Search PubMed⌕ Search

Biomedical subjects

Maria Blettner

Publications and source records attributed to Maria Blettner.

27 records · Page 2Linked to original sources
PubMed2003

Biological effects on human health due to radiofrequency/microwave exposure: a synopsis of cohort studies.

We evaluated the methods and results of nine cohort studies dealing with the biological effects on human health from exposure to radiofrequencies/microwaves, published between 1980 and 2002. The size of the cohorts varied between 304 (3,362 person years) and nearly 200,000 persons (2.7 million person years). As exposures were defined: dielectric heaters in a plastic manufacturing plant, working with radio devices (professional and amateur), production of wireless communication technologies, radar devices of the Canadian police, radar units used by the military as well as artificially produced electromagnetic pulses similar to those after a nuclear explosion. In all studies (except one that used a qualitative job-exposure-matrix) either the duration of occupational work as an approximation to actual exposure was determined or a simple yes/no differentiation was used based on a definition of high-exposed and/or low-exposed (occupational) groups. Either total mortality, cancer mortality, cancer incidence or other outcomes were estimated. In most of the studies, an increased risk for various types of cancer was found in exposed study participants, although in different organs. The overall results were, however, inconsistent. The most important limitations of the studies were the lack of measurements referring to past and current exposures and, thus, the unknown details on actual exposure, the use of possibly biased data as well as the lack of adjustment for potential confounders and the use of indirect standardization techniques. Due to these limitations and the inconsistencies of the results it has to be concluded that the studies give no evidence of high frequency emissions causing cancer.

Cohort Studies↗
PubMed2003

Mortality from cancer and other causes among airline cabin attendants in Europe: a collaborative cohort study in eight countries.

There is concern about the health effects of exposure to cosmic radiation during air travel. To study the potential health effects of this and occupational exposures, the authors investigated mortality patterns among more than 44,000 airline cabin crew members in Europe. A cohort study was performed in eight European countries, yielding approximately 655,000 person-years of follow-up. Observed numbers of deaths were compared with expected numbers based on national mortality rates. Among female cabin crew, overall mortality (standardized mortality ratio (SMR) = 0.80, 95% confidence interval (CI): 0.73, 0.88) and all-cancer mortality (SMR = 0.78, 95% CI: 0.66, 0.95) were slightly reduced, while breast cancer mortality was slightly but nonsignificantly increased (SMR = 1.11, 95% CI: 0.82, 1.48). In contrast, overall mortality (SMR = 1.09, 95% CI: 1.00, 1.18) and mortality from skin cancer (for malignant melanoma, SMR = 1.93, 95% CI: 0.70, 4.44) among male cabin crew were somewhat increased. The authors noted excess mortality from aircraft accidents and from acquired immunodeficiency syndrome in males. Among airline cabin crew in Europe, there was no increase in mortality that could be attributed to cosmic radiation or other occupational exposures to any substantial extent. The risk of skin cancer among male crew members requires further attention.

Adult↗
PubMed2003

Helicobacter pylori and carcinogenesis of gastric B-cell lymphomas.

Primary non-Hodgkin's lymphomas of the stomach are associated with Helicobacter pylori infection. We analyzed gastric lymphoma onset data with respect to prior H. pylori infections based on the multistage theory of carcinogenesis. This theory provides a link between epidemiological data and biological processes. The study involved 133 patients, aged 29-75 years, diagnosed with marginal zone B-cell lymphoma (MZBL) and diffuse large cell B-cell lymphoma (DLBL). A 2-parametric Weibull model was applied to MZBL and DLBL onset data. Median age of diagnosis of MZBL (DLBL) was 59 years (55 years) in males and 65.5 years (64 years) in females. Infection with H. pylori was found in 81.3% (59.5%) of the patients diagnosed with MZBL (DLBL). Lymphoma latency data were fitted to Weibull distributions with a shape parameter of 5.7 for MZBL cases and 4.2 for DLBL. The shape parameter that indicates the number of steps in carcinogenesis was approximately independent of the status of infection with H. pylori in DLBL in contrast to MZBL. It was shown that gastric lymphoma onset data can be described by Weibull distribution functions. The findings support the hypothesis that MZBL and DLBL have different lines of development. There is indication of stronger antigen dependency in the carcinogenesis of MZBL in comparison to DLBL.

Adult↗
PubMed2002

Mortality from cancer and other causes among airline cabin attendants in Germany, 1960-1997.

Airline cabin attendants are exposed to several potential occupational hazards, including cosmic radiation. Little is known about the mortality pattern and cancer risk of these persons. The authors conducted a historical cohort study among cabin attendants who had been employed by two German airlines in 1953 or later. Mortality follow-up was completed through December 31, 1997. The authors computed standardized mortality ratios (SMRs) for specific causes of death using German population rates. The effect of duration of employment was evaluated with Poisson regression. The cohort included 16,014 women and 4,537 men (approximately 250,000 person-years of follow-up). Among women, the total number of deaths (n = 141) was lower than expected (SMR = 0.79, 95% confidence interval (CI): 0.67, 0.94). The SMR for all cancers (n = 44) was 0.79 (95% CI: 0.54, 1.17), and the SMR for breast cancer (n = 19) was 1.28 (95% CI: 0.72, 2.20). The SMR did not increase with duration of employment. Among men, 170 deaths were observed (SMR = 1.10, 95% CI: 0.94, 1.28). The SMR for all cancers (n = 21) was 0.71 (95% CI: 0.41, 1.18). The authors found a high number of deaths from acquired immunodeficiency syndrome (SMR = 40; 95% CI: 28.9, 55.8) and from aircraft accidents among the men. In this cohort, ionizing radiation probably contributed less to the small excess in breast cancer mortality than reproductive risk factors. Occupational causes seem not to contribute strongly to the mortality of airline cabin attendants.

Accidents, Aviation↗
PubMed2002

Calculating the "number needed to be exposed" with adjustment for confounding variables in epidemiological studies.

The number needed to treat (NNT) is a popular summary statistic to describe the absolute effect of a new treatment compared with a standard treatment or control concerning the risk of an adverse event. The NNT concept can be applied whenever the risk of an adverse event is compared between two groups; for the comparison of exposed with unexposed subjects in epidemiological studies, we propose the term "number needed to be exposed" (NNE). Whereas in randomized clinical trials NNT can be calculated on the basis of a simple 2 x 2 table, in epidemiological studies methods to adjust for confounders are required in most applications. We derive a method based upon multiple logistic regression analysis to perform point and interval estimation of NNE with adjustment for confounding variables. The adjusted NNE can be calculated from the adjusted odds ratio (OR) and the unexposed event rate (UER) estimated by means of an appropriate multiple logistic regression model. As UER is dependent on the confounders, the adjusted NNEs also vary with the values of the confounding variables. Two methods are proposed to take the dependence of NNE on the values of the confounders into account. The adjusted number needed to be exposed can be a useful complement to the commonly presented results in epidemiological studies, such as ORs and attributable risks.

Clinical Trials as Topic↗
PubMed2002

Sun exposure and number of nevi in 5- to 6-year-old European children.

The occurrence and number of melanocytic nevi are among the most important known risk factors for the development of malignant melanoma. Studying the causes of nevi should lead to successful strategies in the prevention of melanoma. Among 11,478 white German children of preschool age the association between benign melanocytic nevi and a number of risk factors for skin cancer was examined. We found that subjects with a reported history of increased sun exposure, for example, painful sunburns, and an increased number of holidays in foreign countries with a sunny climate had significantly higher nevus counts than individuals without these characteristics. Our results provide further evidence that nevus counts may not only be part of a genetic predisposition but also a result of increased exposure to ultraviolet radiation. Together with the fact that a high nevus count is the most relevant risk factor for malignant melanoma, the results strongly indicate a connection between UV-radiation and the development of melanocytic skin cancer. In conclusion, strategies to reduce the incidence of melanoma should begin with young children.

Child↗
PubMed2002

The performance of methods for correcting measurement error in case-control studies.

BACKGROUND: It is generally agreed that adjustment for measurement error (when feasible) can substantially increase the validity of epidemiologic analyses. Although a broad variety of methods for measurement error correction has been developed, application in practice is rare. One reason may be that little is known about the robustness of these methods against violations of their restrictive assumptions. METHODS: We carried out a simulation study to assess the performance of two error correction methods (a regression calibration method and a semiparametric approach) as compared with standard analyses without measurement error correction in case-control studies with internal validation data. Performance was assessed over a wide range of model parameters including varying degrees of violations of assumptions. RESULTS: In nearly all the settings assessed, the semiparametric estimate performed better than all alternatives under investigation. The regression calibration method is sensitive to violations of the assumptions of nondifferential error and small error variance. CONCLUSIONS: The semiparametric method is a very robust method to correct for measurement error in case-control studies, but lack of functional software hinders widespread use. If the assumptions for the regression calibration method are fulfilled, application of this method, originally developed for cohort studies, in case-control studies may be a useful alternative that is easy to implement.

Bias↗
PubMed2002

Cohort mortality study of German cockpit crew, 1960-1997.

BACKGROUND: Cockpit crew in civil aviation are exposed to several potential health hazards, among them cosmic ionizing radiation. To assess the influence of occupational and other factors on mortality we conducted a cohort study among cockpit crew. METHODS: All pilots and other cockpit personnel of two German airlines were traced through registries and other sources for the period 1960-1997. Standardized mortality ratios, with German population rates as the reference, were calculated. We estimated the individual radiation dose based on individual job histories and assessed dose-response trends in stratified and regression analyses. RESULTS: We compiled a cohort of 6061 male cockpit personnel, yielding 105,037 person-years of observation. The maximum estimated individual radiation dose was 80.5 mSv. Among 255 deaths overall (standardized mortality ratio [SMR] = 0.48; 95% confidence interval [CI] = 0.42-0.54) there were 76 cancer deaths (SMR = 0.56; CI = 0.43 - 0.74). Most cancer and cardiovascular SMRs were reduced. A slight increase was seen for brain cancer (SMR = 1.68; CI = 0.66-3.62). Employment duration was associated with the all-cancer mortality in Poisson regression analyses. No other dose-response relation was found. CONCLUSIONS: German cockpit crew have a low overall and cancer mortality. The role of occupational causes, and particularly cosmic radiation, appears limited.

Aerospace Medicine↗