Night and shift work patterns and incidence of type 2 diabetes and hypertension in a prospective cohort study of healthcare employees.

OBJECTIVES: This study aimed to evaluate effects of night and shift work patterns on type 2 diabetes (T2D) and hypertension in a longitudinal study, with detailed information on working hours. METHODS: The cohort comprised about 28 000 nurses and nursing assistants employed for more than one year 2008-2016 in Stockholm, Sweden. The employee register held detailed individual information on daily working hours. Information on diagnoses came from national and regional registers. Hazard ratios (HR) and confidence intervals (CI) were estimated by discrete-time proportional hazard models, adjusting for sex, age, country of birth, and profession. RESULTS: During follow-up in 2013-2017, we identified 232 cases of T2D and 875 of hypertension. We observed an increased risk of T2D, but not hypertension, among employees who worked only night shifts the previous year (HR 1.59, 95% CI 1.02-2.43) and those with intensive shift work (>120 afternoon and/or night shifts the previous year: HR 1.67, 95% CI 1.11-2.48) compared to only day work. There was a non-significantly increased risk of T2D related to mixed day and afternoon shifts (HR 1.34, 95% CI 0.97-1.88). We observed tendencies in increased risk of T2D related to frequent spells of ≥3 consecutive night shifts and with number of years with exclusive (but not mixed) night work. CONCLUSIONS: Permanent night work and frequent afternoon and/or night shifts were associated with an increased risk of T2D the following year, but not hypertension. The T2D risk was, to some extent, affected by frequent spells of several night shifts in a row and by cumulative years with permanent night work.

Night work and breast cancer risk in a cohort of female healthcare employees in Stockholm, Sweden.

OBJECTIVES: Night work has been classified as probably carcinogenic to humans by the International Agency for Research on Cancer, but epidemiological evidence was considered limited due to variability in findings and potential bias. This study aimed to investigate the risk of breast cancer in a cohort with detailed and registry-based data on night work. METHODS: The cohort comprised 25 585 women (nurses and nursing assistants) employed 1 year or more between 2008 and 2016 in the healthcare sector in Stockholm. Information on work schedules was obtained from employment records. Breast cancer cases were identified from the national cancer register. HRs were estimated by a discrete time proportional hazards model, adjusting for age, country of birth, profession and childbirth. RESULTS: There were 299 cases of breast cancer, 147 in premenopausal and 152 in postmenopausal women. The adjusted HR of postmenopausal breast cancer in association with ever versus never working nights was 1.31 (95% CI 0.91 to 1.85). Eight or more years of night work was associated with an increased risk of postmenopausal breast cancer, HR=4.33 (95% CI 1.45 to 10.57), based on five cases only, though. CONCLUSIONS: This study is limited by a short period of follow-up and a lack of information on night work before 2008. Most exposure metrics showed no association with breast cancer risk, but there was an elevated risk of postmenopausal breast cancer in women after 8 or more years of night work.

Night and shift work characteristics and incident ischemic heart disease and atrial fibrillation among healthcare employees - a prospective cohort study.

OBJECTIVE: This study aimed to examine the effects of various aspects of night and shift work on the risk of incident ischemic heart disease (IHD) and atrial fibrillation (AF) using detailed and registry-based exposure data. METHODS: This prospective cohort study included >30 300 healthcare employees (eg, nurses, nursing assistants) employed for at least one year in Region Stockholm 2008-2016. Information on daily working hours was obtained from a computerized administrative employee register and outcomes from national and regional registers. Using discrete-time proportional hazard models, we analyzed the outcomes as functions of working hour characteristics the preceding year, adjusted for sex, age, country of birth, education, and profession. RESULTS: We observed 223 cases of IHD and 281 cases of AF during follow-up 2009-2016. The risk of IHD was increased among employees who the preceding year had permanent night shifts compared to those with permanent day work [hazard ratio (HR) 1.61, 95% confidence interval (CI) 1.06-2.43] and among employees working night shifts >120 times per year compared to those who never worked night (HR 1.53, 95% CI 1.05-2.21). When restricted to non-night workers, the risk of IHD was increased for employees having frequent quick returns from afternoon shifts. No increased risks were observed for AF. CONCLUSIONS: Night work, especially working permanent night shifts and frequent night shifts, is associated with an increased risk of incident IHD but not AF. Moreover, frequent quick returns from afternoon shifts (among non-night workers) increased IHD risk. Organizing work schedules to minimize these exposures may reduce IHD risk.

Shift and night work during pregnancy and preterm birth-a cohort study of Swedish health care employees.

BACKGROUND: Previous studies of preterm birth (PTB) concerning night work have been inconclusive and partly limited by imprecise data on working schedules. This study investigated the risk of PTB in relation to detailed, registry-based data on working hours. METHODS: In a register-based prospective cohort study, we identified 4970 singleton births with information on PTB from the Swedish Medical Birth Register of health care employees in Stockholm. Day-by-day information on working hours 2008-16 was obtained from a computerized employee register. Odds ratios (ORs) of PTB according to work hour characteristics were analysed by logistic regression adjusted for mother's age, stature, body mass index (BMI), parity, smoking habits, education, profession and country of birth. RESULTS: There was an increased risk of PTB among those who frequently worked night shifts (>25 times) [OR, 1.62; 95% confidence interval (CI), 1.03-2.53] and who ever worked ≥3 consecutive night shifts (OR, 1.43; 95% CI, 1.03-1.99) during the first trimester. Frequently (> 8 times) working 3 or more consecutive nights, and frequently (>18 times) having quick returns from night shifts (<28 h) during the first trimester showed 3-4 fold increased risk of PTB. Moreover, working frequent (>20 times) long shifts (≥10 h) (OR 1.63; 95% CI, 1.07-2.49) during the first trimester and working any Week >40 h (OR 2.05; 95% CI, 1.31-3.22) during the third trimester were associated with PTB. CONCLUSIONS: In this cohort of Swedish health care employees with registry-based data on working hours, night work, especially working frequent consecutive nights, and quick returns from night shifts during the first trimester were associated with increased risk of PTB among pregnant women.

Night and shift work and incidence of cerebrovascular disease - a prospective cohort study of healthcare employees in Stockholm.

OBJECTIVE: This study aimed to investigate the effects of various aspects of night and shift work regarding incident cerebrovascular disease (CeVD). METHODS: The cohort included 26 667 women and 3793 men (nurses and nursing assistants) who were employed for at least one year 2008-2016 in Region Stockholm, Sweden. Information about the cohort and working hours were obtained from a computerized employee-register and diagnoses were retrieved from national and regional registers. We used discrete time proportional hazard models to assess the risk of CeVD (2009-2017), in relation to work hour characteristics, adjusting for sex, age, country of birth, education and profession. RESULTS: We observed an excess risk of CeVD (N=223) among employees who, during the preceding year, worked night shifts >30 times [hazard ratio (HR) 1.44, 95% confidence interval (CI) 1.04-1.99] or ≥3 consecutive night shifts >15 times (HR 1.69, 95% CI 1.18-2.42) or with >30 quick returns (<28 hours) from night shifts (HR 1.52, 95% CI 1.10-2.10) compared to those who did not work nights. We also observed an excess risk among employees with a long duration (>5 years) of exposure to night shift work (HR 1.87, 95% CI 1.27-2.77), all supported by a dose-response pattern. CONCLUSIONS: Our results show that the risk of CeVD among nurses and nursing assistants is associated with night shift work. The number of years with night shift work, the frequency of night shifts per year, the frequency of consecutive night shifts, and short recovery after night shifts influenced the risk. Work schedules aiming at minimizing these aspects of night shift work may reduce the risk.

Cancer incidence among Swedish firefighters: an extended follow-up of the NOCCA study.

OBJECTIVES: To evaluate cancer incidence among Swedish firefighters and analyze risk in relation to work duration as a proxy for cumulative exposure. METHODS: This cohort study is based on the Swedish component of the Nordic Occupational Cancer (NOCCA) project. The cohort includes six million people who participated in one or more of the population censuses in 1960, 1970, 1980 and 1990. The census data were linked to the Swedish Cancer Registry for the 1961-2009 period, extending a previous NOCCA follow-up time by 4 years. We identified 8136 male firefighters. SIRs were calculated using cancer incidence rates in the national population as a reference. RESULTS: We found a statistically significant excess of non-melanoma skin cancer (SIR = 1.48, 95% CI 1.20-1.80) but no positive relationship between risk and work duration. There was a small, yet statistically significant increased risk of prostate cancer among firefighters with service times of 30 years or more. The first follow-up period (1961-1975) showed an increased risk of stomach cancer relative to the reference group, while the last period (1991-2009) showed an increased risk of non-melanoma skin cancer. There was no excess risk for all cancer sites combined (SIR = 1.03, 95% CI 0.97-1.09). CONCLUSIONS: Our results do not support an overall risk of cancer among Swedish firefighters, but a possible risk of non-melanoma skin cancer exists. The previously noted excess of prostate cancer among Swedish firefighters in NOCCA was no longer statistically significant in this extended follow-up but was present among those with the longest service times.

Airborne and Dermal Exposure to Polycyclic Aromatic Hydrocarbons, Volatile Organic Compounds, and Particles among Firefighters and Police Investigators.

AIMS: The main aim of this study was to assess dermal exposure to polycyclic aromatic hydrocarbons (PAHs) and airway exposure to PAHs, volatile organic compounds (VOCs; benzene and 1,3-butadiene), and particles among firefighters (FFs) and police forensic investigators (PFIs) in Sweden. METHODS: Active (pump with a filter and sorbent tube) and passive (polyurethane foam -cyl and perkin elmer carbopack-tube) personal air sampling and dermal tape stripping (wrist and collar bone) were performed on seven FF team leaders during training fires and nine PFIs investigating the aftermath of live fire events. In addition, passive personal air sampling was performed on eight FF team leaders during live emergency fires. PAHs and VOCs were analysed using high-resolution gas chromatography low-resolution mass spectrometry. The mass concentration of total dust (particles) was determined using standard gravimetric methods. RESULTS: The air samples showed that the exposure to PAHs, benzene, 1,3-butadiene, and particles was below Swedish occupational exposure limits (OELs). Naphthalene was the predominant PAH in all air samples. Benzene and 1,3-butadiene were more abundant in live emergency fires, which caused higher exposures than the other studied situations. Both gaseous- and particle-associated PAHs were present on skin. The wrists seemed to be less well protected than the collarbone area. CONCLUSIONS: FFs and PFIs are exposed to several hazardous compounds during their work. Air exposures varied considerably between working scenarios. The observed exposures were substantially higher than urban background levels but well below Swedish OELs. The measured dermal PAH exposures were comparable to previously reported doses for US FFs but lower than the exposures reported for Swedish chimney sweeps.

An improved method for determining dermal exposure to polycyclic aromatic hydrocarbons.

Many workers are occupationally exposed to polycyclic aromatic hydrocarbons (PAHs), which may cause various health problems, and some PAHs are known or suspected carcinogens. PAH exposure is primarily monitored by air sampling, but contamination may also occur through dermal exposure. PAHs adsorbed to the skin can be sampled by tape-stripping, but subsequent extraction of sampling tapes in organic solvent also releases diverse co-eluting substances that are difficult to remove before analysis of the PAHs by gas chromatography/mass spectrometry (GC/MS). The objective of this study was to optimise a procedure for analytical clean-up after extraction of 32 PAHs from tape-strips, by dialysis in organic solvent using semipermeable membranes. With triplicate subsamples, the developed method yields acceptable precision and repeatability for both the 32 PAHs, across the concentration range 10-160 ng per sample, and for a certified reference material (urban dust). The optimized clean-up procedure and GC/MS methodology was used to assess PAHs on skin from the lower part of the ventral side of the wrist and just below the collar bone of three firefighters and seven controls (office workers). Several gaseous and particle-bound PAHs were detected in all samples, including controls. Thus, the optimized procedure using semipermeable membranes for clean-up of tape-strip extracts can be used to assess the dermal exposure of both occupational and general populations to multiple PAHs. The results also show that both gaseous and particle-bound PAHs, including alkylated species, may be present on skin.

Evaluation of polyurethane foam passive air sampler (PUF) as a tool for occupational PAH measurements.

Routine monitoring of workplace exposure to polycyclic aromatic hydrocarbons (PAHs) is performed mainly via active sampling. However, active samplers have several drawbacks and, in some cases, may even be unusable. Polyurethane foam (PUF) as personal passive air samplers constitute good alternatives for PAH monitoring in occupational air (8 h). However, PUFs must be further tested to reliably yield detectable levels of PAHs in short exposure times (1-3 h) and under extreme occupational conditions. Therefore, we compared the personal exposure monitoring performance of a passive PUF sampler with that of an active air sampler and determined the corresponding uptake rates (Rs). These rates were then used to estimate the occupational exposure of firefighters and police forensic specialists to 32 PAHs. The work environments studied were heavily contaminated by PAHs with (for example) benzo(a)pyrene ranging from 0.2 to 56 ng m-3, as measured via active sampling. We show that, even after short exposure times, PUF can reliably accumulate both gaseous and particle-bound PAHs. The Rs-values are almost independent of variables such as the concentration and the wind speed. Therefore, by using the Rs-values (2.0-20 m3 day-1), the air concentrations can be estimated within a factor of two for gaseous PAHs and a factor of 10 for particulate PAHs. With very short sampling times (1 h), our method can serve as a (i) simple and user-friendly semi-quantitative screening tool for estimating and tracking point sources of PAH in micro-environments and (ii) complement to the traditional active pumping methods.

Cancer incidence in Stockholm firefighters 1958-2012: an updated cohort study.

OBJECTIVES: Previous studies on firefighters indicate an increased risk of cancer although findings regarding which cancer sites are in excess have been inconsistent. The aim of this study was to investigate the cancer incidence among Swedish firefighters. METHODS: This updated cohort study included 1080 men who worked at least 1 year as a firefighter in the city of Stockholm, Sweden during 1931-1983. First-time diagnoses of cancer were identified through the Swedish Cancer Registry from 1958 until 2012. Employment as a firefighter was determined from the annual fire station enrolment records. Standardized incidence ratios were calculated using the Stockholm population as reference. RESULTS: Firefighters in Stockholm had a low overall risk of cancer (SIR = 0.81 95% CI 0.71-0.91). However, firefighters were at an increased risk of stomach cancer (SIR = 1.89 95% CI 1.25-2.75). Firefighters had significantly low risks for prostate cancer (SIR = 0.68 95% CI 0.52-0.87) and malignant melanoma of the skin (SIR = 0.30 95% CI 0.06-0.88). There was a statistically significant trend of increasing overall risk of cancer with increasing employment duration, although there was still no excess of cancer overall in any of the categories of employment duration. CONCLUSION: Stockholm firefighters had an increased risk of stomach cancer but a low overall risk of cancer. The trend of increasing overall risk of cancer with increasing employment duration could potentially be related to the carcinogenic exposures at work.

Exposure to Particles, Polycyclic Aromatic Hydrocarbons, and Nitrogen Dioxide in Swedish Restaurant Kitchen Workers.

AIMS: The aim of this study was to measure the exposure to total dust, polycyclic aromatic hydrocarbons (PAHs), and nitrogen dioxide (NO2) of kitchen workers in four different types of restaurants in Sweden (Large scale, European, Fast food, and Asian). METHODS: One hundred full work-shift (8 h) personal exposure samples were taken from 36 workers in 21 commercial kitchens. Most workers were sampled three times. Mass concentration of total dust was determined using standard gravimetric methods; the filters were analyzed for their content of particulate PAHs. Gas-phase PAHs were sampled using adsorbent tubes (XAD-II) placed after the filter and analyzed with high-resolution gas chromatography/low-resolution mass spectrometry. NO2 was measured using passive dosimeters. Stationary measurements in the kitchen were made in parallel with the personal sampling. RESULTS: Group geometric mean concentrations for personal exposure to total dust ranged from 77 µg m-3 (Fast food) to 320 µg m-3 (European kitchens). Individual exposure samples of total dust ranged from ~40 to 3900 µg m-3. In the Large-scale and European kitchens, the time spent frying was identified as a determinant increasing personal exposure to total dust. The within-worker variance dominated the exposure variability of total dust in Large-scale and European kitchens, whereas between-worker variance dominated in Fast food and Asian kitchens. Exposure to total PAHs was statistically significantly higher for workers in the Asian kitchens. Also, exposure to NO2 was higher in the Asian kitchens, which all used gas stoves for cooking. The stationary measurements of total dust showed lower levels than personal exposures for most kitchens, whereas for PAHs, stationary levels were closer to personal exposure levels for all kitchen types. CONCLUSIONS: The results of this study increase the knowledge about exposure to air pollutants for kitchen workers of restaurant types that are common in Sweden and the rest of Europe. Personal sampling is essential for an accurate exposure assessment, and the large day-to-day variability in exposure levels points to the importance of repeated sampling.

Lung Cancer Among Firefighters: Smoking-Adjusted Risk Estimates in a Pooled Analysis of Case-Control Studies.

OBJECTIVES: The aim of this study was to explore lung cancer risk among firefighters, with adjustment for smoking. METHODS: We used pooled information from the SYNERGY project including 14 case-control studies conducted in Europe, Canada, New Zealand, and China, with lifetime work histories and smoking habits for 14,748 cases of lung cancer and 17,543 controls. We estimated odds ratios by unconditional logistic regression with adjustment for smoking and having ever been employed in a job known to present an excess risk of lung cancer. RESULTS: There was no increased lung cancer risk overall or by specific cell type among firefighters (n = 190), neither before nor after smoking adjustment. We observed no significant exposure-response relationship in terms of work duration. CONCLUSIONS: We found no evidence of an excess lung cancer risk related to occupational exposure as a firefighter.

Lung cancer risk among cooks when accounting for tobacco smoking: a pooled analysis of case-control studies from Europe, Canada, New Zealand, and China.

OBJECTIVES: To investigate the risk of lung cancer among cooks, while controlling for smoking habits. METHODS: We used data from the SYNERGY project including pooled information on lifetime work histories and smoking habits from 16 case-control studies conducted in Europe, Canada, New Zealand, and China. RESULTS: Before adjustment for smoking, we observed an increased risk of lung cancer in male cooks, but not in female cooks. After adjusting, there was no increased risk and no significant exposure-response relationship. Nevertheless, subgroup analyses highlighted some possible excess risks of squamous cell carcinoma and small cell carcinoma in female cooks. CONCLUSIONS: There is evidence that lung cancer risks among cooks may be confounded by smoking. After adjustment, cooks did not experience an increased risk of lung cancer overall. The subgroup analyses showing some excess risks among female cooks require cautious interpretation.

Myocardial infarction and occupational exposure to motor exhaust: a population-based case-control study in Sweden.

There is a well-established association between particulate urban air pollution and cardiovascular disease, but few studies have investigated the risk associated with occupational exposure to particles from motor exhaust. This study investigated the risk of myocardial infarction (MI) after occupational exposure to motor exhaust, using elemental carbon (EC) as a marker of exposure. A population-based case-control study of first-time non-lethal MI was conducted among Swedish citizens in ages 45-70 living in Stockholm County 1992-1994, including 1,643 cases and 2,235 controls. Working histories and data on potential confounders were collected by questionnaire and medical examination. The exposure to EC was assessed through a job-exposure matrix. Odds ratios (ORs) and corresponding 95% confidence intervals (CIs) were estimated by unconditional logistic regression. We investigated various exposure metrics: intensity, cumulative exposure and years since exposure. There was an exposure-response relation between the highest average exposure intensity during the work history and the risk of MI when adjusting for smoking and alcohol drinking (p for trend 0.034), with an OR of 1.30 (95% CI 0.99-1.71) in the highest tertile of exposure compared to the unexposed. An exposure-response pattern was observed in the analysis of years since exposure cessation among formerly exposed. Additional adjustments for markers of the metabolic syndrome reduced ORs and trends to non-significant levels, although this might be an over-adjustment since the metabolic syndrome may be part of the causal pathway. Occupational exposure to motor exhaust was associated with a moderately increased risk of MI.

Incidence of myocardial infarction among cooks and other restaurant workers in Sweden 1987-2005.

OBJECTIVES: The aim of this study was to investigate the incidence of myocardial infarction (MI) among cooks and other restaurant workers. METHODS: A prospective cohort study comprised manual workers in the service sector in the Swedish National Census of 1985, totaling 543 497 women and 233 999 men. Restaurant workers were identified by occupational codes. Information on first time MI during 1987-2005 was obtained from nation-wide registers. We used Cox proportional hazards modeling, with separate analyses for men and women, adjusting for age, hypertension, diabetes, and socioeconomic status. RESULTS: Female cooks, restaurant and kitchen assistants, and wait staff all showed a statistically significant increase in risk of MI [hazard ratio (HR) 1.34, 95% confidence interval (95% CI) 1.21-1.48; HR 1.12, 95% CI 1.03-1.21; and HR 1.25, 95% CI 1.06-1.47, respectively]. No increased risk was found among female cold-buffet managers. Among men, there was no statistically significant increase in risk for any of these occupations. The association was not stronger for subjects working ≥5 years. Group level information on smoking habits showed a similar percentage of daily smokers among female cooks compared to female manual workers in general. CONCLUSIONS: We found an increased risk of MI among female but not male cooks, restaurant and kitchen assistants, and wait staff. The excess risk may be related to occupational factors, but the results do not clearly support the hypothesis of cooking fumes as a risk factor for MI. Job strain could be a potential explanation for the findings.

No short-term respiratory effects among particle-exposed employees in the Stockholm subway.

OBJECTIVE: Exposure to traffic-related air pollution is associated with adverse respiratory effects, but it is not known whether the high exposure to particles prevailing in the subway system may affect the respiratory system. We investigated airway inflammation and lung function among particle-exposed subway employees. METHODS: We studied 81 workers. All participants were non-smokers, aged 25-50 years. Three exposure groups were formed according to particulate matter (PM) levels obtained during an occupational hygienic investigation: 30 platform workers [average PM(2.5) 63 µg/m(3) and DataRAM (MIE Inc, Billerica, Waltham, MA, USA) 182 µg/m(3)], 30 subway drivers (19 µg/m(3) and 33 µg/m(3)), and 21 ticket sellers (10 µg/m(3) and 13 µg/m(3)). We measured the fractional exhaled nitric oxide (FENO) of all workers before and after a workday. We also measured the peak expiratory flow (PEF) and forced expiratory volume in one second (FEV(1)) of platform workers and ticket sellers five times a day over two weeks. We calculated the arithmetic means of PEF and FEV(1) during exposed and unexposed time for every individual. RESULTS: There was no significant increase in FENO after work among platform workers, subway drivers or ticket sellers (the means of percentual individual change were -7%, +2% and -4% respectively). The averages of the ratios (exposed to unexposed time) of PEF and FEV(1) were above 1.0 for both ticket sellers (1.016 and 1.002 respectively) and platform workers (1.022 and 1.005). CONCLUSIONS: Our observations do not indicate any short-term respiratory effects of particle exposure in the subway among the employees, with respect to airway inflammation or lung function.

Incidence of lung cancer among subway drivers in Stockholm.

BACKGROUND: Very high levels of airborne particles have been detected in the subway system in Stockholm. Subway particles are more toxic to DNA in cultured human lung cells than particles from ambient air. METHODS: This cohort comprised all men in Stockholm County who were gainfully employed in 1970. They were followed for cancer incidence until 1989. Lung cancer cases were identified from the national cancer register. Subway drivers were identified from the census in 1970. The reference cohort comprised all transport and communication workers in Stockholm. RESULTS: There were nine cases of lung cancer among the subway drivers, giving a SIR of 0.82 (95% confidence interval 0.38-1.56). CONCLUSION: The lung cancer incidence was not increased among the subway drivers. The study gives some evidence against the hypothesis that subway particles would be more potent in inducing lung cancer than particles in ambient air.

Myocardial infarction in Swedish subway drivers.

OBJECTIVES: Particulate matter in urban air is associated with the risk of myocardial infarction in the general population. Very high levels of airborne particles have been detected in the subway system of Stockholm, as well as in several other large cities. This situation has caused concern for negative health effects among subway staff. The aim of this study was to investigate whether there is an increased incidence of myocardial infarction among subway drivers. METHODS: Data from a population-based case-control study of men aged 40-69 in Stockholm County in 1976-1996 were used. The study included all first events of myocardial infarction in registers of hospital discharges and deaths. The controls were selected randomly from the general population. National censuses were used for information on occupation. Altogether, 22 311 cases and 131 496 controls were included. Among these, 54 cases and 250 controls had worked as subway drivers. RESULTS: The relative risk of myocardial infarction among subway drivers was not increased. It was 0.92 [95% confidence interval (95% CI) 0.68-1.25] when the subway drivers were compared with other manual workers and 1.06 (95% CI 0.78-1.43) when the subway drivers were compared with all other gainfully employed men. Subgroup analyses indicated no influence on the risk of myocardial infarction from the duration of employment, latency time, or time since employment stopped. CONCLUSIONS: Subway drivers in Stockholm do not have a higher incidence of myocardial infarction than other employed persons.