Occupational epidemiology and chemical exposure assessment

The research is focused on occupational epidemiology and exposure assessment methods. Focus has long been on occupational chemical exposures, cancer and cardiovascular diseases but recently we have added exposure to noise and effect on the phoetus to our research program. Examples of findings include quantification of the smoking-adjusted risk of lung cancer and myocardial infarction after occupational exposure to motor exhaust and particles. We have improved exposure assessment methods and have developed and applied Job Exposure Matrices (JEMs) for a large number of occupational exposure factors.


Occupational air pollution during pregnancy and health effects in children

A majority of women in child bearing ages in the industrialized part of the world are employed today. This high prevalence of employment leads to a high number of pregnancies with potential exposure to various occupational hazards. In 2009, 23% of employed women in the age of 16-29 and 16% of employed women in the age of 30-49 in Sweden reported exposure to occupational air pollution during at least ¼ of the working-day. This corresponds to a significant number of exposed pregnancies.

Air pollution in the residential area has in previous studies been associated with low birth weight, pre term birth and small for gestational age. Many employed women have similar exposure to traffic generated air pollution in their working environment, but in higher levels. In addition, employed women can also be exposed to other kinds of air pollution in their work. No previous study has assessed the risk of health effects such as low birth weight in the offspring in relation to exposure to occupational air pollution during pregnancy. The aim of this study was to observe if occupational air pollution at work are related to birth effects, such as low birth weight, small for gestational age and preterm birth.

The study is a nationwide study including all births in Sweden between 1986 and 2008. This cohort of children will be formed through a merge of information from three different population based registers. Information on occupation during pregnancy will be gathered from the Medical Birth Registry at the Swedish National Board of Health and Welfare together with background characteristics such as maternal BMI, smoking habits, parity and ethnicity. Information on education, income and days of unemployment will be collected from The LISA-register at Statistic Sweden. Information on long-term leave of absence, such as sick-leave and parental leave will be gathered from the Social Insurance registry at the Swedish Social Insurance Agency.

Occupational air pollution will be assessed through a job-exposure-matrix. This matrix is constructed of measurements and assesses the air pollution exposure for 20 different types of particles during 4 different time-periods within 300 different occupations.

Information on air pollution exposure at the residence at the time of pregnancy will be calculated at SMHI by the use of the national model-system SIMAIR. Air pollution levels will be calculated at each coordinate of address the participant have had during pregnancy. The data will then be used for confounding control and interaction analysis.The study is financed by the Swedish Research Council for Health, Working life and Welfare (FORTE) and the study will help to retrieve valuable knowledge on the effects of the mothers exposure to air pollution on the fetus that will be useful in future guidelines for occupational air pollution exposure during pregnancy.

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Jenny Selander

Principal Researcher

Occupational exposure to chemicals and breast cancer

Cancer of the breast is the most common cancer in women and the leading cancer related cause-of-death among women in Sweden. The risk depends strongly on hormonal factors. Exposure to ionizing irradiation and shift work increase the risk. The influence from occupational exposure to chemicals is less well investigated. A few studies indicate that organic solvents may increase the risk, and an elevated risk has been observed among laboratory technicians in chemical labs and among hairdressers/cosmetologists. Few of these studies were adjusted for potential confounders, and the conclusions are limited. It is urgent to investigate the association between chemical occupational exposures and breast cancer with adjustment for potential confounders like pregnancies and hormone medication. This study investigates the risk of developing breast cancer after occupational exposure to chemicals, using two data sets:

I: The Malmö diet and cancer-study holds information on occupation and a number of personal factors related to the breast cancer risk for over 17 000 women. The occupational exposure to various organic solvents is investigated by a Job Exposure Matrix, supplemented by individual exposure assessments by an occupational hygienist. The risk of breast cancer associated with exposure to organic solvents and in various occupations is estimated by case-control technique, including all around 1 000 cases of breast cancer and around 2 000 controls, adjusting for potential confounders. We also investigate if hormone receptor status of the tumours modifies the risk of chemically induced breast cancer.

II. We update a cohort of 2 247 female laboratory technicians employed at the Karolinska Institutet and Karolinska University Hospital. A previous follow-up showed an elevated risk of breast cancer among women who had worked for more than 10 years in chemical laboratories.

The findings are of importance for prevention of excess cases of this common form of cancer among women.

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Occupational exposure to particles and cardiovascular disease

In Sweden and the rest of the world, cardiovascular disease is one of the leading causes of death. When we inhale particles from air pollutants the risk for heart disease increases. In Sweden it is estimated that more than 5000 people per year die prematurely due to air pollution. Many are exposed to much higher levels of air pollution on their jobs, such as chimney sweeps, construction workers, welders and miners, and in these occupations are also more likely to suffer a heart attack. It looks as if higher levels of air pollution, both in outdoor air and at work, increase the risk of heart attack. But air pollution consists of particles of different sizes and a variety of chemical substances, and we know very little about the ingredients in this blend and how it affects the risk of heart attack.

In a previous study, with support from FAS, we have found that people who work in occupations where there is a lot of particles in air pollution, such as in industrial environments, have higher risk of heart attack than those who have jobs with a clean environment. We have also seen that heart attacks are more common among those who had air polluted work for an extended period, and women seem to be more sensitive than men. In occupations with a lot of combustion particles, for example from engines, there were more heart attacks than in occupations where particles are formed by processing material such as wood and metal. The main difference between these two types of particles is the size. Combustion particles are extremely small and affect the body's biological processes in a different way than particles of larger size.

In the next study we want to look at women in air polluted occupations and try to find what it is in the air that are related to their increased risk of myocardial infarction. Is it the size of the particles, or rather what they consist of that is important? If we can protect us against dangerous air pollution the risk of heart attack can be reduced.

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Pernilla Wiebert

Affiliated to Research

Foetal noise exposure during pregnancy and health effects in the children – FENIX

Noise exposure is still common in occupational settings even though health effects from occupational noise exposure, such as hearing loss, have been established a long time ago. Hearing protection devices are the most common precautionary action against occupational noise exposure, but this measure does not protect the foetus during pregnancy. Low frequency noise (<250Hz) is not reduced during passage of the abdominal wall and the amniotic fluid, and higher frequencies are only partially reduced.

This project investigates if maternal exposure to noise during pregnancy causes hearing dysfunction or reduced birth weight in the children. The study includes over 1.4 million births in Sweden 1986-2008. Information on maternal exposure to noise during pregnancy is derived from a job exposure matrix. Information on sensorineural hearing loss and tinnitus is obtained from the patient registry. Length of gestation and a number of potential confounders is obtained from the national medical birth registry. Data on sick leave and pregnancy benefits are obtained from the Swedish Social Insurance Agency.

There was an excess of hearing problems among children whose mothers had worked full-time in jobs that were high exposed to noise ( > 85 dBA) during pregnancy, hazard ratio 1.82 (1.08-3.09). The risk of the child being small for gestational age (SGA) increased with exposure to noise; hazard ratio was 1.16 (1.08-1.25) among mothers working full-time and exposed to 75-85 dBA and 1.44 (1.03-2.02) among those exposed to >85 dBA compared to those exposed to < 75 dBA.

This study supports that high exposure to noise during pregnancy should be avoided.

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Mesoamerican nephropathy – a devastating epidemic

Chronic Kidney Disease, CKD, is increasing in both developed and developing countries, greatly expanding the need for chronic dialysis and renal transplantation. A widespread epidemic of CKD of uncertain etiology has been detected in Central America and Mexico and been named Mesoamerican nephropathy, MeN. The epidemic occurs mainly among sugar cane cutters, working under extremely hot conditions, and in lesser extent also among workers in several other hot occupations. Reports of a similar kind have been published from Sri Lanka and Thailand. A wide variety of etiologies have been proposed, including exposure to herbicides, pesticides, heavy metals, toxins , drugs (NSAIDs), infections, metabolic causes, and the effects of heat stress and recurrent dehydration. A multifactorial etiology is likely with long-term occupational heat stress and recurrent dehydration as a necessary factor. IMM researchers have studied the epidemic for 10 years and are involved in several epidemiologic projects that aim to identify the causes of MeN and to evaluate work place interventions against dehydration and heat stress in a broad international collaboration. We are also leaders of CENCAM (Consortium on the Epidemic of Nephropathy in Central America and Mexico) where many North and South American as well as European researchers are members.

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Working hours and health

Background: Shift work and especially night work disrupts the circadian rhythm, leading to hormonal changes including the diurnal melatonin cycle. About 16% of Swedish employees regularly work at night and 22% work on shift. The proportion of shift- or night-workers is especially high in the health care sector, where about 50% of the employees work at night or on shift. Shift or night work causes sleep deprivation and is linked to an excess of cancer, pregnancy complications as well as cardiovascular disease. Previous studies have indicated an excess of breast cancer in women working shift or night. It is a common question whether pregnant women can or should work at night, considering reports of miscarriage, premature birth or reduced birthweight in the children.

Relevance: There is ample evidence for negative health effects from shift or night-work, but data on working hours is self reported, less precise, and collected in retrospect after the cases have appeared. Large studies with detailed and objectively collected data on working hours are needed as a basis for practical advice on how shift schedules should be planned in order to reduce negative health effects.

Material and methods: Stockholm County Council employs a large number of health care workers working on shift or at night. The computerized register of employees holds very detailed individual records on working hours for around 35 000women and 9 000 men employed from 2009 and onwards. Information on outcomes and confounding factors are obtained from national registers: the cancer registry; medical birth registry (pregnancy outcome, number of children, age at first child, smoking habits, length and height, etc.); pharmacology drug register (use of hormone replacement therapy).

Analysis: The risk of cancer and pregnancy outcome is estimated among those working various types of shift or at night, using daytime workers as a control group, while adjusting for potential confounders.

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A sustainable new working life – trends, health effects and governance

The structures of the Swedish labour markets are rapidly changing, and challenge current systems to ensure sustainable working conditions. These changes are not monitored sufficiently through current information systems based on surveys and workers’ compensation claims.

The aims of the programme are to

  1. Assess trends in working conditions throughout the labour market, overall and with stratification to cover heterogeneity associated with e.g. age, gender, and ethnicity
  2. Explore the health impact of working conditions in a life-course perspective, taking the full complexity of multiple exposures into account
  3. Systematically explore the impact of different approaches to governance, from the changes in the institutional framework to soft-law and knowledge alliances.

The proposed programme will establish a comprehensive set of job-exposure matrices (JEM) on various occupational exposures and employment conditions, gender balance and training opportunities linked to data on occupational titles, company size and industry. These data will be matched to a data base including the entire population in Sweden in the LISA-register from 1990 and onwards, and outcomes (health, work participation etc.) from national registers. A series of longitudinal epidemiological studies will be performed of determinants for entry, exit (and re-entry) into work, as well as health-impact assessments of various work environment factors. Finally, the efficiency of different approaches to governance of the work environment will be systematically explored in a series of studies performed in close collaboration with major stakeholders on a local and national level (e.g. social partners, schools, municipalities, and national governing bodies).

The programme is financed by FORTE and is performed by a multidisciplinary team of researchers, involving experts in occupational epidemiology, social epidemiology, law, labour economics, work organization, exposure science, biostatistics, and computer science.

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Maria Albin

Content reviewer:
Anna Persson