Selective citation in scientific literature on the human health effects of bisphenol A.

INTRODUCTION: Bisphenol A is highly debated and studied in relation to a variety of health outcomes. This large variation in the literature makes BPA a topic that is prone to selective use of literature, in order to underpin one's own findings and opinion. Over time, selective use of literature, by means of citations, can lead to a skewed knowledge development and a biased scientific consensus. In this study, we assess which factors drive citation and whether this results in the overrepresentation of harmful health effects of BPA. METHODS: A citation network analysis was performed to test various determinants of citation. A systematic search identified all relevant publications on the human health effect of BPA. Data were extracted on potential determinants of selective citation, such as study outcome, study design, sample size, journal impact factor, authority of the author, self-citation, and funding source. We applied random effect logistic regression to assess whether these determinants influence the likelihood of citation. RESULTS: One hundred sixty-nine publications on BPA were identified, with 12,432 potential citation pathways of which 808 citations occurred. The network consisted of 63 cross-sectional studies, 34 cohort studies, 29 case-control studies, 35 narrative reviews, and 8 systematic reviews. Positive studies have a 1.5 times greater chance of being cited compared to negative studies. Additionally, the authority of the author and self-citation are consistently found to be positively associated with the likelihood of being cited. Overall, the network seems to be highly influenced by two highly cited publications, whereas 60 out of 169 publications received no citations. CONCLUSION: In the literature on BPA, citation is mostly driven by positive study outcome and author-related factors, such as high authority within the network. Interpreting the impact of these factors and the big influence of a few highly cited publications, it can be questioned to which extent the knowledge development in human literature on BPA is actually evidence-based.

Does diisocyanate exposure result in neurotoxicity?

CONTEXT: Diisocyanates have been associated with respiratory and dermal sensitization. Limited number of case reports, and a few case studies, media, and other references suggest potential neurotoxic effects from exposures to toluene diisocyanate (TDI), 1,6 hexamethylene diisocyanate (HDI), and methylene diisocyanate (MDI). However, a systematic review of the literature evaluating the causal association on humans does not exist to support this alleged association. OBJECTIVE: To perform systematic review examining the body of epidemiologic evidence and provide assessment of causal association based on principles of the Sir Austin Bradford Hill criteria or considerations for causal analysis. METHODS: A comprehensive search of public databases for published abstracts, case reports, cross-sectional surveys, and cohort studies using key search terms was conducted. Additional searches included regulatory reviews, EU IUCLID and EU Risk Assessment databases, and unpublished reports in the International Isocyanate Institute database. An expert panel consisting of physicians, toxicologists, and an epidemiologist critically reviewed accepted papers, providing examination of epidemiologic evidence of each report. Finally, the Hill criteria for causation were applied to the summative analysis of identified reports to estimate probability of causal association. RESULTS: Twelve papers reporting exposed populations with a variety of neurological symptoms or findings suitable for analysis were identified, including eleven case or case series reports, and one cross-sectional study. Three papers reported on the same population. Each of the papers was limited by paucity of diisocyanate exposure estimates, the presence of confounding exposures to known or suspected neurotoxicants, a lack of objective biological measures of exposure or neurotoxic effects, and lack of relative strength of association measures. Additionally, reported health symptoms and syndromes lacked consistency or specificity. No plausible mechanism of toxicity was found. Application of a predictive mathematical model for determining probability of causal association for neurotoxicity was calculated to be 21%. CONCLUSION: There is insufficient evidence for a causal association of neurotoxic effects and diisocyanate exposure based on lack of evidence in all categories of the Hill criteria for causality except for temporal association of reported symptoms and alleged exposure. Future reports should attempt to address more rigorous exposure assessment and control for confounding exposures.

The healthy worker effect in US chemical industry workers.

BACKGROUND: Occupational studies typically observe a 20% deficit in overall mortality, broadly characterized as the healthy worker effect (HWE). Components of the HWE may be addressed by various analytical approaches. AIMS: To explore the HWE in a modern industrial cohort. METHODS: Standardized mortality ratios (SMRs) were calculated for 114,683 US chemical industry employees, who worked at least 3 days between 1960 and 2005. RESULTS: SMRs were 79 (95% confidence interval 78-80) for all causes, 81 (95% confidence interval 79-82) for heart disease, 70 (95% confidence interval 67-73) for non-malignant respiratory disease, 83 (95% confidence interval 81-85) for smoking-related cancers (buccal, cervix, oesophagus, stomach, pancreas, lung, larynx, bladder and kidney) combined and 97 (95% confidence interval 95-100) for other cancers. CONCLUSIONS: The low SMRs observed in this study are likely due to differential smoking between the cohort and the background population. Future considerations to control for the HWE should take this into account.

Work-family conflict as a risk factor for sickness absence.

OBJECTIVES: (1) To study both cross-sectional and prospective relationships between work-family conflict and sickness absence from work; (2) to explore the direction of the relationships between the different types of conflict (work-home interference and home-work interference) and sickness absence; and (3) to explore gender differences in the above relationships. METHODS: Data from the Maastricht Cohort Study were used with six months of follow up (5072 men and 1015 women at T6). Work-family conflict was measured with the Survey Work-Home Interference Nijmegen (SWING). Sickness absence was assessed objectively through individual record linkage with the company registers on sickness absence. RESULTS: In the cross-sectional analyses, high levels of work-family conflict, work-home interference, and home-work interference were all associated with a higher odds of being absent at the time of completing the questionnaire, after controlling for age and long term disease. Differences in average number of absent days between cases and non-cases of work-home interference were significant for men and most pronounced in women, where the average number of absent days over six months follow up was almost four days higher in women with high versus low-medium work-home interference. CONCLUSIONS: A clear relation between work-family conflict and sickness absence was shown. Additionally, the direction of work-family conflict was associated with a different sickness absence pattern. Sickness absence should be added to the list of adverse outcomes for employees struggling to combine their work and family life.

Prediction of sickness absence: development of a screening instrument.

OBJECTIVES: To develop a concise screening instrument for early identification of employees at risk for sickness absence due to psychosocial health complaints. METHODS: Data from the Maastricht Cohort Study on "Fatigue at Work" were used to identify items to be associated with an increased risk of sickness absence. The analytical procedures univariate logistic regression, backward stepwise linear regression, and multiple logistic regression were successively applied. For both men and women, sum scores were calculated, and sensitivity and specificity rates of different cut-off points on the screening instrument were defined. RESULTS: In women, results suggested that feeling depressed, having a burnout, being tired, being less interested in work, experiencing obligatory change in working days, and living alone, were strong predictors of sickness absence due to psychosocial health complaints. In men, statistically significant predictors were having a history of sickness absence, compulsive thinking, being mentally fatigued, finding it hard to relax, lack of supervisor support, and having no hobbies. A potential cut-off point of 10 on the screening instrument resulted in a sensitivity score of 41.7% for women and 38.9% for men, and a specificity score of 91.3% for women and 90.6% for men. CONCLUSIONS: This study shows that it is possible to identify predictive factors for sickness absence and to develop an instrument for early identification of employees at risk for sickness absence. The results of this study increase the possibility for both employers and policymakers to implement interventions directed at the prevention of sickness absence.

A framework for using epidemiological data for risk assessment.

Data on health effects from human exposure to chemicals provide the most direct information for risk assessment. Despite their clear relevance for risk assessment and despite the frequently made statements by regulatory bodies to use epidemiological data whenever deemed appropriate, they are not always optimally used. In this article, a framework for using epidemiological data in risk assessment is presented. Before using an epidemiologic study as the basis for risk assessment, its quality must be evaluated. The quality criteria for such a study strongly depends on the type of association between the chemical and health effect in terms of its specificity and latency period. The framework is built on the type of health effect under consideration, whether it is a specific or non-specific effect and time window of the effect, whether it is an acute, sub-acute or long-term effect. Specificity and latency are aspects that have a great impact on the choice of research design and quality criteria that must be met in order to produce reliable results appropriate for risk assessment purposes. Although expert judgement will always play an important role, the framework can help to assess if a set of epidemiological data are sufficiently reliable to serve as the basis for the derivation of health-based exposure limits. The limitations and suitability to use for risk assessment of epidemiologic studies is more likely to be the result of poor or insufficient exposure data than of poor or unreliable health effect information. It is concluded that the value of epidemiologic data not only depends on its intrinsic quality, but also on the type of health effects under consideration. In this respect, the specificity and latency play an important role.

Radiation exposure and cause specific mortality among nuclear workers in Belgium (1969-1994).

Cause specific mortality was studied in nuclear workers from five nuclear facilities in Belgium and compared to the general population. For the 1969-1994 period, mortality in male nuclear workers is significantly lower for all causes of death and for all cancer deaths. The same conclusions are reached if one assumes a latency period of 20 y between the first irradiation and cancer induction. In female workers, mortality due to all causes and all cancer deaths is not different from that of the general population. Analysis of cause specific mortality was performed for male and female workers for three endpoints: specific cancer sites, cardiovascular and respiratory diseases. No significant increase in mortality was observed. In male workers, the influence of cumulative dose was also investigated using four dose levels: no significant correlation was found. Smoking habits may be a confounding factor in smoking related health conditions.

Organizational characteristics as predictors of work disability: a prospective study among sick employees of for-profit and not-for-profit organizations.

INTRODUCTION: This article reports a prospective study that focused on the influence of organizational structure and organizational culture on the outcome of sickness absence, return to work or work disability. Former studies of determinants of work disability hardly have given attention to organizational characteristics and, if so, not following a appropriate prospective design. METHODS: The study population consisted of 455 employees of 45 for-profit and not-for-profit companies participating in the Maastricht Cohort Study on fatigue at work who were on sick leave for at least 6 weeks. Both independent variables which were type of company, size, centralization of decision making and organizational culture, and covariates, which were sex, age, educational level, fatigue, and chronic illness, were all measured before employees reported sick. The dependent variable outcome of the sickness absence, mainly return to work or work disability, was measured 15 months after reporting sick. RESULTS: Multilevel logistic regression analysis, with organizational characteristics as level 2 independent variables and demographic and health characteristics as covariates, suggested that the type of company (for-profit/private or not-for-profit/public) is predictive of the outcome of sickness absence (crude OR = 2.21; CI: 1.16-4.20), but this may be partially due to a higher proportion of fatigued and chronically ill employees in not-for-profit companies (adjusted OR = 2.09; CI: 0.93-4.37). Findings about the role of some other organizational characteristics, like organizational culture, were inconclusive. CONCLUSIONS: Organizational characteristics should next to health characteristics be included in the models of studies which aim at predicting which sick employees are at risk for work disability. To prevent work disability not-for-profit companies might be stimulated to more active return-to-work policy by charging them with the costs of it.

Trends in the prevalence of respiratory symptoms and treatment in Dutch children over a 12 year period: results of the fourth consecutive survey.

BACKGROUND: Although there is considerable evidence that the prevalence of childhood asthma has increased over the last decades, it is not clear if this trend is still ongoing. A study was undertaken to investigate whether previously observed trends in the prevalence of respiratory symptoms, physician visits, medication use, and absence from school in Dutch children aged 8-9 years persisted in 2001. METHODS: Parents of 1154 children aged 8-9 years eligible for a routine physical examination in 2001 were asked to complete a questionnaire on the respiratory health of their child. RESULTS: In 2001, 1102 children (95.5%) participated in the survey. Similarly high response rates were obtained in the surveys of 1989, 1993 and 1997, with 1794, 1526 and 1670 children aged 8-9 years participating in the respective surveys. The decreasing trend previously observed for recent wheeze between 1989 and 1997 persisted into 2001, particularly in boys. After increasing between 1989 and 1997, the prevalence of shortness of breath with wheeze decreased between 1997 and 2001. The proportion of wheezy children using medication increased between 1989 and 2001 in boys (42.9% v 64.8%; p = 0.003), but the increase was not statistically significant in girls (34.0% v 45.7%; p = 0.096). CONCLUSION: The prevalence of recent wheeze in Dutch school children has declined steadily since 1989. The rising prevalence of medication use in symptomatic children over time may reflect better asthma control and may partly explain the concurrently decreasing trend in the prevalence of asthma symptoms in our study population.

Differences in asthma diagnosis and medication use in children living in Germany and the Netherlands.

AIM: To compare diagnosis and treatment between German and Dutch children with asthmatic symptoms at the age of 5-6 and 7-8 years, and the use of anti-asthma medication at 7-8 years of age. METHODS: Parents of 4462 children participated in two surveys, in 1995 and 1997. All 465 children identified with current asthmatic symptoms at the age of 5-6 (May 1995) or at 7-8 years of age (May 1997) were sent a third more detailed questionnaire (October 1997). RESULTS: Asthma diagnosis was more prevalent in Dutch children with current asthmatic complaints (50-60%), whereas over 90% of the German children with current asthmatic complaints had been diagnosed with bronchitis. Inhaled beta(2)-agonists were more frequently used by Dutch children compared to German children (67.3% vs. 45.6% p < 0.01) as were inhaled steroids (38.9% vs. 7.0% p < 0.01). Instead, German children more often used sodium cromoglycate or nedocromil as anti-inflammatory medication as compared with Dutch children (42.1% vs. 11.5% p < 0.01). CONCLUSIONS: Differences in diagnosis rates for asthma and bronchitis between German and Dutch children most likely result from differential labelling of complaints, and probably lead to differences in treatment practice, indicating possible undertreatment of German children with inhaled steroids.

Seeking help in relation to work--visiting the occupational physician or the general practitioner.

BACKGROUND: It has not yet been examined whether employees with health or work problems prefer visiting the Occupational Physician (OP) or the General Practitioner (GP). AIM: Examining whether health and work problems predict visiting the OP or GP. METHOD: Multiple regression analyses within a prospective cohort study. RESULTS: None of the predictors was exclusively associated with visiting the OP, while emotional work demands and work-family conflict were associated with visiting the GP in relation to work. CONCLUSIONS: OPs might wish to clarify their preventive role to employees.

Infant immunization and the occurrence of atopic disease in Dutch and German children: a nested case-control study.

Our goal was to assess the role of early childhood vaccination in the occurrence of respiratory symptoms and allergic sensitization in 7-8-year-old Dutch and German children. A nested case-control study was conducted among children participating in a large longitudinal study on respiratory health, to study the relationship between vaccination (bacille Calmette-Guérin (BCG), pertussis, measles/mumps, rubella, and Haemophilus influenza type b (Hib)) and respiratory symptoms and allergic sensitization. Parents of 510 7-8-year-old children with respiratory complaints and an equal number of randomly selected children without respiratory complaints were asked to complete a questionnaire. Blood samples were collected for specific serum IgE analysis. Vaccination status was assessed through the records of the participating Municipal Health Services. No association between vaccination against pertussis, measles, rubella, or Hib and respiratory symptoms or allergic sensitization was found. For sensitization against house dust mite, BCG vaccination resulted in an increased risk (OR, 2.28; 95% CI, 1.05-4.96). Birth order was inversely associated with allergic sensitization, but was not related to respiratory symptoms. We found an association between BCG vaccination and the subsequent risk for sensitization against house dust mite. No evidence was found for an association between vaccination and respiratory symptoms. Earlier reports of an association of birth order with atopic disease were supported by the results of the present study.

Anxiety and depression in the working population using the HAD Scale--psychometrics, prevalence and relationships with psychosocial work characteristics.

BACKGROUND: The purposes of this study were: 1) to explore the psychometric properties of the HAD Scale in the working population, 2) to determine the prevalence of anxiety and depression on two severity levels among employees, and 3) to examine whether psychosocial work-related determinants for both categories of mental health problems may differ. METHODS: Data were taken from 7482 employees participating in the epidemiological Maastricht Cohort Study on Fatigue at Work. Anxiety and depression were measured with the easy to administer self-report Hospital Anxiety and Depression (HAD) Scale, while several questionnaires and self-formulated questions were used to measure psychosocial work-related characteristics. RESULTS: A principal component analysis indicated that the HAD Scale enables measuring anxiety and depression as separate constructs among employees. On a subclinical level, prevalences of anxiety and depression were both considerable: anxiety prevalences were 8.2 % for males and 10 % for females, and depression prevalences were 7.1% for males and 6.2% for females. Regarding self-reported psychosocial work characteristics, in multivariate regression analyses partly differential cross-sectional associations were found for anxiety and depression. CONCLUSIONS: The results indicate that subclinical anxiety and depression are considerable in the working population and provide suggestive evidence that diagnosing, preventing or managing anxiety and depression among employees may require focusing on different aspects of their psychosocial work environment.

Psychosocial work characteristics as risk factors for being injured in an occupational accident.

The aim of this study was to investigate the relationship between psychosocial work characteristics and the risk for being injured in an occupational accident. We performed this study within the framework of the Maastricht Cohort Study of Fatigue at Work, a prospective cohort study on employees (n = 7051) from a wide range of companies and organizations. One hundred eight workers reported being injured in an occupational accident for which the subject consulted a physician or physiotherapist. Adjustments were made for work environment and demographic variables. High psychologic job demands were a risk factor for being injured in an occupational accident. Low decision latitude had a crude relative risk for being injured in an occupational accident of 2.02 (95% confidence interval [CI] = 1.23-3.39). This relationship almost completely disappeared after adjustment for the confounders mentioned here. Coworker and supervisor support were inversely related to the risk of being injured in an occupational accident but did not reach statistical significance. Other psychosocial work characteristics that had a significant effect on the risk for being injured in an occupational accident were conflicts with the supervisor (relative risk [RR] = 2.49; 95% CI = 1.42-4.37) or colleagues (RR = 2.62; 95% CI = 1.58-4.35), job satisfaction (RR = 1.43; 95% CI = 1.08-1.91), and high emotional demands (RR = 2.45; 95% CI = 1.52-3.94). We conclude that after adjustment for demographic variables, fatigue, and factors that describe the type of work environment that high psychologic job demands, emotional demands, and conflicts with the supervisor and/or colleagues are risk factors for being injured in an occupational accident.

Prevalence of chronic fatigue syndrome-like caseness in the working population: results from the Maastricht cohort study.

AIM: To determine the prevalence of chronic fatigue syndrome (CFS)-like caseness in the working population. METHODS: Using data from the prospective Maastricht Cohort Study on Fatigue at Work, the prevalence and incidence of CFS-like cases (employees meeting research criteria for CFS) were determined among 5499 employees who responded to the follow up assessment 3 years and 8 months after baseline. RESULTS: Of the 5499 employees, 199 (3.6%) were identified as CFS-like cases. By deleting possible CFS-like cases at baseline, the annual incidence of CFS-like caseness was estimated to be 85 per 10 000. Twenty employees (0.36%) reported having been diagnosed with CFS by a physician. CONCLUSIONS: The prevalence of CFS-like cases (3.6%) was considerably higher than the prevalence of CFS reported in previous studies (0.006-3%). These findings suggest that the CFS-like caseness may be underdetected in the working population and perhaps in other populations as well.

An epidemiological approach to study fatigue in the working population: the Maastricht Cohort Study.

In 1998, a large scale prospective cohort study of prolonged fatigue in the working population was started in the Netherlands. The ultimate goal of this Maastricht Cohort Study was to identify risk factors involved in the aetiology and natural course of prolonged fatigue in the working population and to develop preventive measures and treatments that can be used in occupational health settings. In this paper, a conceptual model for epidemiological research on prolonged fatigue is presented. This model is the basis for the Maastricht Cohort Study. Alongside the model and design, the characteristics of the study population, the prevalence and one year cumulative incidence of prolonged fatigue, as well as its relation with secondary health outcomes (psychological distress, need for recovery, and burnout) are presented. Furthermore, model, design, and the presented results are discussed.

Fatigue as a predictor of sickness absence: results from the Maastricht cohort study on fatigue at work.

OBJECTIVES: To investigate whether there is a relationship between fatigue and sickness absence. Two additional hypotheses were based on the theoretical distinction between involuntary, health related absence and voluntary, attitudinal absence. In the literature, the former term is usually used to describe long term sickness absence, the latter relates to short term sickness absence. In line with this, the first additional hypothesis was that higher fatigue would correspond with a higher risk of long term, primarily health related absence. The second additional hypothesis was that higher fatigue would correspond with a higher risk of short term, primarily motivational absence. METHODS: A multidimensional fatigue measure, as well as potential sociodemographic and work related confounders were assessed in the baseline questionnaire of the Maastricht cohort study on fatigue at work. Sickness absence was objectively assessed on the basis of organisational absence records and measured over the six months immediately following the baseline questionnaire. In the first, general hypothesis the effect of fatigue on time-to-onset of first sickness absence spell during follow up was investigated. For this purpose, a survival analysis was performed. The effect of fatigue on long term sickness absence was tested by a logistic regression analysis. The effect of fatigue on short term sickness absence was investigated by performing a survival analysis with time-to-onset of first short absence spell as an outcome. RESULTS: It was found that higher fatigue decreased the time-to-onset of the first sickness absence spell. Additional analyses showed that fatigue was related to long term as well as to short term sickness absence. The effect of fatigue on the first mentioned outcome was stronger than the effect on the latter outcome. Potential confounders only weakened the effect of fatigue on long term absence. CONCLUSIONS: Fatigue was associated with short term but particularly with long term sickness absence. The relation between fatigue and future sickness absence holds when controlling for work related and sociodemographic confounders. Fatigue as measured with the Checklist Individual Strength can be used as a screening instrument to assess the likelihood of sickness absence in the short term.

Need for recovery after work and the subsequent risk of cardiovascular disease in a working population.

BACKGROUND: A high need for recovery after work can be regarded as a short term adverse effect of working day stressors and the person's inability to cope and recover. Consequently, it might be an intermediate factor between job stressors and cardiovascular disease (CVD). AIM: To investigate, in a longitudinal study, the relation between need for recovery and subsequent CVD. METHODS: Data from the Maastricht Cohort Study of 12 140 workers were used, with 42 incident self reported CVD cases during 32 months of follow up. Cox proportional hazards analysis was used to calculate age, gender, smoking status, and educational level adjusted relative risks. RESULTS: The adjusted relative CVD risk for the second compared to the first tertile of the need for recovery score was 1.22 (95% CI: 0.49 to 3.04), and for the third compared to the first tertile was 3.16 (95% CI: 1.34 to 7.48). When need for recovery was entered as continuous score, an adjusted relative risk per SD increase of 1.54 (95% CI: 1.15 to 2.03) was found. Additional adjustment for several work related factors as job demands, did not notably change the observed relation between need for recovery and CVD. Moreover, the increased risk for subjects reporting high job demands (1.38 per SD increase; 95% CI: 1.02 to 3.92) decreased substantially after adjustment for need for recovery. CONCLUSION: The results show that need for recovery is a strong predictor of subsequent cardiovascular disease and might be an intermediate factor between job stressors and cardiovascular disease.