Re: visual impairment and cancer: a population-based cohort study in Finland.
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Blindness↗
Biomedical subjects
A Ahlbom
Publications and source records attributed to A Ahlbom.
Higher relative, but lower absolute risks of myocardial infarction in women than in men: analysis of some major risk factors in the SHEEP study. The SHEEP Study Group.
OBJECTIVES: Middle-aged men have often been the subjects of multifactorial studies of myocardial infarction (MI) risk factors. One major objective of the SHEEP study was to compare the effects of different MI risk factors in women and men. DESIGN: SHEEP (Stockholm Heart Epidemiology Program) is a population-based case-referent study of causes of MI (first event) in Swedish women and men aged 45-70 years. During the period 1992-94, 2246 cases of MI were identified; 34% of the cases were women and 27% of the cases were fatal. One referent per case was chosen randomly from the Stockholm County population after stratification for the case's sex and age. Logistic regression was used to estimate the relative risks associated with risk factors of primary interest (diabetes, hypercholesterolaemia, hypertriglyceridaemia, hypertension, overweight, physical inactivity, smoking and job strain). RESULTS: The relative risk estimates ranged from 1.5 to 4.4 in women and from 1.3 to 2.9 in men (results for nonfatal cases and their referents). None of the 95% confidence intervals included 1.0. The relative risks were higher in the women than in the men (101-180%). The absolute risks, however, were all lower in the women than in the men. Estimates of Rothman's synergy index for gender ranged from 1.0 (hypertension) to 1.8 (current smoking). CONCLUSIONS: The indications of some effect modification due to sex (stronger risks in men for certain exposures) invoke the question of possible mechanisms.
Aged↗
Geographical differences of cancer incidence in Costa Rica in relation to environmental and occupational pesticide exposure.
BACKGROUND: This study describes geographical differences in cancer incidence in Costa Rica, and investigates if some of these differences may be related to pesticides. METHODS: Data were combined from the cancer registry (1981-1993), the 1984 population census, the 1984 agricultural census, and a national pesticide data set. The 81 counties of Costa Rica were the units for the ecological analyses. Adjacent counties were grouped into 14 regions (3 urban and 11 rural) with relatively similar socioeconomic characteristics. County indices for population density and agricultural variables were constructed and categorized. Differences across regions and categories were assessed by comparing observed numbers of incident cases to expected values derived from national rates. Within the tertile of most rural counties, rate ratios between categories of high and low pesticide use were calculated. RESULTS: In urban regions, excesses were observed for lung, colorectal, breast, uterus, ovary, prostate, testis, kidney, and bladder cancers; and in rural regions for gastric, cervical, penile, and skin cancers. Skin cancers (lip, melanoma, non-melanocytic skin and penile cancer) occurred in excess in coffee growing areas with extensive use of paraquat and lead arsenate. In the most rural subset, heavy pesticide use was associated with an increase of cancer incidence overall and at a considerable number of specific sites, including lung cancer (relative risk [RR] 2.0 for men and 2.6 for women) and all female hormone-related cancers (RR between 1.3 and 1.8). CONCLUSIONS: Regions and populations at high risk for specific cancers were identified. Several hypotheses for associations between pesticides and cancer emerged. The findings call for studies at the individual level.
Confidence Intervals↗
A Bayesian approach to hazard identification. The case of electromagnetic fields and cancer.
This paper discusses certain issues related to uncertainty in hazard identification. Research on the hypothesis that exposure to 50-60-Hz magnetic and electric fields (EMF) increases the risk of cancer has been ongoing for two decades. Epidemiological studies provide a somewhat consistent pattern indicating an increased risk for childhood leukemia and adult chronic lymphatic leukemia and possibly also for other leukemias and brain cancer. However, there is still no good candidate for a mechanism. Epidemiological studies have throughout the two decades been interpreted with great caution, and final evaluations as to carcinogenicity have been deferred. The reason for this carefulness may be the lack of knowledge about a plausible mechanism. The purpose of this paper is to discuss the process of weighing epidemiological data, experimental data, and other background information into a synthesis such that the evaluation can be based on all data combined. A Bayesian approach to this weighing is discussed along with some alternatives. The Bayesian approach provides a structure for the pooling of evidence and points out where subjective judgments come into play.
Adult↗
Re: Use of cellular phones and the risk of brain tumours: a case-control study.
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Adult↗
[Why does the time go faster?].
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Age Factors↗
Is the effect of job strain on myocardial infarction risk due to interaction between high psychological demands and low decision latitude? Results from Stockholm Heart Epidemiology Program (SHEEP).
The objectives are to examine if the excess risk of myocardial infarction from exposure to job strain is due to interaction between high demands and low control and to analyse what role such an interaction has regarding socioeconomic differences in risk of myocardial infarction. The material is a population-based case-referent study having incident first events of myocardial infarction as outcome (SHEEP: Stockholm Heart Epidemiology Program). The analysis is restricted to males 45-64 yr of age with a more detailed analysis confined to those still working at inclusion. In total, 1047 cases and 1450 referents were included in the analysis. Exposure categories of job strain were formed from self reported questionnaire information. The results show that high demands and low decision latitude interact with a synergy index of 7.5 (95% C.I.: 1.8-30.6) providing empirical support for the core mechanism of the job strain model. Manual workers are more susceptible when exposed to job strain and its components and this increased susceptibility explains about 25-50% of the relative excess risk among manual workers. Low decision latitude may also, as a causal link, explain about 30% of the socioeconomic difference in risk of myocardial infarction. The distinction between the interaction and the causal link mechanisms identifies new etiologic questions and intervention alternatives. The specific causes of the increased susceptibility among manual workers to job strain and its components seem to be an interesting and important research question.
Case-Control Studies↗
Occupational exposure to magnetic fields and brain tumours in central Sweden.
Occupations with exposure to magnetic fields were studied in a population-based case-control study of male glioma and meningioma in Central Sweden. The study included 84 cases of glioma, 20 cases of meningioma and 155 controls. Information about job titles was obtained by means of a questionnaire. Three different methods were used to classify exposure 1) 'electrical occupations', 2) assessment of magnetic fields by an electrical engineer, 3) job values based on magnetic field measurements at work sites for occupational groups. When analyses were based on 'electrical occupations' a relative risk (RR) of 1.0 (95% CI: 0.4-2.4) was seen for glioma and 1.8 (95% CI: 0.3-3.6) for meningioma. When analyses were based on measurements a relative risk of 1.9 (95% CI: 0.8-5.0) was seen for glioma and 1.6 (95% CI: 0.3-10.2) for those ever in an exposed job of an average mean value of > 0.4 microT. A larger number of individuals was classified as exposed, when exposure was based on measurements. Information was available regarding several potential confounders, but none of them seemed to be of any importance. Our conclusion is that the results based on magnetic field measurements give some support to the hypothesis that magnetic fields exposure may play a role in the development of brain tumours.
Adult↗
A comprehensive clinical epidemiological theory based on the concept of the source person-time and four distinct study stages.
The medical community is forced to accelerate the move from opinion-based to evidence-based medicine, that is, to aim at basing all caring and clinical practice on empiri. A clear-cut epistemology would facilitate this process. In this article we present a comprehensive clinical epidemiological theory which can be used for validity issues in caring science, quality of life research, controlled clinical trials and compilations of uncontrolled evidence. The theory is based on four distinct stages that can be identified in a study, whereof the first is demarcation of the source person-time. A source person-time ('study base') can be identified for any study in all disciplines, giving an argument for using this concept as the common reference point for validity issues. Apart from identifying the source person-time, recovery of the actually observed person-time, collection of data and calculation of an ('adjusted') effect parameter (e.g., incidence ratio) are additional stages of a study. When the source person-time is demarcated confounding is introduced, when the actually observed person-time is recovered misrepresentation, in the third stage misclassification and in the fourth analytical alteration of the parameter of effect. The concept of the source person-time can, in addition, link examination of validity in caring and clinical sciences to observational studies, thereby allowing the field to benefit from all theoretical achievements for preventing, handling and understanding systematic errors developed in epidemiology. We conclude it is possible to implement a common terminology of validity for all caring and medical sciences. Drawing causal inferences in these disciplines is not mechanical, it can never, for example, be done with statistical inference. Establishing a causal relation always includes an assessment of the magnitude and direction of systematic errors influencing the adjusted effect parameter. From the presented epistemology it follows that differences in validity from a case history to a large randomized, placebo-controlled and double-blinded study are quantitative rather than qualitative. This realization in turn opens up for a more refined discussion of when a decision is evidence-based rather than opinion-based.
Clinical Trials as Topic↗
Socioeconomic differences in risk of myocardial infarction 1971-1994 in Sweden: time trends, relative risks and population attributable risks.
BACKGROUND: The general trend in incidence of myocardial infarction (MI) in the Stockholm area changed from increasing to decreasing around 1980. The objective of this study is to examine time trends in incidence in major socioeconomic strata, relative risk between socioeconomic groups and population risk attributable to socioeconomic differences during this period. METHODS: All cases of MI from 1971 to 1986 were identified from hospital discharge and cause-of-death registers. Person-years for each year of follow-up were calculated from the population register in the Stockholm region 1971-1986. Census registers were used for information on socioeconomic status. Register information was individually linked through the Swedish personal identification number. Supplementary information for 1992-1994 was taken from the case-control study SHEEP (Stockholm Heart Epidemiology Program). RESULTS: The decline in MI risk among male high- and middle-level employees started in 1976 and in male manual workers in 1981. For women incidence increased from 1971 to 1986 among manual workers and decreased among high- and middle-level employees. The increase over time of the relative risk from low socioeconomic position continued into the 1990s. Despite the reduction of the category of manual workers, the population attributable risk from socioeconomic differences also increased over time. The process of social change influencing the size of the socioeconomic groups contributes to the change in time trends of MI morbidity. CONCLUSIONS: The increase over time of relative and population attributable risks of MI from low socioeconomic status add to the public health importance of social inequity.
Adult↗
Electromagnetic fields and childhood leukemia.
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Bias↗
Exposure to motor vehicle exhaust and childhood cancer.
OBJECTIVES: A case-referent study was conducted to test the hypothesis that exposure to motor vehicle exhaust increases the risk of childhood cancer. METHODS: Data from a study of residential magnetic field exposure and childhood cancer were used. From a population of 127000 children living within 300 m of transmission lines in Sweden, 142 cases of childhood cancer were identified, including 39 cases of leukemia and 33 cases of central nervous system tumor. Approximately 4 referents per case were selected at random from the study base. The nitrogen dioxide content of the outdoor air was estimated as an indicator of motor vehicle exhaust. The applied methods give the 99th percentile of the nitrogen dioxide content of the outdoor air for 1-h averages over 1 year. RESULTS: A relative risk estimate of 2.7 [95% confidence interval (95% CI) 0.9-8.5] was found for total cancer at exposure levels of > or = 50 microg/m3, related to those with < or = 39 microg/m3. At > or = 80 microg/m3, the relative risk was estimated at 3.8 (95% CI 1.2-12.1). Elevated, but imprecise risk estimates were found for leukemia and central nervous system tumors. CONCLUSIONS: The results indicate an association between childhood cancer and motor vehicle exhaust, although the number of cases was small. These findings and the results of previous studies suggest that further studies of the association between motor vehicle exhaust and childhood cancer are warranted.
Adolescent↗
Magnetic fields and breast cancer in Swedish adults residing near high-voltage power lines.
We conducted a case-control study to test the hypothesis that residential magnetic field exposures increase the incidence of breast cancer. The study was based on people who had lived within 300 m of 220- or 400-kV power lines in Sweden at any time between 1960 and 1985. We identified 699 cases of breast cancer in women and 9 cases in men. One matched control per female case and eight per male case were selected at random. Estrogen receptor information was available for a subset of female cases. We assessed magnetic field exposure through calculations of the magnetic fields generated by the power lines before diagnosis. For calculated magnetic field levels > or = 0.2 microtesla (microT) closest in times before diagnosis, we estimated the relative risk to be 1.0 [95% confidence interval (CI) = 0.7-1.5] for women and 2.1 (95% CI = 0.3-14.1) for men. Women younger than 50 years of age at diagnosis had a relative risk of 1.8 (95% CI = 0.7-4.3). For women with estrogen receptor-positive breast cancer, the relative risk was estimated at 1.6 (95% CI = 0.6-4.1), using the exposure cutoff point > or = 0.1 microT. Among estrogen receptor-positive women younger than 50 years at diagnosis, the relative risk increased to 7.4 (95% CI = 1.0-178.1).
Adolescent↗
Reduced cancer incidence among the blind.
Melatonin is a hormone primarily produced by the pineal gland at night and is suppressed by exposure to light. Experimental studies have indicated that melatonin may protect against cancer development. In the majority of totally blind people, melatonin is never suppressed by light exposure. The aim of this study was to test the hypothesis that blind people have a decreased cancer incidence, and that this effect is more pronounced in the totally blind than in the severely visually impaired. We identified a cohort of 1,567 totally blind and 13,292 severely visually impaired subjects and obtained information about cancer incidence from the Swedish Cancer Registry. We calculated standardized incidence ratios (SIRs) based on the number of person-years and incidence rates specific for national age, sex, and calendar year. Totally blind people had a lower incidence of all cancers combined [SIR = 0.69; 95% confidence interval (CI) = 0.59-0.82]. The risk reduction was observed in both men and women and was equally pronounced in hormone-dependent tumors as in other types of cancer. In the severely visually impaired, SIR was 0.95 (95% CI = 0.91-1.00). The findings support the hypothesis that blind people have a lower cancer incidence, although other explanations than the higher melatonin exposure must also be considered.
Aged↗
Temporal characteristics of transmission-line loadings in the Swedish childhood cancer study.
A recent study conducted in Sweden reported that 1) leukemia risk in children who lived near 220 or 400 kV electric-power transmission lines was associated with calculated historical magnetic field levels; 2) children living within a distance of 50 m of transmission lines had an elevated risk of leukemia; and 3) there was no association between leukemia and residential magnetic fields measured many years after diagnosis. Subsequently, these investigators found through logistic regression analysis that disease was more strongly associated with calculated historical fields than with distance. Since the calculated historical fields in that study depended predominantly on distance and transmission-line load current, the logistic regression results suggest that historical load current plays an important role in the epidemiological results. Thus, we studied hourly 1974 load-current data for six transmission lines, and we examined 1958-1985 annual load-current data for 112 transmission lines. Most lines exhibited marked diurnal load-current rhythms during 1974, and all six showed systematic weekday-weekend differences. During 1958-1985, average loadings of Swedish 220 and 400 kV lines increased by about 1.3% year. Predictive-value and kappa-statistic analyses indicated that Swedish transmission-line load currents were not stable over long periods, so that contemporaneous load current (or a contemporary magnetic field measurement) was not a good surrogate for historical load current (or historical magnetic fields). The results provide a potential explanation of the failure of the Swedish Study to find an association between leukemia and contemporaneous magnetic field levels measured many years after the etiologic period, and suggest that the inclusion of load-current data could significantly improve the quality of historical field calculations.
Adolescent↗
Dental radiography after age 25 years, amalgam fillings and tumours of the central nervous system.
The aim of the study was to investigate the importance of diagnostic dental radiography and amalgam fillings as risk factors for tumours of the central nervous system (CNS). This population-based case-control study included subjects aged 25-74 years, living in the catchment area of the Neurosurgery Department of Uppsala University Hospital in Sweden. A total of 192 cases of glioma, 99 cases of meningioma and 42 cases of acoustic neurinoma were identified between 1987 and 1990. A control group of 343 subjects was matched on age, gender and parish. Information about dental exposure was obtained by a self-administered questionnaire and from dental records. For those who had a dental radiography at least once a year after age 25 years, a relative risk of 2.1 (95% confidence interval (CI) 1.0-4.3) was seen for meningioma, while for other subgroups of CNS tumours the relative risk was close to unity. No association was observed between the number of amalgam fillings and CNS tumours. In conclusion, there was no clear evidence that dental radiography or amalgam fillings is related to the development of tumours of the CNS.
Adult↗
Cancer in twins: genetic and nongenetic familial risk factors.
BACKGROUND: Familial clustering has been observed for cancers that occur at specific sites. Most findings, which leave little doubt about the involvement of a heritable (i.e., genetic) component in the development of some cancers, are based on data from "cancer-prone" families or interviews with subjects who have cancer. The study of twins should be of value in cancer epidemiology because twins either are genetically identical or share half of their segregating genes. PURPOSE: We linked the Swedish Twin Registry to the Swedish Cancer Registry, thereby identifying cases of cancer diagnosed from 1959 through 1992 in twins born in the period from 1886 through 1958, to assess the importance of both genetic and nongenetic (i.e., environmental) familial factors in determining cancer risk. METHODS: Same-sex twin pairs with both individuals alive and living in Sweden in 1959-1961 or 1970-1972 were identified in the old cohort (born from 1886 through 1925) or the young cohort (born from 1926 through 1958), respectively, of the Swedish Twin Registry; pairs for whom zygosity (i.e., the number of eggs that gave rise to the twins) could be determined were considered further. The association of cancer with combined genetic and nongenetic familial factors was tested by comparing all twin pairs (regardless of zygosity) in which at least one member of the pair had been diagnosed with cancer at one of several specific sites with pairs in which neither twin had that cancer. Heritable effects alone were tested by comparing monozygotic (one egg) and dizygotic (two eggs) twin pairs. Statistical methods used in quantitative genetics and standard methods for epidemiologic research were used in parallel to analyze the data. RESULTS AND CONCLUSIONS: In the 10503 twin pairs from the old cohort, 361.7 cases of malignant cancer were identified; 918 malignant cancers were identified in the 12883 twin pairs from the young cohort. When cancer sites with a total number of at least 200 cases and at least one twin pair concordant (i.e., both twins affected) for the site were evaluated, namely, cancers of the stomach, colon and rectum, lung, female breast, and prostate, as well as total cancer, profound genetic and/or nongenetic familial effects were identified in twins from the old cohort. Similar findings were obtained for twins in the young cohort for cancers of the prostate and female breast, as well as for total cancer. Genetic and nongenetic familial effects were also identified in twins from both cohorts for in situ cancer of the cervix. The increase in risk of colon and rectum, breast, cervical, and especially prostate cancer, but not stomach or lung cancer, tended to be greater if a monozygotic rather than a dizygotic twin were affected. IMPLICATIONS: The identification of familial effects for total cancer in this study is consistent with the idea that individuals may possess a genetic susceptibility to cancer in general.
Adult↗
Heritability for Alzheimer's disease: the study of dementia in Swedish twins.
BACKGROUND: Alzheimer's disease has been thought to have familial and sporadic forms, and several genetic defects have been identified that chiefly explain early-onset familial cases. In this study, our purpose was to detect all cases of dementia in an established twin registry and to estimate total extent of genetic contribution to liability to Alzheimer's disease. METHODS: At the first stage, members of the registry were screened for dementia, using in-person or telephone mental status testing. At the second stage, those who screened positively and their partners were referred for clinical work-ups, including neuropsychological assessment, physician examination, laboratory tests, and neuroimaging. Clinical diagnoses were assigned at a multidisciplinary consensus conference. Probandwise concordance rates were examined by zygosity, and structural modeling was applied to the data to estimate genetic and environmental influences, using both single- and multiple-threshold models. RESULTS: Sixty-five pairs were identified in which one or both was demented. The probandwise concordance rate for Alzheimer's disease among monozygotic pairs was 67%; the corresponding figure for dizygotic pairs was 22%. Heritability of liability to Alzheimer's disease was estimated to be .74; to any dementia, .43. The other variance is attributable to environmental influences. CONCLUSIONS: Findings indicate a substantial genetic effect for these predominantly late-onset Alzheimer's disease cases. At the same time, structural modeling results and large intra-pair differences in age of onset suggest that environmental factors are also important in determining whether and when an individual may develop dementia.
Age of Onset↗