arise. Assuming that the wavelength-dependent characteristics of the avian magnetic response can be attributed to an underlying magnetoreception system, we discuss several hypotheses attempting to resolve the differences observed in the wavelength-dependent effects of light on magnetic orientation in birds and salamanders. By considering the evidence in the context of photoreceptor- and non-photoreceptor-based mechanisms for magnetoreception, we hope to encourage future studies designed to distinguish between alternative hypotheses concerning the influence of light on magnetoreception.

Journal Article↗
PubMed2004

Magnetic-field-induced DNA strand breaks in brain cells of the rat.

In previous research, we found that rats acutely (2 hr) exposed to a 60-Hz sinusoidal magnetic field at intensities of 0.1-0.5 millitesla (mT) showed increases in DNA single- and double-strand breaks in their brain cells. Further research showed that these effects could be blocked by pretreating the rats with the free radical scavengers melatonin and N-tert-butyl-alpha-phenylnitrone, suggesting the involvement of free radicals. In the present study, effects of magnetic field exposure on brain cell DNA in the rat were further investigated. Exposure to a 60-Hz magnetic field at 0.01 mT for 24 hr caused a significant increase in DNA single- and double-strand breaks. Prolonging the exposure to 48 hr caused a larger increase. This indicates that the effect is cumulative. In addition, treatment with Trolox (a vitamin E analog) or 7-nitroindazole (a nitric oxide synthase inhibitor) blocked magnetic-field-induced DNA strand breaks. These data further support a role of free radicals on the effects of magnetic fields. Treatment with the iron chelator deferiprone also blocked the effects of magnetic fields on brain cell DNA, suggesting the involvement of iron. Acute magnetic field exposure increased apoptosis and necrosis of brain cells in the rat. We hypothesize that exposure to a 60-Hz magnetic field initiates an iron-mediated process (e.g., the Fenton reaction) that increases free radical formation in brain cells, leading to DNA strand breaks and cell death. This hypothesis could have an important implication for the possible health effects associated with exposure to extremely low-frequency magnetic fields in the public and occupational environments.

Animals↗
PubMed2002

The effect of melatonin on morphological changes in liver induced by magnetic field exposure in rats.

In this study, we aimed to investigate the possible effect of melatonin on morphological changes in liver induced by magnetic fields exposure. Thirty albino young male Wistar Albino rats were used in the study. They were divided into 3 groups. Control group (C) (n: 10) received daily intraperitoneal injections of saline (0.1 ml/100 g) containing 5% ethanol for two weeks. Only magnetic field exposed (MF) group (n: 10); only magnetic field exposed had daily intraperitoneal injections of physiologic saline (0.1 ml/100 g) containing 5% ethanol for two weeks. Magnetic field exposed and melatonin treated (MF+m) group (n: 10); melatonin was dissolved in ethanol with further dilution in physiological saline. The animals in this group were exposed magnetic fields for two weeks. The magnetic fields exposed animals had intraperitoneal single dose of 4 mg/kg melatonin (0.1 ml/100 g) at 10:00 o'clock daily for two weeks following magnetic fields exposure. We used commercial CB handheld portable transceiver, Midland (USA) labelled, of 4 Watts, 40 channel. This channel frequency has been measured 27.17 MHz with frequency counter. According to the IRPA exposure standards; for 27 MHz, for 6 min, exposure limit is 0.2 mW/cm2. This value is for General Public. For occupational exposure limit is 1 mW/cm2. We have to consider General Public exposure limit. Therefore our limit is 0.2 mW/cm2. In other words; in this study; our exposure is always over the recommended limit. All the animals were decapitated. Liver samples were fixed in buffered neutral formalin. Paraffin sections were dyed with hematoxylen-eosin. Sections were examined under light microscopy. In MF group; sinusoidal dilatations, mixed cell infiltrations noticed in the periportal area, necrosis and vacuoler degeneration were determined in liver samples. However, parenchymal and stromal structures were observed to be prevented partially from effects of magnetic fields in melatonin treated group. In conclusion, it is suggested that melatonin has a mild preventive effect on magnetic field exposed changes in liver tissue in the rats.

Animals↗
PubMed1993

Weak magnetic fields antagonize the effects of melatonin on blood glucose levels in Parkinson's disease.

Treatment with picoTesla magnetic fields recently has been reported to attenuate symptoms of Parkinson's disease (PD). The mechanisms by which weak magnetic fields ameliorate Parkinsonian symptoms are unknown. There is evidence that the pineal gland is a "magnetosensor" in the brain since in experimental animals exposure to external magnetic fields alters the firing rate of pineal cells and induces inhibition of melatonin secretion. Hence, the clinical effects of weak magnetic fields in PD likewise may involve the mediation of the pineal gland. Animal data indicate that the pineal gland is involved in the regulation of glucose metabolism and that exogenous administration of melatonin induces an hyperglycemic effect. To investigate the hypothesis that the pineal gland mediates the therapeutic properties of weak magnetic fields in PD, I studied the effects of orally administered melatonin (3.0 mg) followed by a 6 minute application of low intensity external weak magnetic fields (7.5 picoTesla) on blood glucose levels in two Parkinsonian patients. In both patients melatonin challenge produced a moderate hyperglycemic effect which was reversed by subsequent stimulation with weak magnetic fields. These findings support the hypothesis that weak magnetic fields inhibit melatonin secretion and that the antiParkinsonian properties of weak magnetic fields are mediated partially via the inhibition of melatonin secretion. Furthermore, these data suggest that melatonin receptor antagonists could be beneficial as an adjunctive treatment in PD and highlight the importance of the pineal-hypothalamic axis in the pathophysiology of the disease as well as in the mechanisms of action of antiParkinsonian drugs.

Aged↗
PubMed1999

Exposures of children in Canada to 60-Hz magnetic and electric fields.

OBJECTIVES: This study sought to characterize personal exposures of Canadian children to 60-Hz magnetic and electric fields and explain the variability. METHODS: Altogether 382 Canadian children up to 15 years of age wore meters recording 60-Hz electric and magnetic fields over 2 days. Meter location was noted. Thereafter, meters measured fields in the center of the children's bedrooms for 24 hours. Personal exposures were calculated for home, school or day care, outside the home, bedroom at night, and all categories combined (total). RESULTS: The arithmetic mean (AM) was 0.121 microT [geometric mean (GM): 0.085 microT), range 0.01-0.8 microT] for total magnetic fields. Fifteen percent of the total exposures exceeded 0.2 microT. The AM of the total electric fields was 14.4 (GM 12.3, range 0.82-64.7) V/m. By location category, the highest and lowest magnetic fields occurred at home during the day (0.142 microT) and during the night (0.112 microT), respectively. Measurements during sleep provided the highest correlation with total magnetic field exposure. Province of measurement explained 14.7% of the variation in the logarithms of total magnetic fields, and season accounted for an additional 1.5%. CONCLUSIONS: This study has identified differences in children's magnetic field exposures between provinces. Measurements at night provided the best surrogate for predicting total magnetic field exposure, followed by at-home exposure and 24-hour bedroom measurements. Electrical heating and air conditioning, wiring type, and type of housing appear to be promising indicators of magnetic field levels.

Canada↗
PubMed2002

[Evaluation of the effect of magnetic fields on the secretion of melatonin in humans and rats. Circadian study].

The consequences of electromagnetic exposure on human health are receiving increasing scientific attention and have become the subject of a vigorous public debate. In the present study we evaluated the effects of magnetic field on pineal function in man and rat. Two groups of Wistar male rats were exposed to 50-Hz magnetic fields of either 1, 10 or 100 microT. The first group was exposed for 12 hours and the second for 30 days (18 hours per day). Short-term exposure depressed both pineal NAT activity and nocturnal serum melatonin concentration but only with the highest intensity used (100 microT). Long-term exposure to a magnetic field significantly depressed the nighttime peak of serum melatonin concentration and pineal NAT activity with 10 and 100 microT. Our results show that sinusoidal magnetic fields altered the production of melatonin through an inhibition of pineal NAT activity. Both duration and intensity of exposure played an important role in this effect. In the second step of this study, thirty-two young men (20-30 years old) were divided into two groups (control group, i.e., sham-exposed: 16 subjects; exposed group: 16 subjects). The subjects were exposed to the magnetic field from 23 h to 08 h (i.e. for 9 h) while lying down. In one experiment the exposure was continuous, in the second one, the magnetic field was intermittent. No significant differences were observed between sham-exposed (control) and exposed men for serum melatonin and 6-sulfatoxymelatonin. In our last and more recent study, we looked for the circadian rhythm of melatonin in 15 men exposed chronically and daily for a period of 1-20 years, in the workplace and at home, to a 50 Hz (exposure 0.1 to > 0.3 microT) magnetic field. The results are compared to those for 15 unexposed men who served as controls. Blood samples were taken hourly from 2000 to 0800. Nighttime urine was also collected and analyzed. This work shows that subjects exposed over a long period (up to 20 years) and on a daily basis to magnetic fields experienced no changes in their plasma melatonin level, their urinary 6-sulfatoxymelatonin level, or the circadian rhythm of melatonin. It thus clearly rebuts the "melatonin hypothesis" that a decrease in plasma melatonin concentration--or a disruption in its secretion--explains the occurrence of, clinical disorders or cancers possibly related to magnetic fields.

Adult↗