Henrik Bøggild

Shift work, risk factors and cardiovascular disease

The literature on shift work, morbidity and mortality from cardiovascular disease, and changes in traditional risk factors is reviewed. Seventeen studies have dealt with shift work and cardiovascular disease risk. On balance, shift workers were found to have a 40% increase in risk. Causal mechanisms of this risk via known cardiovascular risk factors, in relation to circadian rhythms, disturbed sociotemporal patterns, social support, stress, behavior (smoking, diet, alcohol, exercise), and biochemical changes (cholesterol, triglycerides, etc) are discussed. The risk is probably multifactorial, but the literature has focused on the behavior of shift workers and has neglected other possible causal connections. In most studies methodological problems are present; these problems are related to selection bias, exposure classification, outcome classification, and the appropriateness of comparison groups. Suggestions for the direction of future research on this topic are proposed.

Shiftwork and cardiovascular disease: review of disease mechanisms.

This paper reviews the main findings concerning mechanisms explaining the increased risk of coronary heart disease (CHD) in shiftworkers. We discuss a conceptual model, in which three main shiftwork pathways to CHD are postulated--social problems, behavioral change, and disturbed circadian rhythm. Social problems that are associated with shiftwork might lead to stress. Significant shiftwork-related behavioral problems are smoking and unhealthy food habits. Disturbed circadian rhythm might result in sleep deprivation. Unphysiologic timing of physical activity and food intake in relation to circadian rhythms is another possible explanation for the negative impact on the cardiovascular system.

Shift work, social class, and ischaemic heart disease in middle aged and elderly men; a 22 year follow up in the Copenhagen Male Study.

OBJECTIVES: Shift work has been associated with an increased risk of ischaemic heart disease (IHD). Most published studies have had potential problems with confounding by social class. This study explores shift work as a risk factor for IHD after controlling for social class. METHODS: The Copenhagen male study is a prospective cohort study established in 1970-1 comprising 5249 men aged 40-59. Information obtained included working time, social class, and risk factors for IHD. A second baseline was obtained in 1985-6. The cohort was followed up for 22 years through hospital discharge registers for IHD, and cause of death was recovered from death certificates. RESULTS: One fifth of the cohort was shift working at entry with a significantly larger proportion of shift workers in lower social classes. Risk of IHD and all cause mortality over 22 years, adjusted for age only, for age and social class, and finally for age, social class, smoking, fitness, height, weight, and sleep disturbances, did not differ between shift and day workers. The relative risk of IHD, adjusted for age and social class was 1.0 (95% confidence interval (95% CI) 0.9-1.2). Men being shift workers in both 1971 and 1985 had the same risk as ex-shift workers in an 8 years follow up from the 1985-6 baseline. CONCLUSIONS: The present study questions shift work as an independent risk factor for IHD. The results of the study emphasise the importance of controlling adequately for the interplay of shift work and social class.

Shift work and subfecundity: a causal link or an artefact?

Aims: The Danish National Birth Cohort (DNBC) was used to examine whether shift work is associated with reduced fecundity as estimated by time to pregnancy (TTP). Methods: From 1 March 1998 to 1 May 2000, 39 913 pregnant women were enrolled in the DNBC. Data on job characteristics and TTP (0–2, 3–5, 6–12, and >12 months) were used for 17 531 daytime workers and 3907 shift workers who had planned the pregnancy. Fecundity odds ratios (ORs) were calculated with 95% confidence intervals using the discrete time survival analysis techniques performed by logistic regression. An OR above 1 expresses a shorter TTP and then a higher fecundity. Potential confounders, such as age at conception, gravidity, prepregnant body mass index, smoking, and alcohol consumption, as well as occupational characteristics, were also included in the model. Results: Fixed evening workers and fixed night workers had a longer TTP. Compared with daytime workers, the adjusted ORs were 0.80 (95% CI 0.70 to 0.92) for fixed evening workers, 0.80 (95% CI 0.63 to 1.00) for fixed night workers, 0.99 (95% CI 0.91 to 1.07) for rotating shift (without night) workers, and 1.05 (95% CI 0.97 to 1.14) for rotating shift (with night) workers. When analysis was restricted to nulliparous women, the estimates remained unchanged. The proportions of unplanned pregnancies and contraceptive failures were higher among fixed evening and fixed night workers. Conclusions: There was no unequivocal evidence of a causal association between shift work and subfecundity. The slightly reduced fecundity among fixed evening workers and fixed night workers may be mediated by pregnancy planning bias or differential options for sexual contacts.

Socioeconomic status and use of postmenopausal hormone replacement therapy among Danish women

Background.  Observational studies on hormone replacement therapy (HRT) have shown cardioprotective effects that have not been replicated in randomized controlled trials, perhaps due to unaccounted confounding by socioeconomic factors. To resolve this discrepancy, we examined the association between socioeconomic status (SES) and HRT use in a large population of Danish postmenopausal women.

Psychopathology, defence mechanisms, and the psychosocial work environment

Background: The body of evidence verifies the predictive value of certain work characteristics for mental health problems and that various levels of adaptation mechanisms are employed when dealing with adversity. Data on the relationships between employees’ mental health status, their perceptions of work, and their psychological defences are scarce. Aims: To examine the role that personal defences play in the relationship between psychiatric symptoms among working people and their working environment. Methods: Nine hundred and seventy six employees (mean age = 42.4 years, SD = 11.3) participated in a questionnaire study that included the Defence Style Questionnaire, the Symptom Checklist 90 revised, and the Copenhagen Psychosocial Questionnaire . Results: Data showed that greater maturity of psychological defences was associated with higher level of psychological functioning and there were strong associations between presence of psychopathology and the three defence clusters. Results indicated a strong positive correlation between the mature defence style and the perception of a satisfactory workplace. There was no interaction between psychopathology and defences in relation to work environment. Conclusion: Psychopathology and defences were significantly associated with work conditions, which could suggest that adaptation mechanisms and psychopathology are two independent forms of adjustment to the rapidly changing world of work.

The association between fluoride in drinking water and dental caries in Danish children. Linking data from health registers, environmental registers and administrative registers.

OBJECTIVES To study the association between fluoride concentration in drinking water and dental caries in Danish children. METHODS The study linked registry data on fluoride concentration in drinking water over a 10-year period with data on dental caries from the Danish National Board of Health database on child dental health for 5-year-old children born in 1989 and 1999, and for 15-year-old children born in 1979 and 1989. The number of children included in the cohorts varied between 41.000 and 48.000. Logistic regression was used to assess the correlations, adjusting for gender and taxable family income as a proxy variable for socioeconomic status. RESULTS   Fluoride concentration in drinking water varied considerably within the country from very low (<0.10 mg/l) to more than 1.5 mg/l. Only little variation was found over the 10-year study period. Dental caries in both 5-year-olds and 15-year-olds decreased over the study period. An inverse relation between the risk of dental caries and fluoride concentration in drinking water was found in both primary and permanent teeth. The risk was reduced by approximately 20% already at the lowest level of fluoride exposure (0.125-0.25mg/l). At the highest level of fluoride exposure (>1 mg/l), a reduction of approximately 50% was found. Similar findings were found if analysis was limited to children residing in the same place during the entire study period. CONCLUSIONS The study confirmed previous findings of an inverse relation between fluoride concentration in the drinking water and dental caries in children. This correlation was found in spite of the extensive use of fluoridated toothpaste and caries-preventive programs implemented by the municipal dental services in Denmark. Linking Danish health registers with environmental and administrative registers offers an opportunity for obtaining sample sizes large enough to identify health effect, which otherwise could not be identified.

Internal locus of control and choice in health service shift workers

This study examined the relationship between shift work-specific locus of control (SH-LOC), active choice of work schedule and health outcomes, personal initiatives and coping behaviours in 1611 Danish Health Service shift workers. The 20-item SH-LOC scale was administered as part of a battery of measures. Multivariate analysis of covariance (controlling for age, workplace experience and weekly work hours) tested for differential responses to shift working and coping strategies. Interactive effects of internality and type of work rota were examined. Higher internality was linked to better tolerance to shift work. This did not appear to be a result of greater personal action in higher internals. The importance of control as a potential moderating factor to shift work exposure and the possible use of this measure in the process of shift worker monitoring is highlighted.

Associations between follow-up screening after gestational diabetes and early detection of diabetes – a register based study

BackgroundWomen whose pregnancy was complicated by gestational diabetes have a 7-fold higher risk of developing diabetes, primarily type 2. Early detection can prevent or delay the onset of late complications, for which follow-up screening is important. This study investigated the extent of participation in follow-up screening and the possible consequences of nonattendance in the Region of North Jutland, Denmark.MethodIn Danish national registers covering the years 1994–2011 we identified 2171 birthing women whose pregnancy was complicated by first-time gestational diabetes. Control visits to general practitioners and biochemical departments after giving birth were charted. Following national guidelines we defined four intervals for assessment of participation in follow-up screening. Diagnosis of diabetes or treatment with glucose-lowering agents after giving birth were also identified. Participation in follow-up screening and risk of diabetes was calculated. Time to obtaining diagnosis of diabetes or initiating treatment was analysed by Cox regression models. All models were adjusted for age, ethnicity and income.ResultsHigh attendance was found during the first control interval, after which attendance decreased with time after giving birth for both controls at general practitioners and biochemical departments. All differences in proportions were statistically significant. Women attending controls at general practitioners had a significantly higher risk of diabetes diagnosis and treatment after gestational diabetes than women not attending. The results for women attending testing at biochemical departments also showed an increased risk of initiation of treatment. Women attending at least one general practitioners control had a significantly higher risk of early diabetes diagnosis or treatment. Time to initiation of treatment was significantly higher for testing at biochemical departments. Women with high incomes had a significantly lower risk of diabetes diagnosis or initiation of treatment compared to low-income women.ConclusionParticipation in follow-up screening after gestational diabetes is low in the North Denmark Region. Follow-up screening ensures early detection of diabetes and initiation of treatment. Our results emphasize the importance of development of interventions to improve early detection and prevention of diabetes after gestational diabetes.

Socioeconomic inequality and mortality - a regional Danish cohort study

BackgroundSocioeconomic inequalities in mortality pose a serious impediment to enhance public health even in highly developed welfare states. This study aimed to improve the understanding of socioeconomic disparities in all-cause mortality by using a comprehensive approach including a range of behavioural, psychological, material and social determinants in the analysis.MethodsData from The North Denmark Region Health Survey 2007 among residents in Northern Jutland, Denmark, were linked with data from nationwide administrative registries to obtain information on death in a 5.8-year follow-up period (1stFebruary 2007- 31stDecember 2012). Socioeconomic position was assessed using educational status as a proxy. The study population was assigned to one of five groups according to highest achieved educational level. The sample size was 8,837 after participants with missing values or aged below 30 years were excluded. Cox regression models were used to assess the risk of death from all causes according to educational level, with a step-wise inclusion of explanatory covariates.ResultsParticipants’ mean age at baseline was 54.1 years (SD 12.6); 3,999 were men (45.3%). In the follow-up period, 395 died (4.5%). With adjustment for age and gender, the risk of all-cause mortality was significantly higher in the two least-educated levels (HR = 1.5, 95%, CI = 1.2-1.8 and HR = 3.7, 95% CI = 2.4-5.9, respectively) compared to the middle educational level. After adjustment for the effect of subjective and objective health, similar results were obtained (HR = 1.4, 95% CI = 1.1-1.7 and HR = 3.5, 95% CI = 2.0-6.3, respectively). Further adjustment for the effect of behavioural, psychological, material and social determinants also failed to eliminate inequalities found among groups, the risk remaining significantly higher for the least educated levels (HR = 1.4, 95% CI = 1.1-1.9 and HR = 4.0, 95% CI = 2.3-6.8, respectively). In comparison with the middle level, the two highest educated levels remained statistically insignificant throughout the entire analysis.ConclusionSocioeconomic inequality influenced mortality substantially even when adjusted for a range of determinants that might explain the association. Further studies are needed to understand this important relationship.