CEGB cohort

Occup Environ Med 1997 Jan;54(1):7-13
Occupational exposure to magnetic fields in relation to mortality from brain cancer among electricity generation and transmission workers.

Harrington JM, McBride DI, Sorahan T, Paddle GM, van Tongeren M.

Institute of Occupational Health, University of Birmingham, Edgbaston.

OBJECTIVE: To investigate whether the risks of mortality from brain cancer are related to occupational exposure to magnetic fields. METHODS: A total of 112 cases of primary brain cancer (1972-91) were identified from a cohort of 84,018 male and female employees of the (then) Central Electricity Generating Board and its privatised successor companies. Individual cumulative occupational exposures to magnetic fields were estimated by linking available computerised job history data with magnetic field measurements collected over 675 person-workshifts. Estimated exposure histories of the case workers were compared with those of 654 control workers drawn from the cohort (nested case-control study), by means of conditional logistic regression. RESULTS: For exposure assessments based on arithmetic means, the risk of mortality from brain cancer for subjects with an estimated cumulative exposure to magnetic fields of 5.4-13.4 microT.y v subjects with lower exposures (0.0-5.3 microT.y) was 1.04 (95% confidence interval (95% CI) 0.60 to 1.80). The corresponding relative risk in subjects with higher exposures (> or = 13.5 microT.y) was 0.95 (95% CI 0.54 to 1.69). There was no indication of a positive trend for cumulative exposure and risk of mortality from brain cancer either when the analysis used exposure assessments based on geometric means or when the analysis was restricted to exposures received within five years of the case diagnosis (or corresponding period for controls). CONCLUSIONS: Although the exposure categorisation was based solely on recent observations, the study findings do not support the hypothesis that the risk of brain cancer is associated with occupational exposure to magnetic fields.

Occup Environ Med 2001 May;58(5):307-14
Leukaemia mortality in relation to magnetic field exposure: findings from a study of United Kingdom electricity generation and transmission workers, 1973-97.

Harrington JM, Nichols L, Sorahan T, van Tongeren M.

Institute of Occupational Health, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK.

OBJECTIVE: To investigate whether risks of leukaemia are related to occupational exposure to magnetic fields. METHODS: The mortality experienced by a cohort of 83 997 employees of the former Central Electricity Generating Board of England and Wales was investigated for the period 1973-97. All employees were employed for at least 6 months with some employment in the period 1973-82. Computerised work histories were available for 79 972 study subjects for the period 1971-93. Detailed calculations were performed by others to enable a novel assessment to be made of exposures to magnetic fields. Two analytical approaches were used, indirect standardisation (n=83 997) and Poisson regression (n=79 972). RESULTS: Based on serial mortalities for England and Wales, the standardised mortality ratio of 84 for all leukaemias (observed 111, expected 132.3) was similar to that of 83 for all causes (observed 14 845, expected 17 918). No significant positive trends were found for the risks of various types of leukaemia (chronic lymphatic leukaemia, acute myeloid leukaemia, chronic myeloid leukaemia, all leukaemia) either with lifetime cumulative exposure to magnetic fields or with such exposures received in the most recent 5 years. CONCLUSIONS: There are no discernible excess risks of leukaemia as a consequence of occupational exposure to magnetic fields in United Kingdom electricity generation and transmission workers.

Occup Environ Med 2001 Oct;58(10):626-30
Occupational exposure to magnetic fields relative to mortality from brain tumours: updated and revised findings from a study of United Kingdom electricity generation and transmission workers, 1973-97.

Sorahan T, Nichols L, van Tongeren M, Harrington JM.

Institute of Occupational Health, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK. T.M.Sorahan@bham.ac.uk

OBJECTIVE: To investigate whether risk of brain tumour is related to occupational exposure to magnetic fields. METHODS: The mortality experienced by a cohort of 83 997 employees of the former Central Electricity Generating Board of England and Wales was investigated for the period 1973-97. All workers were employed for at least 6 months with some employment in the period 1973-82. Computerised work histories were available for 79 972 study subjects for the period 1971-93. Detailed calculations had been performed by others to enable a novel assessment to be made of exposures to magnetic fields. Two analytical approaches were used, indirect standardisation (n=83 997) and Poisson regression (n=79 972). RESULTS: Based on serial mortalities for England and Wales, deaths from brain cancer were close to expectation (observed 158, expected 146.4). No significant positive trends were shown for risks of brain tumours either with lifetime cumulative exposure to magnetic fields or with such exposures received in the most recent 5 years. CONCLUSIONS: There are no discernible excess risks of brain tumours as a consequence of occupational exposure to magnetic fields in United Kingdom electricity generation and transmission workers.

Sorahan T, Nichols L.

Institute of Occupational Health, University of Birmingham, Edgbaston, Birmingham, United Kingdom.

BACKGROUND: Experimental and epidemiological studies have indicated that magnetic field exposure might influence heart rate variability and consequent risks of arrhythmia related deaths. METHODS: The mortality experience of a cohort of 83,997 employees of the former Central Electricity Generating Board (CEGB) of England and Wales was investigated for the period 1973-1997. Cohort members were employed for at least 6 months from 1973 to 1982. Computerized work histories were available for 79,972 study subjects for the period 1971-1993. Detailed calculations had been performed by others to enable a novel assessment to be made of exposures to magnetic fields. Two analytical approaches were used, indirect standardization (n = 83,997) and Poisson regression (n = 79,972). RESULTS: Based on serial mortality rates for England and Wales, deaths from four categories of cardiovascular disease were below expectation: arrhythmia-related disease (ICD-9 426-7), observed (obs) 32, expected (exp) 43.5, standardized mortality ratio (SMR) 74; acute myocardial infarction (ICD-9 410), obs 3,320, exp 3878.3, SMR 86; atherosclerosis (ICD-9 440), obs 25, exp 39.2, SMR 64; chronic/sub-acute coronary disease (ICD-9 411-414), obs 1,552, exp 2021.7, SMR 77). No statistically significant trends were shown for risks of any of these four disease groupings to increase either with lifetime cumulative exposure to magnetic fields or with such exposures received in the most recent 5 years. CONCLUSIONS: There are no discernible excess risks of mortality from cardiovascular diseases as a consequence of occupational exposure to magnetic fields in UK electricity generation and transmission workers.

Clinicians didn't reliably distinguish between different causes of cardiac death using case histories

Mant J, Wilson S, Parry J, Bridge P, Wilson R, Murdoch W, Quirke T, Davies M, Gammage M, Harrison R, Warfield A.

BACKGROUND AND OBJECTIVES: Routine statistics and epidemiologic studies often distinguish between types of cardiac death. Our aim was to assess agreement between doctors on cause of death given identical clinical information, and to assess agreement between a physician panel and the original cause of death as coded on national statistics. METHODS: Clinical information and autopsy reports on 400 cardiac deaths were randomly selected from a defined population in the West Midlands, UK. A panel of eight clinicians was assembled, and batches of 24-25 cases were sent to pairs of these clinicians who, blinded to the certified cause of death, independently of each other assigned underlying cause of death. Physician panel decision was achieved by consensus. Levels of agreement were assessed using the kappa statistic. RESULTS: Reviewers agreed on cause of death in 54% of cases (kappa = 0.34). Consensus decision of reviewers agreed with death certificate diagnosis in 61.5% (kappa = 0.39). Agreement was higher if an autopsy had been performed (kappa = 0.49). CONCLUSION: The process of identifying underlying cause of death is of limited reliability, and therefore, limited accuracy. This has implications for design of epidemiologic studies and clinical trials of cardiovascular disease.

Renew DC, Cook RF, Ball MC.

National Grid Transco plc. 1-3 Strand, London WC2N 5EH, UK.

ABSTRACT: A new method for assessing both current and historical occupational exposures to magnetic fields has been developed and used in health studies involving a cohort of electricity generation and transmission workers in England and Wales. The exposure values are derived by calculation from engineering and operational data about the power stations rather than from measurements. They are provided for each of 11 job categories for each year of operation of each power station represented in the cohort. The engineering data are used to determine the average magnetic fields in specified areas of work within the power station and then applied to information about the time spent in these areas by each of the job categories. The operational data are used to adjust the exposures for each year according to the power station output for the year. Earlier methods used measurements or the advice of panels of experts to provide exposure scores for a number of job categories across all power stations and years. Such methods were not able to distinguish exposures from different power facilities or during the different years of their operation. Measurement surveys at 10 power stations of the magnetic fields in the work areas gave confidence that the calculations were realistic. Exposure measurements on 215 workers at three power stations were compared in job groups with the exposures predicted by the method. The Pearson correlation coefficient was 0.86 and the slope and intercept of the line of best fit were 0.87 and 0.07 microT respectively. The method gives a good prediction of measured exposure and is being used for studies of occupational exposure to magnetic fields and leukaemia, and of cardiovascular disease, and a reanalysis of brain cancer.

Nichols L, Sorahan T.

OBJECTIVE: To examine mortality from cancer and non-malignant causes among a large cohort of UK electricity generation and transmission workers. METHODS: The mortality experienced by a cohort of 83,923 employees of the former Central Electricity Generating Board of England and Wales was investigated for the period 1973-2002. All employees had worked for at least 6 months with some employment between 1973 and 1982. Standardized mortality ratios (SMRs) were used to assess mortality in the total cohort and in three sub-cohorts: power station workers, substation and transmission workers and workers at non-operational locations. These classifications were based on the place of work of the first known job. RESULTS: Overall mortality was significantly below that expected, based on national rates [males: observed (Obs) 18,773, expected (Exp) 22,497.9, SMR 83; females: Obs 1122, Exp 1424.9, SMR 79]. Statistically significant deficits of deaths were also found for most of the major disease groupings. However, significant excesses of deaths were found in male power station workers for cancer of the pleura (Obs 129, Exp 30.3, SMR 426) and in male workers from non-operational locations for cancer of the brain (Obs 55, Exp 36.0, SMR 153). There was also a non-significant excess of deaths from cancer of the breast in male power station workers (Obs 10, Exp 5.3, SMR 190). CONCLUSIONS: Mortality was exceptionally low for most causes of death but late health effects from earlier asbestos exposure were still in evidence.

Sorahan T, Kheifets L.

University of Birmingham, United Kingdom.

BACKGROUND: There are a number of reports linking magnetic field exposure to increased risks of Alzheimer's disease and motor neurone disease. METHODS: The mortality experienced by a cohort of 83,997 employees of the former Central Electricity Generating Board of England and Wales was investigated for the period 1973-2004. All employees were employed for at least six months with some employment in the period 1973-82. Computerised work histories were available for 79,972 study subjects for the period 1971-93. Information on job and facility (location) were used to estimate exposures to magnetic fields. Two analytical approaches were used to evaluate risks, indirect standardisation (n = 83,997) and Poisson regression (n = 79,972). RESULTS: Based on serial mortality rates for England and Wales, deaths from Alzheimer's disease and motor neurone disease were unexceptional. There was an excess of deaths from Parkinson's disease of borderline significance. No statistically significant trends were shown for risks of any of these diseases to increase with lifetime cumulative exposure to magnetic fields (RR per 10mT.y with 95% confidence interval: Alzheimer's disease 1.10 (0.90 to 1.33); motor neurone disease 1.06 (0.86 to 1.32); Parkinson's disease 0.88 (0.74 to 1.05)) CONCLUSIONS: There is no evidence that UK electricity generation and transmission workers have suffered elevated risks from neurodegenerative diseases as a consequence of exposure to magnetic fields.