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Special Report

Special Report: Is Shift Work Killing You?

Scheck, Anne

doi: 10.1097/01.EEM.0000440683.90775.03

    Once there was an experienced emergency physician — skilled, highly regarded, much-published — whose concentration waned during the wee hours of an overnight shift. By the time dawn rolled around, this doctor simply wasn't as sharply engaged with residents.

    Nobody but Rita Cydulka, MD, who worked in this emergency department, seemed to notice it so she decided to tell her colleagues. She had pretty good evidence on hand to make her point — the focus-losing physician was Dr. Cydulka herself. “I just wasn't hearing all that was being said at that hour in the morning, and I was well aware of that,” she recalled.

    Dr. Cydulka, a professor and the vice chair of emergency medicine at Case Western Reserve University in Cleveland, proposed a solution: Stop making night shifts a mandatory part of the schedule for those 50 and older.

    It took some campaigning, but now physicians over that half-century mark who have practiced with the group for at least 10 years are no longer required to work nights in the ED. The change, instituted about five years ago, translated into higher retention rates for older emergency physicians and encouraged younger ones to stay on as well. As Dr. Cydulka puts it, they know the day will come when they will qualify for the same schedule.

    “At one point, we actually got a little concerned that nobody would want to leave,” said Dr. Cydulka, who is also the medical director of quality process at MetroHealth Medical Center.

    Having passed that age-milestone herself, Dr. Cydulka seems way ahead of her time, and not just because she wanted to stop night shifts to help keep team members at their best. Recent studies suggest this kind of move may do even more than that. It may help protect against the risk of serious illness, even chronic disease.

    Two studies have shown that what is being called a “probable carcinogenic effect” is related to late-night or overnight shift work. One looked at prostate test results, the other at breast cancer. (J Natl Cancer Inst 2013;105[17]:1292; Occup Environ Med 2013 Jul 1[Epub ahead of print].) A third noted a range of health consequences such as increased risk for diabetes, cardiovascular disease, and cancer, and suggested light may be a countermeasure to minimize circadian disruption while maintaining alertness. (J Perinatol 2013;33[Suppl 1]:S17.) All three studies included large samples via databases or meta-analysis.

    A review of more than 30 studies to determine the possibility of a correlation between shift work and vascular events showed a strong association with increased risk of coronary events, notably myocardial infarction and ischemic stroke. (BMJ 2012;345:e4800.) So many different kinds of studies were within this review, however, that definite conclusions couldn't be drawn about the underlying reasons that shift work seems to confer such a substantial risk.

    The prostate study, which utilized data from the National Health and Nutrition Examination Survey (NHANES), showed elevated prostate-specific antigen (PSA) levels in men who performed shift work. The NHANES results appear to indicate that sleep disruption and interference with circadian rhythm is associated with elevated PSA levels, a marker for an increased risk of developing prostate cancer.

    The breast cancer study compared 134 breast cancer cases with 1,179 cases from a control group matched for age and other factors in Canadian women. The study — one of the very few on shift work in the general population — demonstrated an association between 30 or more years of shift work and breast cancer, with no interaction by tumor hormone-receptor status.

    So does long-term shift work actually predispose some women to cancer? It appears, at least, to be related to the presence of the disease in some of them, but the differences are unlikely to be simply a function of age, said Anne Grundy, PhD, the lead author of the study.

    “I think it's likely the effects of duration of shift work that are seen are likely due to some other factor that has an effect over time ... for example, perhaps sustained disruption of circadian rhythms,” explained Dr. Grundy, a postdoctoral fellow at Cancer Care Ontario.

    If duration of night-shift work is one of the characteristics in the etiology of this probable carcinogenic effect, then stopping it at age 50 may be a way to reduce risk. But that's theoretical, said Dr. Grundy.

    “I think what we've been suggesting, based on the results of our study, has been potentially simply trying to limit the number of years of shift work that individuals work, as opposed to a strict age cutoff,” she said. “However, for people who've spent their entire working life in shift work, obviously having an age-cutoff would accomplish the same thing.”

    It is next to impossible to determine from the medical literature which night-shift patterns are linked to the highest health risk. With the exception of one Norwegian study two years ago that suggested that six or seven consecutive night shifts are associated with the most significant impact, investigations to date haven't assessed differences in night scheduling with much precision. (Am J Epidemiol 2011;173[11]:1272.)

    “All the shifts have been lumped together a lot into one big box,” Dr. Grundy said. “I think a better way to reflect the current state of research would be to say that more recent studies are beginning to focus on the effects of additional shift work characteristics — shift type, shift pattern— and that the Norwegian study is a good example of this.”

    Nearly a decade ago, French researchers showed that long-term exposure to night-shift work is linked to cognitive decline. They had fairly compelling data: 3,000 people in age groups that ranged from ages 32 to 62 at 10-year intervals. (Ergonomics 2005;48[10]:1282.) Yet the study also suggested that the brain is fairly flexible; deficits in cognitive function were reversible after a rest period.

    Almost anyone who has stayed up all night knows that sleep is restorative, but this investigation showed sleep can reset the brain even after repeated disruptions. “We want everyone to be well rested when they show up for their shift,” Dr. Cydulka said. The switch at her group wasn't made simply to keep a mix of younger and older physicians — a good combination for the medical center's residents — it was also done with an eye on patient safety. Is there resentment among younger members of the team? It's likely, she acknowledged when describing the no-nights perk, but physicians who work these time slots usually accumulate more pay because of the higher relative-value units associated with night shifts. “I think this helps [offset] that,” she said.

    Some shift workers seem relatively unaffected by the schedule, and show little evidence of differences in physiology. “I think [some] shift workers have some genetic component that allows them to adapt to this, but some never do,” said Mariana Figueiro, PhD, who led the study reviewing health consequences. Staging light cycles to keep the biologic clock on its regular circadian rhythm might be a way of mitigating this, said Dr. Figueiro, an associate professor at Rensselaer Polytechnic Institute in Troy, NY.

    Certain forms of lighting at specific wavelengths have been shown to affect alertness in rotating shift workers. Light exposure also can initiate phase-shifting of the human biological clock. Yet prevention is an approach that has yet to be fully explored. “There is good evidence from laboratory studies [in sleep labs] that exposing people to bright light during the night reduces overnight melatonin production,” Dr. Figueiro said.

    It may be that brief napping, perhaps as well as lighting changes, could confer some protection. Certain dietary supplements may prove beneficial as well. “No other studies have looked at these countermeasures and how they might affect the health and well-being of shift workers. We probably need more of them,” she added.

    Melatonin, for example, has been suggested as playing a role in cancer vulnerability in shift workers. Melatonin levels, however, were relatively unchanged among nurses whose work week was two 12-hour night shifts along with two 12-hour days, then no work shifts for five days in a row, Dr. Grundy noted. Results from observational studies have been more mixed with respect to the impact of night shifts on melatonin levels.

    Data from the Nurses' Health Study cohort in the United States has shown that having worked at night during the previous two weeks was associated with decreased melatonin,” Dr. Grundy said. “But long-term history of shift work was not, which was what we found in our study of the rotating-shift nurses. I would be more inclined to describe the impact of night-shift work on melatonin as a hypothesis rather than an established relationship.”

    The data so far appear to support the concept that shift work may aggravate or exacerbate susceptibility to disease, but by what mechanism? Investigators know, for example, that Swedish shift workers have a lifetime risk of developing peptic ulcer disease that significantly exceeds that of other employees but not why. (Scand J Work Environ Health 2010;36[2]:85.) Nearly 50 percent of the population has Helicobacter pylori, the bacterium implicated in peptic ulcer disease, and it would appear that shift work somehow triggers the infection to become the digestive disease.

    “It is likely that many other factors and biomarkers may play a role” in the proposed link between night shifts and health risk, Dr. Figueiro said. Shift workers are disrupted, so their overall ups and downs of hormones — cortisol, estrogen, testosterone, IGF — can be out of sync with each other, which may be the underlying cause of the increased risk. “They also sleep less and may have a compromised immune system because of lack of sleep,” she said. “So, melatonin is an important piece, but only one piece in the puzzle.”

    No definitive study on lifestyle differences that can occur with shift work has yet been done, although anecdotally it has been reported that diet is adversely affected. The concept of physician well-being is getting traction both ways: as a path to maintaining longer career duration and as a way of helping to ensure patient contact with a health care provider who is free of the exhaustion that can result from late-night hours.

    Lower levels of satisfaction were associated with the number of night shifts worked in a longitudinal study of more than 700 emergency physicians by the American Board of Emergency Medicine. (Ann Emerg Med 2008;51[6]:714.) Moreover, the sleep disturbances that result from shift work, among other factors, are linked to burnout. So are night shifts one of the underlying reasons for career dissatisfaction in emergency medicine? The data don't delineate cause and effect, but “intuitively I think that it is; that's what can happen,” said Dr. Cydulka, the lead author of the study, which began more than two decades ago.

    More recently, the same was found to be true for nurses. (Health Aff 2012;31[11]:2501.) And there was another finding in that study that many health professionals might consider seriously troubling: patient satisfaction scores went down on visits during night shifts. Presumably, being in a hospital at such an hour is tough on everyone.

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