Night Shift S**t

In the last month or so, I keep coming across articles related to the study released last month suggesting that nurses who work the night s**t, I mean shift have a higher potential for developing FBC. Why the slip of the tongue, you ask?  Well as if working the night s**t (oops! I did it again) isn’t hard enough. I mean, really.

This study has had a significant impact on me because my first job out of nursing school was working the night s**t (ok, I need to rename it…or else I’m going to have to wash out my own mouth!) in an Intensive Care Unit. The hours were awwwwwwful!

I was delirious most of the time and am quite honestly still a little traumatized by it. Being up all night on steroids during chemo frequently reminded me of this wretched period of time. The 4:00 am – 6:00 am period was the worst part of the shift. I found myself doing jumping jacks and other calisthenics to keep myself awake. NO amount of Diet Mountain Dew (YES, that IS what I drank at the time. I admit it!) could keep me up.

I would say that 3/4 of the nursing staff was new to the profession and working this s.h.i.f.t. (there, I said it without swearing!) to do time in order to move to the day shift. The other 1/4 of the people braving the long nights were career “night nurses.” They worked full-time nights because either they had to (because of family obligations) or because they didn’t like people. Really. Because you KNOW that I asked WTF they intentionally subjected themselves to the sheer misery. I felt sorry for the women (for some reason, I only worked with women on nights) who had to do it and was pretty frightened of the others (I vividly remember one woman who said that she was going to do everything that she could to wipe the smile off of my face. Seriously.).

Anyway, back to the topic at hand.

The Study

The Nested case-control study of night shift work and breast cancer risk among women in the Danish military is the study in the journal Occupational and Environmental Medicine conducted by lead researcher Johnni Hansen, of the Institute of Cancer Epidemiology at the Danish Cancer Society, in Copenhagen (phew, that was a mouthful, but I wanted to give you the full resource!).

Hansen and his colleagues studied 18,500 women who were in the Danish Army between 1964 and 1999. The researchers followed-up with 141 women who had developed breast cancer by 2005-06, and compared their medical histories with those of 551 women in the military who did not develop the disease. All of the participants filled out a detailed 28-page questionnaire asking about their working habits and whether they considered themselves “morning” or “night” people.

The researchers also asked the women about other factors that could affect breast cancer risk, including whether they used contraceptives, how many children they had, whether they used hormone replacement therapy if they were past menopause, and if they sunbathed.

What does the study say?

After taking into account the other factors that could influence a breast cancer diagnosis (contraceptive use, number of children, sunbathing, and use of hormone replacement therapy), the researchers found that:

  1. Women who worked night shifts had a 40% higher risk of developing breast cancer.
  2. Women who worked 3 night shifts each week for at least 6 years or more had double the risk of developing breast cancer compared to respondents who did not work at night.
  3. Women who categorized themselves as “morning people” and worked night shifts were at an even higher risk of developing breast cancer—4 times the risk of the participants who did not work night shifts.

Geesh!  These are really alarming findings, right?!?

What is the link to cancer?

Hansen suggests that the night shift work involves exposure to light that disrupts the body’s circadian rhythm. This affects levels of melatonin, a hormone that is believed to have healing, antioxidant (i.e., anti-cancer) properties. Melatonin levels normally increase during the darkness of night, but the artificial light of a night shift suppresses them.

Hansen also theorized that disturbances to a person’s circadian rhythms, a natural result of working nights, may have a role in the development of cancer. “Repeated phase shifting may lead to defects in the regulation of the circadian cell cycle, thus favoring uncontrolled cell growth,” Hansen said. He also suggested that the stress of working nights may cause suboptimal performance of a person’s immune system, which can result increased growth of cancer cells.

Additionally, because night workers labor (an understatement!) under artificial light, they may be exposed to less natural sunlight and, therefore, less vitamin D from the sun’s rays than day workers and lower levels of vitamin D have been linked to increased risk of breast cancer.

What is the Silver Lining ?

The study suggests that if women work fewer night shifts, the risk of cancer subsides. Women who worked only one or two night shifts a week showed no increased risk of cancer. “Since night shift work is unavoidable in modern societies, this type of work should be limited in duration and limited to less than three night shifts per week,” Hansen said.

FYI (in case you didn’t know it), typical nursing night shifts consist of 3, 12-hour shifts from 7:00 pm – 7:30 am and/or a combination of 2, 12-hour shifts from 7:00 pm – 7:30 am and 2, 8-hour shifts, from 11:00 pm – 7:30 am. Yes, it is indeed as grueling as it sounds.

How accurate is this study?

When I was a student in bioethics at the University of Chicago, one of the things that we learned to do was to read clinical studies critically.  In other words, it is important to look at everything that goes into a study to figure out how accurate results are.  You’d be surprised by how inaccurate some study results actually are. Even the fancy studies.

In case-controlled studies (which is what this study is), they typically can’t tell us if one thing causes another. In other words, we can’t be sure from this study that working night shifts causes women to have breast cancer.

Additionally, using questionnaires to ask people about their habits is not the best way to collect reliable information. People may not recall information accurately, and this can make the results less reliable. Also, many of the women dropped out of the study over the years, either because they died, or the researchers couldn’t contact them or they didn’t want to take part. Overall 1 woman in 3 who started the study was not included at the end. This could also have made the study less reliable.

So, in terms of this study, right now, the reasons for these findings are uncertain. Third-party scientists say that more work is needed to definitively establish a link between breast cancer and night shifts.

What does this study mean for me/us? 

We don’t know how much working night shifts raises a woman’s risk of breast cancer in absolute terms. It may be that the increased risk is caused by other factors that were not accounted for in this study. We still need more evidence to be sure that this link is genuine.

So, there you have it.  I think that it has been a super popular topic because the media could spin it – very effectively, I might add. While the results of this study are certainly intriguing, more research is needed to shed more light on the relationship between shift work and developing cancer. In the meantime, people who are required to work nights can help reduce their risk of breast cancer by limiting alcohol consumption, increasing exercise and controlling weight, all things that are within our control (Silver Lining).


Hansen J, Lassen CF. Nested case-control study of night shift work and breast cancer risk among women in the Danish military. Occupational and Environmental Medicine. Published online 29 May 2012.


Leave a comment


  1. says

    I think a lot can happen in the body due to lack of the proper schedule of sleep. Not just working the night shift, but having insomnia can lead to health issues. I suffer from insomnia and have fibromyaliga and other autoimmune diseases. The insomnia started ten years ago. I have had breast cancer twice since then. I think, then, the idea the WORLD should take from this is stop having newbies be the only ones who work night shifts. Everyone should work it just one or two days a week so that we are not putting all the nurses, and all the patients, at any kind of lack of quality of life or care. My mother was a flight attendant for years who flew internationally out on red eyes to Japan, New Zealand, etc. Her arthritis and other problems started from then. A lot of night shift type jobs are just so exhausting and disruptive to the bodies immune system. However, we unfortunately need people for certain jobs at night so why not plan it better? Also, as I write in my blog, be aware of blame games. There is no one reason we get cancer. There is nobody to blame, especially ourselves. This only causes stress. Take these studies to heart but not so much you blame your own situation. Just allow it to be part of your presence and awareness of a more enlightened world to hopefully come.

    • says

      Dear Miki,
      I couldn't agree more about NOT blaming! Stress is the LAST thing anyone needs. Right on! Your note is so beautifully written. Thanks so much for sharing!
      Best wishes to you.
      Thank you, again!

  2. Kim C says

    One more thing….. Have you heard about the link to conventional cotton clothing and breast cancer? To the effect that organic cotton is a healthier product and is processed with less chemicals.

  3. Kim C says

    When I was in hospital, one of my (fave) nurses told me she was thinking about leaving the shift work on the wards (4×12 hour shifts and 4 days off) because studies showed that this pattern over an extended period of time (not sure how long) can take years (10) off ones life. I saw her about a year later and she had found a great nursing position in public health, working regular hours. Good for her!!! Good for you for putting this information out there…..!