CEGB Cohort Study
Cohort of UK electricity industry workers
The UK electricity industry supports research into the health of its own workers. A database of everyone who worked for the then Central Electricity Generating Board (CEGB) in the late 1970s, including over 80,000 people, is maintained for occupational research. When members of this database eventually die, the cause of death is recorded. New techniques have been developed for assessing people’s exposure to magnetic fields over their working life. It is then possible to see whether the cause of death is linked to exposure to magnetic fields.
A major expansion of the use of this cohort was the decision in 2009 to start collecting data on cancer incidence, not just on causes of death.
Results so far
Analyses so far have shown no association between leukaemia, brain cancers, heart disease or neurodegenerative disorders and magnetic fields. The abstracts of all these papers are available here.
The first publication in 1997 looked at magnetic fields and brain cancer (https://pubmed.ncbi.nlm.nih.gov/11555682/), and concluded:
“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.”
The second publication in 2001 used a new method for exposure assessment, developed by scientists at National Grid. This exposure assessment is now more sophisticated than used in most previous studies of this type (https://pubmed.ncbi.nlm.nih.gov/11303079/). The paper looked at magnetic fields and leukaemia, and concluded:
“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.”
The third publication, also in 2001, used the improved exposure assessment to reanalyse the data on brain cancers (https://pubmed.ncbi.nlm.nih.gov/11555682/), and concluded:
“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.”
The fourth publication, in 2004, looked at heart disease (https://pubmed.ncbi.nlm.nih.gov/14691973/), and concluded:
“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.”
A follow-up publication concluded that death certificates have only very limited accuracy at distinguishing different types of heart disease, and therefore some of the previous epidemiological studies of EMFs and heart disease are methodologically suspect.
The fifth publication, in 2005, compared mortality in the group as a whole with the general population (https://academic.oup.com/occmed/article/55/7/541/1422100), and concluded:
“Mortality was exceptionally low for most causes of death but late health effects from earlier asbestos exposure were still in evidence.”
The sixth publication, in 2007, looked at neurodegenerative disorders (Alzheimer's disease, motor neurone disease and Parkinson's disease) (https://pubmed.ncbi.nlm.nih.gov/17626136/) and concluded:
“There is no convincing evidence that UK electricity generation and transmission workers have suffered increased risks from neurodegenerative diseases as a consequence of exposure to magnetic fields.”
The study design has now been expanded from just mortality data to include cancer incidence data. The first publication on cancer incidence in 2012 (https://pubmed.ncbi.nlm.nih.gov/22949586/) found an excess of mesothelioma (attributed to asbestos in power stations), no accompanying excess of lung cancer (attributed to the smoking rates being lower than the general population), and "unexceptional" results for brain cancers and leukaemia:
"Overall cancer morbidity was slightly below expectation in males and females. Significant excesses were found in male workers for mesothelioma (Observed [Obs] 504, SRR 331), skin cancer (non-melanoma) (Obs 3187, SRR 107) and prostate cancer (Obs 2684, SRR 107) and in female workers for cancer of the small intestine (Obs 10, SRR 306) and nasal cancer (Obs 9, SRR 474). Brain cancers were close to expectation in males and below expectation in females. Leukaemia incidence (all types) was slightly below expectation in males and females."
This latest study, published in 2019 (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6704976/) has expanded the cancer registry data to include those up to the end of 2015, an additional 7 years of data. The key findings are:
"Overall cancer morbidity was slightly below expectation in males. Significant excesses were found in male workers for mesothelioma (observed [Obs] 763, SRR 326), skin cancer (non-melanoma) (Obs 5616, SRR 106), and prostate cancer (Obs 4298, SRR 106), and in female workers for cancer of the small intestine (Obs 13, SRR 220), nasal cancer (Obs 11, SRR 407), and breast cancer (Obs 758, SRR 110). More detailed analyses showed important contrasts, particularly for mesothelioma, lung cancer, skin cancer, prostate cancer and breast cancer."
Similar to the 2011 results, an excess of mesothelioma was attributed to asbestos in power stations, and those who work outside and get lots of sun exposure have an increased risk of skin cancer. There was no demonstrable relationship between prostate cancer in men and their occupation, nor between occupation, nasal cancer, cancer of the small intestine or breast cancer in women.
Using the new data on cancer incidence as well as mortality (https://pubmed.ncbi.nlm.nih.gov/24562302/), two new studies looked again at leukaemia and brain tumours, concluding:
"This study found no evidence to support the hypothesis that exposure to magnetic fields is a risk factor for gliomas, and the findings are consistent with the hypotheses that both distant and recent magnetic field exposures are not causally related to gliomas. The limited positive findings for meningioma may be chance findings; national comparisons argue against a causal interpretation."
"This study found no convincing evidence to support the hypothesis that exposure to magnetic fields is a risk factor for leukaemia, and the findings are consistent with the hypotheses that both distant and recent magnetic field exposures are not causally related to the generality of leukaemia. The limited positive findings for ALL may well be chance findings."
A 2014 paper revisited neurodegenerative disorders (https://pubmed.ncbi.nlm.nih.gov/25104278/), adding a further 6 years of data to the previous analysis, and concluded:
"RESULTS: No statistically significant trends were shown for risks of any of these diseases to increase with estimates of lifetime, recent or distant exposure to magnetic fields.
CONCLUSIONS: There is no convincing evidence that UK electricity generation and transmission workers have suffered elevated risks from neurodegenerative diseases as a consequence of exposure to magnetic fields."
Future directions
Although not directly part of the research based on this cohort, the UK electricity industry sponsored a workshop in Edinburgh in 2006 for the people involved in these studies and in similar work in other countries to discuss possible future directions for such research. The conclusions were published in a peer-reviewed paper (https://pubmed.ncbi.nlm.nih.gov/18805878/). The abstract concluded:
“The occupational epidemiological literature on extremely low frequency electric and magnetic fields (EMF) and health encompasses a large number of studies of varying design and quality that have addressed many health outcomes, including various cancers, cardiovascular disease, depression and suicide, and neurodegenerative diseases, such as Alzheimer disease and amyotrophic lateral sclerosis (ALS). At a 2006 workshop we reviewed studies of occupational EMF exposure with an emphasis on methodological weaknesses, and proposed analytical ways to address some of these. We also developed research priorities that we hope will address remaining uncertainties. Broadly speaking, extensive epidemiological research conducted during the past 20 years on occupational EMF exposure does not indicate strong or consistent associations with cancer or any other health outcomes. Inconsistent results for many of the outcomes may be attributable to numerous shortcomings in the studies, most notably in exposure assessment. There is, however, no obvious correlation between exposure assessment quality and observed associations. Nevertheless, for future research, the highest priorities emerge in both the areas of exposure assessment and investigation of ALS. To better assess exposure, we call for the development of a more complete job-exposure matrix that combines job title, work environment and task, and an index of exposure to electric fields, magnetic fields, spark discharge, contact current, and other chemical and physical agents. For ALS, we propose an international collaborative study capable of illuminating a reported association with electrical occupations by disentangling the potential roles of electric shocks, magnetic fields and bias. Such a study will potentially lead to evidence-based measures to protect public health”
Work on exposure assessment methods
The work that was done (by National Grid) on developing improved methods of assessing exposure for these studies showed that "job" is often only a poor predictor of exposure: you need to include "site" or "task" as well to be able to predict exposure. This point was made in a Letter to the Editor in 2017: “Does ‘job’ predict exposure to magnetic fields?” (https://oem.bmj.com/content/74/12/925.1).