EBM and Clinical Support Librarians@UCHC

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Medical News, Public Health: Research on Shift Work, Circadian Disruption and Human Cancer Risk

In the news this past week have been research updates on the deleterious effects of night shift work upon human cancer risk. The International Agency for Research on Cancer (IARC), a part of the World Health Organization, conducts, coordinates, collects and disseminates information relating to carcinogenic substances, clinical causes of cancer and strategies for the control of this disease in humans throughout the world. It is the agency which publishes IARC Monographs on the Evaluation of Carcinogenic Risks to Humans.

A subsection of this series, “Overall Evaluations of Carcinogenicity to Humans: Group 2-A: Probably Carcinogenic to Humans“, was updated on Nov 29 2007. Read a press release from IARC announcing this update, which now lists Night-Shift Work as an environmental exposure assumed to be a “probable human carcinogen”. On the IARC website is also CancerMONDIAL which collects and publishes a periodical entitled “CI 5: Cancer Incidence on Five Continents”, free online at http://www-dep.iarc.fr/

The December 2007 issue of the journal Lancet Oncology (Volume 8, Issue 12) will feature an article detailing the latest research on circadian disruption, entitled “Carcinogenicity of Shift-Work, Painting and Fire-Fighting“.

London writer Maria Cheng wrote a news article entitled “Graveyard Shift Work Linked to Cancer” available on Wired.com (Nov 29 2007). However, the recent 2007 news reports are far from the first time the subject of circadian rhythm disruption, melatonin production, night-shift work and cancer risks have been reported by epidemiologists and cancer researchers.

As another brief example, following is a link to a 2001 news item from the Seattle Post-Intelligencer reporting on two surveys of American nurses published in 2001. The researchers found that the more nights, and more years, nurses worked during graveyard shifts, the higher their likelihood of developing breast cancer. In one group studied, the risk was estimated to be elevated by 60%. Read the news article here.

Dr. Richard G. Stevens, professor of community medicine at UConn Health Center, has been studying the effects of electronic light sources on human health for more than twenty years. He wrote in 1987 an article entitled “Electric Power Use and Breast Cancer: A Hypothesis“, published in American Journal of Epidemiology, Vol. 125, Issue 4 (1987). Here is a screenshot of a few of his recent citations, found on PubMed:


Dr. Stevens was one of three epidemiologists who were recently interviewed on the National Public Radio series, Where We Live which was broadcast on WNPR (Connecticut National Public Radio station) on Nov 30 2007.

Other scientists featured on this program were IARC epidemiologist Dr. Vincent Cogliano (a co-author of the Lancet Oncology article cited above) and Dr. Mark Rea, Director of the Lighting Research Center at Rensselaer Polytechnic Institute. Their interviews are available as a podcast (screenshot follows):


Image and Podcast courtesy of National Public Radio and WNPR – Copyright 2007 – All rights reserved.


One response to “Medical News, Public Health: Research on Shift Work, Circadian Disruption and Human Cancer Risk

  1. Ed Coburn January 5, 2008 at 8:51 PM

    And let’s not forget that the IARC found a correlation between shiftwork and cancer, not a causal relationship. Further research is needed to better understand what it is about shiftwork and the behavior of shiftworkers that is behind this slightly elevated cancer risk.

    The IARC announcement is what it is — nothing more, nothing less. It’s important but does not identify a specific solution, and even if it did, we can’t stop the 24/7 society. We are hooked on public safety, national security, electrical power, transportation, retailers, and all sort of other services that we expect to be available 24 hours a day.

    So, as always, shiftworkers and their employers should take all reasonable measures, based on the best available scientific evidence, to optimize alertness, health and safety.

    Ed Coburn
    Executive Director
    National Shiftwork Information Center

    P.S. I discuss this IARC announcement on my blog post at http://shiftworkinformation.blogspot.com/2008/01/night-shift-work-raises-cancer-risks.html.

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