Cancer risk among nurses

The working environment of nurses contains both known and suspected influences that may lead to an increased risk of cancer, such as shift work, radiation, sterilization gases, risk of infection and night work. This project investigates these relationships in more detail.
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In collaboration with the National Institute of Occupational Health, the Cancer Registry of Norway has conducted research on cancer risk among nurses for many years.

The project started as early as 2000, when we collected information (date of birth, education, place of work) on almost 45,000 Norwegian nurses who were trained in the period 1914-1984.

The reason for our interest was that international research had shown an increased risk of breast cancer in many studies of nurses in other countries. It was also known that the working environment and working conditions of this group contained both known and suspected influences that could lead to an increased risk of cancer, such as ionising radiation, sterilising gases, risk of infection and night work.

Data basis

What is registered about each individual is, firstly, the answers from the interview that was conducted in 2009.

For the nurses who had breast cancer, data on the disease have been registered, based on linkage with information from the Cancer Registry.

The third type of data recorded about participants is genetic information from the saliva samples that were submitted.

All analyses are based on anonymised data.

All participants may withdraw from the project at any time without giving a reason by contacting the National Institute of Occupational Health.


In the first follow-up study we conducted, we found that the overall cancer risk for the period 1953-2002 was on a par with the general population.

However, the risk of cancer, particularly related to tobacco, alcohol and HPV infection, was significantly lower among nurses, while the risk of breast cancer, ovarian cancer and malignant melanoma increased by 14-15 per cent.

For breast cancer, the risk was more than doubled for those who had worked night shifts for 30 years or more, compared with those who had not worked night work after their studies.

We found no evidence that ionising radiation affected the risk of cancer.

In the next phase of the project, we conducted interviews with nurses who had breast cancer and a control group without the disease, and collected detailed data on various influences in their work and shift work in particular. Analysis of these data showed, among other things, that working in shift schedules with many consecutive night shifts over several years increases the risk of breast cancer among female nurses.

Furthermore, we have found that the association between night work and breast cancer risk may vary somewhat for different types of breast cancer. Since night work involves changes in the normal circadian rhythm, research in this field in recent years has also involved studies of variations in so-called clock or circadian rhythm genes, and in receptors for the hormone melatonin and for female steroids.

Analyses of saliva samples from the participants showed, among other things, that special gene variants can modify the risk of breast cancer. These analyses were conducted at group level to understand mechanisms, and not to calculate individual risk.

Examples of media coverage of the project:

Many night shifts increase the risk of cancer (Aftenposten, 03.04.2011)
Many nights - more breast cancer (Sykepleien, 14.04.2011)
Doubled cancer risk with long-term shift work (, 02.07.2013)

See the bottom of this page for an overview of published research articles from the project.


There are still several interesting and important issues that we want to study, based on collected data and biological material. In addition, we wish to compare the relationship between night work and breast cancer risk among nurses in Norway with the risk in other countries, using similar exposure variables and analysis methods for gene variants as in the Norwegian studies.

The original licence to process personal data from this project now expires. We must therefore obtain new written consents from the participants in order to continue.

Therefore, the National Institute of Occupational Health is now addressing all the nurses who were interviewed in the spring of 2009 in connection with the project. We are very grateful to everyone who participated in the important project, and hope for a positive response so that we can analyze your data until 31.12.2022. 

Participant information

See here for information for the participants in the study.


1. Jenny-Anne S. Lie, PhD, Helge Kjuus, MD, PhD, Aage Haugen, PhD, Shanbeh Zienolddiny, PhD, Richard G. Stevens, PhD, Kristina Kjærheim, MD, PhD:
Night work and breast cancer risk among Norwegian nurses: Assessment by different exposure metrics.
American Journal of Epidemiology 2011;173(11):1272-1279.

2. Jenny-Anne S. Lie, Helge Kjuus, Shanbeh Zienolddiny, Aage Haugen, and Kristina Kjærheim:  
Breast Cancer Among Nurses: Is the Intensity of Night Work Related to Hormone Receptor Status?
Am. J. Epidemiol. 2013 178: 110-117

3. Shanbeh Zienolddiny, Aage Haugen, Jenny-Anne S. Lie, Helge Kjuus, Kristina Haugen Anmarkrud and Kristina Kjærheim:    
Analysis of polymorphisms in the circadian-related genes and breast cancer risk in Norwegian nurses working night shifts.
Breast Cancer Research 2013, 15(4):R53

4. Johanna Samulin Erdem, Øivind Skare, Marte Petersen-Øverleir, Heidi Ødegaard Notø, Jenny-Anne S. Lie, Edyta Reszka, Beata Pepłońska and Shanbeh Zienolddiny: Mechanisms of Breast Cancer in Shift Workers: DNA Methylation in Five Core Circadian Genes in Nurses Working Night Shifts.    
Journal of Cancer. 2017; 8(15): 2876-2884.

5. Samulin Erdem J, Notø HØ, Skare Ø, Lie JS, Petersen-Øverleir M, Reszka E, Pepłońska B, Zienolddiny S:
Mechanisms of breast cancer risk in shift workers: association of telomere shortening with the duration and intensity of night work.
Cancer Med. 2017 Aug;6(8):1988-1997. doi: 10.1002/cam4.1135. Epub 2017 Jul 14.