O4E.3 Utility of routinely recorded data on working hours for an epidemiological cohort study of 60,000 swedish health care employees

Night and shift work is common in industry and service that must be functional 24 hour. Night work disrupts the circadian rhythm, and is potentially linked to an excess of cancer (especially breast cancer), cardiovascular disease, pregnancy complications, as well as to psychical effects. Large studies with detailed and objectively collected data on working hours are needed to confirm causal associations and develop practical advice on how shift schedules should be planned in order to minimize negative health effects.Stockholm County Council employs a high number of health care workers of which many are working in shifts. We have formed a cohort of those employed from 2008 to 2016, 45 000 women and 15 000 men. The computerized employment register holds individual records on working hours day by day in retrospect since 2008, and information on night work since year 2000. Information on cancer incidence, hospital discharge diagnoses of cardiovascular disease, pregnancy outcome, and causes of sick-leave have been obtained from national central registers.There were typically three work shifts: morning shifts (07–15), afternoon shifts (14–21), and night shifts (21–07). Non shift-workers typically worked (08–17). So far, we have investigated work shift patterns for those with a high percentage of night work: nurses, assistant nurses and midwives. Among these, 22% worked at least one night per month, and 15% worked at least 5 nights per month in 2009, which increased slightly to 23% and 16% respectively in 2016. It was common to work several nights in a row: in 2009 13.8% worked at least 3 consecutive nights or more per month, which increased to 15.5% in 2016. Only 0.6% worked 5 consecutive nights or more per month.Analyses of cancer, pregnancy outcome, cardiovascular disease and psychical outcomes are planned for 2019.