884
Electromagnetic fields: danger?
is there
a
SIR,-Dr Sibbison (July 14, p 106) comments on supposed hazards
electromagnetic fields. He cites Paul Brodeur’s articles as an example of "the enterprise of investigative reporters" on which "the average citizen must usually rely" for information about potential carcinogens. Three of these articles in New Yorker (and a book dealing with the same information) drew responses from scientists1.22 pointing out how Brodeur oversimplifies the evidence and ignores published work. It is unfortunate that misinformation on the alleged hazards of electromagnetic fields continues to be provided by the lay media when reports of reliable scientific studies in medical journals
from
available. Sibbison suggests that deletions were made from a draft report of the US Environmental Protection Agency (EPA) as a result of political pressure "because utilities executives might complain". In fact, most scientists familiar with this topic realise that (as the director of EPA’s Office of Health and Environmental Assessment has stated) the absence of both a mechanism of interaction and a dose-response relation do not support classification of an electromagnetic field as a "probable" carcinogen. By use of an evaluation process defmed by the International Agency for Research on Cancerinvestigators studying electromagnetic field effects have concluded that the limited and inconsistent data are insufficient to establish a causal association between exposure to electromagnetic fields and cancer. Sibbison also suggests that "front page headlines and segments on national television" were discouraged by a "low key approach". On the contrary, by reporting on the draft report before scientific review was completed, and before the release of a final version, the media presented a distorted view of current research. Sibbison states that the work of Savitz et al4 supports the recommendation that "children and pregnant women should ’avoid electric blankets and pads’ ". In fact, Savitz and colleagues reported a very weak positive association between prenatal exposure to electric blankets and childhood cancers (with a lower confidence interval limit of 0-6); they did not suggest the avoidance of electric blankets. As Cartwrights has stated, "Of the five case-control studies that have attempted to link EMF exposure with childhood leukaemia, the only convincing statistically significant excess remains in the earliest paper. And even this paper suffers from serious drawbacks ... Our present scientific knowledge points at the very best to a minute risk of EMF verging on the point of nonexistence". Other commentaries6-9 point out that, although some investigators have reported evidence of the effects of electromagnetic fields on biological systems, important effects on health are not present. Thus, biological effects are not necessarily biological hazards. The supposed link between electromagnetic fields and hazardous effects is just one of the many topics (at least 5610) in which contradictory and inconsistent results are reported in case-control epidemiological studies. Unfortunately, this supposed link has received undue attention in the popular media. Scientists should attempt to place potential public health risks in their proper perspective and communicate a balanced account of this information to the public and political leaders.
are
Radiation Sciences Division, US Air Force School of Aerospace Medicine, Brooks Air Force Base, Texas 78235, USA
1.
JAMES R. JAUCHEM
Osepchuk JM. Electrophobia. J Microwave Power Electromag Energy 1989; 24: 194. Nurturing electrophobia IEEE Spectrum 1990; 27: 11,14. 3. Saracci R. The IARC monograph program on the evaluation of the carcinogenic risk of chemicals to humans as a contribution of occupational carcinogens. In. Peto R, Schneiderman M, eds. Banbury report 9 quantification of occupational cancer. Cold Habor: Cold Spring Harbor Laboratory, 1981. 165-76 4. Savitz DA, John EM, Kleckner RC. Magnetic field exposure from electric appliances and childhood cancer. Am J Epidemiol 1990; 191: 763-73. 5. Cartwnght RA. Low frequency alternating electromagnetic fields and leukaemia: the saga so far. Br J Cancer 1989; 60: 649-51. 6. Shore RE. Electromagnetic radiations and cancer: cause and prevention. Cancer 1988; 62 (suppl): 1747-54.
2. Adair ER.
7. Knave B, Floderus B. Exposure to low-frequency electromagnetic fields a health hazard? Scand JWork Environ Health 1988; 14 (suppl 1): 46-48. 8. Basset CAL. Fundamental and practical aspects of therapeutic uses of pulsed electromagnetic fields (PEMFs). CRC Crit Rev Biomed Eng 1989; 17: 451—529 9 Cox RAF. Health effects of electromagnetic fields. J R Soc Med 1990; 83: 63-64. 10. Mayes LC, Horwitz RI, Femstein AR. A collection of 56 topics with contradictory results in case-control research. Int J Epidemiol 1988; 17: 680-85.
Shiley heart valves SIR,-Mrs Brahams’ article (Sept 8, p 619) is not a true representation of the facts. Much of the information she reports as findings is based on unsubstantiated allegations made at a US Congressional hearing. Despite the inference within the article the US Congressional Committee did not fmd evidence that Shiley had contravened US laws or regulations. Shiley was not given sufficient opportunity to respond fully to the charges at the hearing. Subsequently, the company submitted a complete rebuttal, which is now in the public record. Most importantly, Shiley has informed doctors of the potential for structural failure, through a series of "Dear Doctor" letters from 1980 to the present. It is indeed true that the company does not wish to create anxiety, especially among patients. Shiley, therefore, wants to ensure that the potential for strut fracture is seen in the proper context. There are various life-threatening risks associated with all heart valves, regardless of manufacturer. Structural failure is one of the least frequent of these risks. The convexo-concave valve has saved tens of thousands of lives and has reduced the most prevalent lifethreatening complication directly related to implantation of heart valves, that of blood clots. This was the primary motivation for the design and development of the convexo-concave valve. Shiley supports the call for legislation for regulation of medical devices in the UK. The UK Department of Health stringently inspects Shiley’s manufacturing plants and the valves are tested by independent laboratories at Sheffield University. The current Shiley heart valve, the monostrut, underwent extensive bench, animal, and clinical evaluation in the early 1980s. Since then, it has been approved for use in many countries, including Sweden, Japan, Australia, and the UK, and has been implanted in some 90 000 patients with no reports of structural failure. The device is currently pending US Food and Drug Administration approval. Shiley European Division. Pfizer Hospital Products Ltd, Staines TW184AN, UK
PHILIP HEDGER
Closure of MRC units SiR,—The impending closure of two further Medical Research Council (MRC) units is clearly of concern to all engaged in the study of the scientific basis of medicine. In the short term, the decision to maintain the project grant system at the expense of the MRC units has the appeal of greater equity and improved competition. However, there is one valuable aspect of the MRC units that has perhaps been overlooked in planning-training responsibilities. A substantial proportion of British scientists (and those from other nations) have begun their research careers in these units. Their particular mixture of intellectual approaches have made them ideal training grounds. It is hard to see how research undertaken in various centres, supported merely by project grants, can offer an individual such comprehensive training. I am concerned that in the longterm the loss of such facilities will severely stunt the next generation of clinical scientists. The consequences of this could be even more devastating than the progressive constriction of research funds; or is there perhaps a macabre logic to it all? Reckitt & Colman Psychopharmacology Unit, School of Medical Sciences, Bristol BS8 1TD, UK
DAVID NUTT
Electromagnetic fields: danger?
is there
a
SIR,-Dr Sibbison (July 14, p 106) comments on supposed hazards
electromagnetic fields. He cites Paul Brodeur’s articles as an example of "the enterprise of investigative reporters" on which "the average citizen must usually rely" for information about potential carcinogens. Three of these articles in New Yorker (and a book dealing with the same information) drew responses from scientists1.22 pointing out how Brodeur oversimplifies the evidence and ignores published work. It is unfortunate that misinformation on the alleged hazards of electromagnetic fields continues to be provided by the lay media when reports of reliable scientific studies in medical journals
from
available. Sibbison suggests that deletions were made from a draft report of the US Environmental Protection Agency (EPA) as a result of political pressure "because utilities executives might complain". In fact, most scientists familiar with this topic realise that (as the director of EPA’s Office of Health and Environmental Assessment has stated) the absence of both a mechanism of interaction and a dose-response relation do not support classification of an electromagnetic field as a "probable" carcinogen. By use of an evaluation process defmed by the International Agency for Research on Cancerinvestigators studying electromagnetic field effects have concluded that the limited and inconsistent data are insufficient to establish a causal association between exposure to electromagnetic fields and cancer. Sibbison also suggests that "front page headlines and segments on national television" were discouraged by a "low key approach". On the contrary, by reporting on the draft report before scientific review was completed, and before the release of a final version, the media presented a distorted view of current research. Sibbison states that the work of Savitz et al4 supports the recommendation that "children and pregnant women should ’avoid electric blankets and pads’ ". In fact, Savitz and colleagues reported a very weak positive association between prenatal exposure to electric blankets and childhood cancers (with a lower confidence interval limit of 0-6); they did not suggest the avoidance of electric blankets. As Cartwrights has stated, "Of the five case-control studies that have attempted to link EMF exposure with childhood leukaemia, the only convincing statistically significant excess remains in the earliest paper. And even this paper suffers from serious drawbacks ... Our present scientific knowledge points at the very best to a minute risk of EMF verging on the point of nonexistence". Other commentaries6-9 point out that, although some investigators have reported evidence of the effects of electromagnetic fields on biological systems, important effects on health are not present. Thus, biological effects are not necessarily biological hazards. The supposed link between electromagnetic fields and hazardous effects is just one of the many topics (at least 5610) in which contradictory and inconsistent results are reported in case-control epidemiological studies. Unfortunately, this supposed link has received undue attention in the popular media. Scientists should attempt to place potential public health risks in their proper perspective and communicate a balanced account of this information to the public and political leaders.
are
Radiation Sciences Division, US Air Force School of Aerospace Medicine, Brooks Air Force Base, Texas 78235, USA
1.
JAMES R. JAUCHEM
Osepchuk JM. Electrophobia. J Microwave Power Electromag Energy 1989; 24: 194. Nurturing electrophobia IEEE Spectrum 1990; 27: 11,14. 3. Saracci R. The IARC monograph program on the evaluation of the carcinogenic risk of chemicals to humans as a contribution of occupational carcinogens. In. Peto R, Schneiderman M, eds. Banbury report 9 quantification of occupational cancer. Cold Habor: Cold Spring Harbor Laboratory, 1981. 165-76 4. Savitz DA, John EM, Kleckner RC. Magnetic field exposure from electric appliances and childhood cancer. Am J Epidemiol 1990; 191: 763-73. 5. Cartwnght RA. Low frequency alternating electromagnetic fields and leukaemia: the saga so far. Br J Cancer 1989; 60: 649-51. 6. Shore RE. Electromagnetic radiations and cancer: cause and prevention. Cancer 1988; 62 (suppl): 1747-54.
2. Adair ER.
7. Knave B, Floderus B. Exposure to low-frequency electromagnetic fields a health hazard? Scand JWork Environ Health 1988; 14 (suppl 1): 46-48. 8. Basset CAL. Fundamental and practical aspects of therapeutic uses of pulsed electromagnetic fields (PEMFs). CRC Crit Rev Biomed Eng 1989; 17: 451—529 9 Cox RAF. Health effects of electromagnetic fields. J R Soc Med 1990; 83: 63-64. 10. Mayes LC, Horwitz RI, Femstein AR. A collection of 56 topics with contradictory results in case-control research. Int J Epidemiol 1988; 17: 680-85.
Shiley heart valves SIR,-Mrs Brahams’ article (Sept 8, p 619) is not a true representation of the facts. Much of the information she reports as findings is based on unsubstantiated allegations made at a US Congressional hearing. Despite the inference within the article the US Congressional Committee did not fmd evidence that Shiley had contravened US laws or regulations. Shiley was not given sufficient opportunity to respond fully to the charges at the hearing. Subsequently, the company submitted a complete rebuttal, which is now in the public record. Most importantly, Shiley has informed doctors of the potential for structural failure, through a series of "Dear Doctor" letters from 1980 to the present. It is indeed true that the company does not wish to create anxiety, especially among patients. Shiley, therefore, wants to ensure that the potential for strut fracture is seen in the proper context. There are various life-threatening risks associated with all heart valves, regardless of manufacturer. Structural failure is one of the least frequent of these risks. The convexo-concave valve has saved tens of thousands of lives and has reduced the most prevalent lifethreatening complication directly related to implantation of heart valves, that of blood clots. This was the primary motivation for the design and development of the convexo-concave valve. Shiley supports the call for legislation for regulation of medical devices in the UK. The UK Department of Health stringently inspects Shiley’s manufacturing plants and the valves are tested by independent laboratories at Sheffield University. The current Shiley heart valve, the monostrut, underwent extensive bench, animal, and clinical evaluation in the early 1980s. Since then, it has been approved for use in many countries, including Sweden, Japan, Australia, and the UK, and has been implanted in some 90 000 patients with no reports of structural failure. The device is currently pending US Food and Drug Administration approval. Shiley European Division. Pfizer Hospital Products Ltd, Staines TW184AN, UK
PHILIP HEDGER
Closure of MRC units SiR,—The impending closure of two further Medical Research Council (MRC) units is clearly of concern to all engaged in the study of the scientific basis of medicine. In the short term, the decision to maintain the project grant system at the expense of the MRC units has the appeal of greater equity and improved competition. However, there is one valuable aspect of the MRC units that has perhaps been overlooked in planning-training responsibilities. A substantial proportion of British scientists (and those from other nations) have begun their research careers in these units. Their particular mixture of intellectual approaches have made them ideal training grounds. It is hard to see how research undertaken in various centres, supported merely by project grants, can offer an individual such comprehensive training. I am concerned that in the longterm the loss of such facilities will severely stunt the next generation of clinical scientists. The consequences of this could be even more devastating than the progressive constriction of research funds; or is there perhaps a macabre logic to it all? Reckitt & Colman Psychopharmacology Unit, School of Medical Sciences, Bristol BS8 1TD, UK
DAVID NUTT
