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M Blettner

Publications and source records attributed to M Blettner.

At least 37 records · Page 2Linked to original sources
PubMed2000

Are mobile phones harmful?

There is increasing public interest in health risks of mobile phone use. Although there is a vast body of material on the biological effects of radiofrequency fields, current risk assessment is still limited. The article describes several hypotheses and results of biological effects such as thermal effect, genetic and carcinogenic effects and cancer related investigations. Mobile phones transmit and receive waves of frequencies mainly at 800-1800 MHz. Findings on the thermal effect of acute exposure to radiofrequency fields were consistent, resulting in an increase of cellular, tissue or body temperature by 1 degree C or more. Guidelines for risk limits are based on this thermal effect. Experimental investigation suggests that radiofrequency fields are not tumor initiators and that if they are related to carcinogenicity, this would be by tumor promotion or by increasing the uptake of carcinogens in cells. Implications of these experimental results on public health concerns are yet unclear. Few epidemiological studies are available on the use of mobile phones or on the radiofrequency exposure and the development of cancer. Most of these studies have no or little quantitative exposure data and they are limited by the small number of observations. Large epidemiological studies are necessary in order to investigate the use of mobile phones on the development of cancer. It should be emphasized that even a small elevated risk may have a large implication for public health, as the use of mobile phones and the exposure is rapidly increasing.

Accidents, Traffic↗
PubMed2000

Epidemiologic studies of pilots and aircrew.

During flight, pilots and cabin crew are exposed to increased levels of cosmic radiation which consists primarily of neutrons and gamma rays. Neutron dosimetry is not straightforward, but typical annual effective doses are estimated to range between two and five mSv. Higher dose rates are experienced at the highest altitudes and in the polar regions. Mean doses have been increasing over time as longer flights at higher altitudes have become more frequent. Because there are so few populations exposed to neutrons, studies of airline personnel are of particular interest. However, because the cumulative radiation exposure is so low, statistical power is a major concern. Further, finding an appropriate comparison group is problematic due to selection into these occupations and a number of biases are possible. For example, increased rates of breast cancer among flight attendants have been attributed to reproductive factors such as nulliparity and increased rates of melanoma among pilots have been attributed to excessive sun exposure during leisure time activities. Epidemiologic studies conducted over the last 20 y provide little consistent evidence linking cancer with radiation exposures from air travel.

Aircraft↗
PubMed2000

Measurement error correction using validation data: a review of methods and their applicability in case-control studies.

Measurement error is a serious problem in the analysis of epidemiological data. In the past 20 years, a large number of methods for the correction of measurement error have been developed. While at the beginning mostly methods for cohort studies were considered, recently more attention has been paid to case-control studies. Although a variety of methods have been proposed, they are very rarely used in practice. To stimulate their use and further development, this article provides a comprehensive overview on methods developed for multivariable regression analysis of epidemiologic studies with validation data sets. The methods are systematically classified with respect to the underlying theory. An assessment of prerequisites, assumptions and performance of the available methods is given. Particular attention is paid to applicability to case-control studies and need for further research and development is pointed out.

Bias↗
PubMed1999

Role of medical history in brain tumour development. Results from the international adult brain tumour study.

In an international population-based case-control study carried out in 8 centres in 6 countries, we investigated the role of specific medical conditions in the aetiology of brain tumours in adults. Recruited were 1,178 glioma and 331 meningioma cases and 2,493 age- and gender-matched population controls. Only medical conditions occurring at least 2 years before brain tumour diagnosis were considered. Relative risks (RRs) and 95% confidence intervals (CIs) were estimated using a conditional logistic regression model. Heterogeneity between centres was tested. No association between meningioma and previous medical conditions was observed. For glioma, there was an increased risk associated with epilepsy (RR = 6.55, 95% CI 3.40-12.63), but this was considerably weaker for epilepsy of more than 20 years duration. The risk remained elevated after adjustment for use of anti-epileptic drugs. There was a statistically significant inverse association between glioma and all allergic diseases combined (RR = 0.59, 95% CI 0.49-0.71); this was also observed for specific allergic conditions, namely, asthma and eczema. Subjects who reported a history of infectious diseases (e.g., colds, flu) showed a 30% reduction in risk (RR = 0.72, 95% CI 0.61-0.85). The decreased risks for glioma in subjects reporting a history of allergic conditions or infectious diseases may indicate an influence of immunological factors on the development of glioma. The association between glioma and epilepsy has to be interpreted cautiously and needs further investigation.

Adult↗
PubMed1999

[Is there an increased risk of leukemia, brain tumors or breast cancer after exposure to high-frequency radiation? Review of methods and results of epidemiologic studies].

BACKGROUND: There are only a few epidemiologic studies investigating risk factors in persons occupationally exposed to high-frequency radiation (e.g. radio-, TV-waves, mobile phones or microwaves). The results of the studies are mostly inconsistent. METHODS: All epidemiologic studies which investigated the association between occupational exposure to high-frequency radiation and the risk of leukemia, brain tumors or breast cancer were included in this review. All studies published between 1980 and 1997, such as record-linkage, case-control, and cohort studies, were retrieved from MEDLINE. Incidence and mortality studies are included. Methodologic problems of these investigations are discussed. RESULTS: Most of the recent epidemiologic studies do not present quantitative exposure data or data on the specific frequencies of electro magnetic fields. In general, the relative risks for leukemia, brain tumors or breast cancer are small, not significant and inconsistent. Confounder variables were not included in most of the analyses and no dose-response relationship was reported. CONCLUSION: To increase the power and the validity of the studies a re-analysis based on original data of all previous studies in this field is recommended. Additionally, to investigate the influence of high-frequency radiation on the development of cancer, international epidemiologic studies are necessary. Only they would have sufficient sample size to detect small elevated risks.

Brain Neoplasms↗
PubMed1999

Traditional reviews, meta-analyses and pooled analyses in epidemiology.

BACKGROUND: The use of review articles and meta-analysis has become an important part of epidemiological research, mainly for reconciling previously conducted studies that have inconsistent results. Numerous methodologic issues particularly with respect to biases and the use of meta-analysis are still controversial. METHODS: Four methods summarizing data from epidemiological studies are described. The rationale for meta-analysis and the statistical methods used are outlined. The strengths and limitations of these methods are compared particularly with respect to their ability to investigate heterogeneity between studies and to provide quantitative risk estimation. RESULTS: Meta-analyses from published data are in general insufficient to calculate a pooled estimate since published estimates are based on heterogeneous populations, different study designs and mainly different statistical models. More reliable results can be expected if individual data are available for a pooled analysis, although some heterogeneity still remains. Large prospective planned meta-analysis of multicentre studies would be preferable to investigate small risk factors, however this type of meta-analysis is expensive and time-consuming. CONCLUSION: For a full assessment of risk factors with a high prevalence in the general population, pooling of data will become increasingly important. Future research needs to focus on the deficiencies of review methods, in particular, the errors and biases that can be produced when studies are combined that have used different designs, methods and analytic models.

Breast Neoplasms↗
PubMed1999

Trends in maternal mortality ratio among women of German and non-German nationality in West Germany, 1980-1996.

BACKGROUND: Maternal mortality is a sensitive indicator for inequity in health. We describe recent trends in overall and cause-specific maternal mortality ratio among women of German and non-German nationality residing in West Germany. METHODS: Using birth and death register data for 1980-1996 we related 1067 cases of maternal death (ICD 9: 630-676) to 11.2 million live births. We assessed the effects of nationality and of marital status, a proxy for socioeconomic status, controlling for year of death and age of the mother in a Poisson regression model. RESULTS: Maternal mortality ratio in West Germany decreased from 13 per 100000 live births in 1980-1988 to 6.1 in 1989-1996. The crude relative risk for non-German nationality decreased from 1.9 (95% CI: 1.6-2.3) to 1.3 (1.0-1.7); after adjusting for age, year of death and marital status it was 1.7 (95% CI: 1.4-2.1) and 1.6 (95% CI: 1.2-2.1). Unmarried women incurred an adjusted relative risk of 1.8 (95% CI: 1.5-2.3). Non-German women experienced an excess mortality from abortions which largely disappeared in 1989-1996; concurrently, being unmarried no longer conveyed an additional risk to them. The risk status of German mothers developed unfavourably: increasing proportions are unmarried, which continues to be a marker of elevated relative risk in this group. CONCLUSIONS: Our findings suggest continuously improving accessibility and quality of obstetric services, in particular for women of non-German nationality. Still, inequity in maternal risk continues to exist. Maternal risk, however, is not determined by the simple distinction 'German' versus 'non-German'; its association with socioeconomic status extends beyond nationality.

Abortion, Induced↗
PubMed1998

[Meta-analysis of epidemiologic studies].

BACKGROUND: A metaanalysis is often performed if risk assessment with available epidemiological data is not sensible. The results of these analyses serve mainly to quantify the risk of weak associations. MATERIAL AND METHODS: In this paper we describe methodologic issues of this approach with emphasis on the difference between metaanalysis from published data and from individual patient records. As an example we discuss studies on oral contraceptives and breast cancer. Limits of metaanalysis from published data are given. CONCLUSION: Although metaanalysis with individual data may be cost- and time-consuming their results are more reliable.

Breast Neoplasms↗
PubMed1998

Major locus influencing plasma APO-A1 levels also controls plasma HDL3-C concentrations.

Elevated plasma levels of apolipoprotein A1 (APO-A1) and high-density lipoprotein cholesterol (HDL-C) are important protective factors for atherosclerosis and coronary heart disease. Using the data on plasma concentrations of APO-A1, and HDL-C particles HDL2-C and HDL3-C in 970 Israeli individuals belonging to 228 pedigrees, we tested the hypothesis that a major locus influencing interindividual variation in APO-A1 levels also controls interindividual variation in HDL3-C and HDL2-C levels. Univariate and bivariate complex segregation analyses, as implemented in two statistical packages (MAN-3 and PAP-4.0) were applied to test the hypothesis. The results of the analysis clearly indicated the possibility of major gene involvement in the determination of plasma concentration variation of each of the 3 study variables. The results provide strong evidence in support of our hypothesis that HDL3-C genetic variation fully depends on the APO-A1 major locus. In particular, environmental and sporadic models were strongly rejected (P < 0.001) in bivariate analysis. The hypothesis of no pleiotropic effect of the putative APO-A1 locus on HDL3-C transmission was also unequivocally rejected (P < 0.001), while the bivariate Mendelian model was accepted (P > 0.05). The results of bivariate analysis of APO-A1 effect on HDL2-C were not clear. They indicated the possibility of the existence of slight genetic covariation between the two variables, and as yet we were unable to decipher the mode of covariation with the applied models.

Apolipoprotein A-I↗
PubMed1998

Identifying influential families using regression diagnostics for generalized estimating equations.

The Generalized Estimating Equations (GEE) is an approach to analyze correlated data. It is applied here to data from an epidemiological study of oesophageal cancer in a high incidence area in China to investigate familial aggregation. Regression diagnostics for mean structures and association structures are used to identify families that influence estimates of these structures. It is shown that most of the families influencing the mean structure have a low age of disease onset in common. Most families identified by regression diagnostics for the association structure influence the parent correlation. It is concluded that regression diagnostic techniques can be used to identify clusters influencing mean and association structures of the models.

China↗
PubMed1998

Adult leukaemia: what is the role of currently known risk factors?

Leukaemias are a heterogeneous group of tumours including acute and chronic forms. Considerable efforts have been made to identify risk factors for these diseases, but only a minority of leukaemia cases can currently be attributed to identified or hypothesized factors. This review highlights recent epidemiological literature concerning adult leukaemia, discussing in detail the hereditary, environmental and medical risks. Chromosomal syndromes and genetically based diseases carry a high risk of leukaemia, but rarely occur in the population. Environmental and occupational exposures to chemicals including pesticides have been widely studied, although the results are not consistent, with the exception of benzene. Smoking seems to be a weak causal risk factor. The risk of ionizing radiation has further been quantified in recent studies, although the effects of low doses have not yet been clarified. The results for non-ionizing radiation continue to be inconsistent, but a large effect of electromagnetic fields on the risk of leukaemia appears to be unlikely. Medically applied radio- and chemotherapy are clearly associated with subsequent leukaemia development, and there are links between leukaemia and viral infections. Future research should emphasize the shortcomings in exposure assessment that pervade many studies, and interactions between different risk factors need to be taken into consideration.

Adult↗
PubMed1998

Occupational cancer risk in pilots and flight attendants: current epidemiological knowledge.

Occupational studies of aircrew in civil or military aviation did not receive much attention until the beginning of this decade. Since 1990, a number of epidemiological studies has been published on the cancer risk among flight personnel. Their results are equivocal: elevated cancer risks have been observed in some studies, but not in others. The exposure situation for pilots and flight attendants is unique with respect to several factors and particularly in that cosmic rays contribute substantially to their cumulative radiation dose. The average annual doses received are relatively low, however, and commonly range between 3 and 6 mSv. Results of epidemiological studies are presented as well as information on planned studies.

Aviation↗