New study: One week of night shifts per month does not increase the risk of coronary heart disease

If you clock in for work in the early hours when most of the population is still asleep, you may have heard that it increases the risk of heart disease. But now there is good news from Aarhus University for those of us who work night shifts. A new study shows no increased risk of coronary heart disease if you work up to seven night shifts per month. 

PhD Student Jesper Medom Vestergaard from the Department of Clinical Medicine is responsible for the study, which is based on working time registrations of more than 250,000 employees from 2007-2015, combined with their hospital records.

"In our study, we didn’t see  any association between the number of night shifts and the risk of coronary heart disease. Many international studies have otherwise suggested an association, which is why our results are interesting, not least because the previous studies are primarily based on questionnaires, whereas we’ve had an opportunity to compare specific data on working hours with people’s health information," says Jesper Medom Vestergaard.

In the study, Jesper Medom Vestergaard had access to day-to-day information on working hours for a total of 254,031 healthcare worers and other employees in the Danish regions, and this information was linked with their health information, including information from the Danish National Patient Register.

"Employees in the regions work on average 1.8 night shifts per month, and 93 per cent of them work fewer than seven monthly night shifts. The study shows that this is not associated with an increased risk of coronary heart disease."

Jesper Medom Vestergaard emphasises, however, that the results of the study do not mean that everyone working night shifts can breathe a sigh of relief.

"Most of the 250,000 paticipants in our study work in the healthcare sector, and few of them work nights permanently. Therefore, we can’t conclude that there is not an increased risk of  coronary heart disease associated with night shifts. Many other factors may be in play, but the data in the analyses were adjusted for age, sex, family history of cardiovascular disease and other diseases associated with coronary heart disease."

Jesper Medom Vestergaard will follow up with a new study, in which he will look at the risk of breast cancer, which has also previously been linked to night work.

The research results - more information 

• Type of study: The study is a register-based study based on a cohort of all 254,031 health care workers in Danish regions from 2007 to 2015, combined with health information, including information from the National Patient Register. 
• Partners: National Research Centre for the Working Environment, University of Copenhagen, Department of Public Health, University of California, School of Public Health, Berkeley, USA,
• Financing: The study has been financed by the Danish Working Environment Research Fund and Nordforsk.
• Information about deviations from the principle that the research results discussed in the press release must be based on a peer-reviewed article that has been published in an academic journal: The study has been peer-reviewed and published in the internationally recognised academic journal – International Journal of Epidemiology
• Read more in the scientific paper: https://academic.oup.com/ije/advance-article-abstract/doi/10.1093/ije/dyad126/7281366?utm_source=advanceaccess&utm_campaign=ije&utm_medium=email

Contact

PhD Student Jesper Medom Vestergaard
Department of Clinical Medicine, Health, Aarhus University
E-mail: jespvest@clin.au.dk

Clinical Professor and Chair Henrik Kolstad
Occupational Medicine, Department of Clinical Medicine, Health, Aarhus University
Mail: kolstad@clin.au.dk
Mobile: +4529610359