Working hours and health

Shift work and especially night work disrupts the circadian rhythm, leading to hormonal changes involving the diurnal melatonin cycle. Around 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, in which about 50% of the employees work at night or on shift. Shift or night work causes sleep deprivation and is with a varying degree of certainty linked to an excess risk of cancer, pregnancy complications, cardiovascular disease as well as to psychical symptoms like depression. Some previous studies have indicated an excess risk of breast cancer in women working shift or at night. It is a common question whether pregnant women can or should work at night, considering reports of an increased risk of premature birth or reduced birthweight in the children.

There is ample indicative evidence for negative health effects from shift or night-work, but many earlier studies lack precise data on working hours. 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.

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 45 000 women and 15 000 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.); in-patient register (cardiovascular diseases), national insurance agency (sick-leave diagnoses), and pharmacology drug register (use of hormone replacement therapy).

The risk of cancer, cardiovascular disease, pregnancy outcome, and psychical diagnoses is estimated among those working various types of shifts or at night, using daytime workers as a control group, while adjusting for potential confounders.

A parallel study applies qualitative method to investigate factors related to healthcare professionals’ perception of night work and intention to leave the workplace/profession. Around 35 individual interviews with nurses and midwives will be performed and analysed.

Contact persons

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Carolina Bigert

Adjunct Lecturer
Content reviewer:
Anna Persson