Past experimental studies of rats exposed to electric or magnetic fields have found a diminution in melatonin secretion. The importance of the length of magnetic field exposure in this inhibitory effect suggests that the effect of these fields on pineal function may be cumulative, at least in rats. In fact, much of the evidence for the melatonin hypothesis is based on data for rodents. But humans and rodents differ with respect to melatonin secretion in two important ways: (1) rodents are nocturnally active, and they show differences in the anatomical location of the pineal gland; and (2) the geometry of the skull may cause stronger eddy currents in field-exposed animals.
Results about the effects of magnetic fields in higher mammals – lambs, monkeys and humans -- have heretofore been either negative or provide controversial results. Most work published thus far has involved the acute exposure of healthy volunteers to magnetic fields and has not found it to affect melatonin secretion. Nevertheless, it is possible that chronic human exposure to magnetic fields might affect melatonin secretion, its circadian rhythm, or both. Because of the obvious technical difficulties in exposing healthy volunteers to magnetic fields for a long period, at a high intensity, or both, the only feasible experimental approach toward the study of such chronic exposure involves the study of subjects exposed continually either on the job or at home -- occupationally or residentially.
A New Study
The possible effects of magnetic fields on human melatonin secretion is important from a public health perspective, because alterations in the secretion of this hormone (for example, phase shifting or reduced amplitude) are likely to lead to clinical disorders involving fatigue, sleep and mood disturbances, altered performance, and depression, all signs that can be related to desynchronization of circadian rhythms. Now, an innovative study addresses this issue. The methodology entails the examination of workers exposed to magnetic fields daily for 1 one to 20 years, both in the workplace and at home.
The authors of "Magnetic Fields and The Melatonin Hypothesis: A Study of Workers Chronically Exposed to 50-Hz Magnetic Fields" are Yvan Touitou, Françoise Camus, and Henriette Charbuy, from the Department of Biochemistry and Molecular Biology, Faculty of Medicine Pitié-Salpêtrière, and Jacques Lambrozo, Service des Etudes Médicales, Electricité de France/Gaz de France, all in Paris, France. Their findings appear in the June 2003 edition of the American Journal of Physiology – Regulatory, Integrative and Comparative Physiology.
Methodology
Thirty male volunteers (15 exposed and 15 controls) participated in the autumn study, when the light-dark cycle was 10 hours light-14 hours dark. All subjects had similar schedules, with daytime activity from 0700 to 2300 and nocturnal rest, and were similar in age and in physical activity. Subjects were required to have no acute or chronic diseases, have regular sleep habits, do no night work, have taken no trans-meridian airplane flights during the preceding two months, and take no drugs. All were nonsmokers who used alcohol and coffee in moderate quantities. The exposed workers had not been on call in the 48 hours preceding the experiment. They were asked not to use electric razors or hair dryers during the study or in the 24 hours before the blood samples were taken. Women were not included in this study because the interaction of their ovarian hormone cycle with melatonin secretion might have made the study results difficult to interpret.
The 15 test subjects all worked in extra high voltage (EHV) substations in the Paris metropolitan region, operating and maintaining the EHV electricity transmission network (225 and 400 KV). Their work essentially involved installing couplings between EHV lines as well as voltage transformers. The exposed subjects were also housed near the substations, which means that they were exposed to magnetic fields both while working and during their daily life in their lodgings. Ten of the 15 subjects were exposed from seven to 20 years, and five subjects were exposed from one to four years. The 15 control subjects did not work in a technical job that could have resulted in occupational exposure to magnetic fields. They were subjected only to the normal electromagnetic fields of our daily environment.
Dosimeters measured the exposure continuously for seven days, during the daytime and at night. Measurements were taken and recorded every 30 seconds all day long. Both exposed and control subjects wore the magnetic field recording device throughout the workday. At home, they placed it in a "public" room. The weekly geometric mean of individual exposures ranged from 0.1 to 2.6 µT. The results are compared with 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.
Results
The weekly geometric mean of individual exposures ranged from 0.1 to 2.6 µT. The arithmetic mean of the 15 exposure values was 0.72 µT. The arithmetic mean of daytime (workday) exposure of the 15 exposed subjects was 0.64 µT and nighttime (residential) exposure 0.82 µT. A subset of three subjects had a substantially higher exposure with an arithmetic mean of 2.10 µT. Their arithmetic mean workday exposure was 1.50 µT and nighttime residential exposure 2.71 µT. For the control subjects the weekly geometric mean of individual exposures ranged from 0.004 to 0.092 µT. The arithmetic mean of the 15 exposure values was 0.04 µT. The arithmetic mean of both the workday and nighttime exposure for the 15 controls was 0.04 µT.
A comparison between groups found that that melatonin secretion did not differ for the exposed and control groups.
Conclusions
This study of workers exposed daily to magnetic fields for a period of one to 20 years in their workplace and at home shows that this exposure does not lead to alterations in their melatonin secretion. The clinical signs (depression, mood and sleep disorders, malignant diseases, etc.) reported in some studies of people living or working near electric lines or substations thus do not appear to be associated with a disturbance in their melatonin levels.
It is possible that the difference in the effects observed in animals and humans is the result of both the anatomical configuration of the pineal gland and the principally nocturnal rhythm of rodent activity. A different sensitivity to magnetic fields between species could also be part of the explanation, as it is known that some species detect and perceive magnetic fields differently. It is also possible that some subjects are more sensitive to magnetic fields than others; this is very difficult to demonstrate in a case-control study because of the enormous interindividual variability of melatonin secretion and plasma melatonin concentrations in humans.
To the researchers' knowledge, this study is the first to examine both plasma melatonin circadian rhythm and urinary 6-sulfatoxymelatonin concentration in subjects who have been exposed chronically and for a long period to magnetic fields at home and at work. Therefore, it is the first research to show that chronic magnetic field exposure appears to have no cumulative effect in humans on serum melatonin secretion and circadian rhythm or urinary excretion of 6-sulfatoxymelatonin, at least among men in their forties.
Source: June 2003 edition of the American Journal of Physiology – Regulatory, Integrative and Comparative Physiology
The American Physiological Society (APS) was founded in 1887 to foster basic and applied science, much of it relating to human health. The Bethesda, MD-based Society has more than 10,000 members and publishes 3,800 articles in its 14 peer-reviewed journals every year.