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Research Rounds – Volume 2, Issue 6, December 2016

NIOSH Research Rounds is a monthly bulletin of selected research at the National Institute for Occupational Safety and Health.
Volume 2, Number 6 (December 2016)

Are Flight Attendants at Increased Risk for Breast Cancer?

During the course of their shifts, flight attendants face exposure to cosmic radiation at higher concentrations than the public generally experiences on the ground, may cross time zones, and work during normal sleeping hours. All of these work conditions raise questions about potential occupational health hazards. Cosmic radiation is a form of ionizing radiation. Ionizing radiation is linked to risks for cancer and reproductive effects, but there are uncertainties about risk from cosmic radiation at the levels and durations of occupational exposure that flight crews may experience. Similar uncertainties complicate scientists’ abilities to estimate similar risks from disruption of the body’s “time clock” and sleep cycle. At the National Institute for Occupational Safety and Health (NIOSH), scientists study these and other exposures in efforts to reduce uncertainty and better protect workers’ health and safety.

One of the potential health hazards associated with exposure to cosmic radiation and working during normal sleeping hours, or shift work, is breast cancer. In a new study in the Scandinavian Journal of Work, Environment & Health NIOSH investigators looked specifically at the question of whether a relationship exists between breast cancer and these work conditions, in addition to crossing time zones, while controlling for other factors that could affect breast cancer risk. They found that these work conditions were not statistically associated with an increased risk of breast cancer among flight attendants overall. Among a subset of flight attendants with three or more births, however, these work conditions were statistically associated with a significantly greater risk of breast cancer. Although the associations found in this study among women with three or more births were strong, this subset of women was small at 15% of the total study group. For this reason, more research is necessary to confirm these findings, according to the investigators.

In a previous study by the same investigators, flight attendants were more likely to be diagnosed with breast cancer than women in the general population.This increase seemed to be associated with beginning to have children later in life and to giving birth fewer times than women in the general population. Both of these factors are known risks for breast cancer in the general population.

In both studies, volunteer study participants included 6,093 former flight attendants in the United States. All participants were female, and their average age was 55. Through telephone interviews with participants, investigators obtained demographic information, including age, education, and work history; risk factors for breast cancer including number of births; and cancer diagnoses. They also obtained cancer diagnoses by linking to six state cancer registries and age and work history data from the airline company records. After estimating the amount of exposure to cosmic radiation, number of time zones crossed, and time spent working during normal sleeping hours for each participant, the investigators used statistical methods to assess potential links of these estimates to breast cancer incidence. As research continues to clarify the implications of work factors for aircraft crews, NIOSH offers precautionary recommendations for employers and workers at Aircrew Safety & Health.

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NIOSH Research Rounds is Brought to You By:
  • John Howard, M.D., Director
  • Fred Blosser, Editor in Chief
  • Anne Blank, Story Editor
  • Tanya Headley, Contributing Editor
  • John Lechliter, Copy Editor
  • Glenn Doyle, Technical Lead
  • Tonya White, Technical Support

Sleep Deprivation Affects Cognitive Function Similarly in Women and Men Working Shifts

Sleep deprivation associated with working during regular sleeping hours, or working shifts, can be detrimental to awareness and alertness. In turn, working around heavy equipment or behind the wheel can be dangerous if you’re not sufficiently alert. Less clear is whether or how other factors such as work stress and sleep quality interact with shift work to affect cognitive function. In addition, given gender differences in the processes involving sleep, health, and stress, it is also unclear if these factors may affect cognition differently in women and men.

To find out, investigators at the National Institute for Occupational Safety and Health (NIOSH) and their Canadian partners examined the relative effects of different variables on cognitive function, including work stress, shift work, and sleep quality. In a paper published in the peer-reviewed journal Occupational and Environmental Medicine, they reported that women generally had fewer hours of sleep, poorer sleep quality, and greater work-related stress compared to men. However, they found no difference between women and men in the effect of shift work on self-assessed cognitive function. Health and age also played an important role on cognition directly and through sleep. According to the investigators, these findings underscore the need for occupational health and safety programs that address cognitive function among all shift workers by focusing on stress, health, and sleep hygiene.

The study used data from 4,255 respondents to Canada’s National Population Health Survey in 2010. Participants’ average age was 43, and slightly more than half were women. All participants held jobs, with 75% working regular daytime hours and the remainder working either shift hours, rotating day and night hours, or on-call hours.

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Work-related Lead Exposure Unrelated to Thyroid Function in Men

Memory loss, weakness, irritability, and fatigue are just some of the obvious health effects of exposure to lead, but what about hidden risks? Of concern are the possible consequences of lead exposure on the thyroid gland and the hormones it produces, which are critical to cell function. Although studies have looked at this issue, a quantitative review, or meta-analysis, of the results of these studies was unavailable until now.

To address this research gap, an investigator at the National Institute for Occupational Safety and Health (NIOSH) reviewed 16 studies of lead-exposed workers. Each study measured the blood concentrations of the two major thyroid hormones, thyroxine and triiodothyronine, as well as a thyroid-stimulating hormone, which is produced by the pituitary gland and acts on the thyroid gland. The analysis, published in the American Journal of Industrial Medicine, showed that the average level of thyroid hormones in the blood was similar between workers exposed to lead on the job and those who were not exposed. In addition, the analysis did not find a link between duration of work-related exposure to lead and blood concentration of thyroid hormones. Since the studies in the analysis included few women, the effects of work-related lead exposure on thyroid hormone levels in this group remain unclear, and future research should include adequate numbers of women.

Fortunately, work-related exposure to lead is less common today than in past years, since many consumer products no longer contain the toxic metal. Certain industries, however, such as construction, mining, and manufacturing, still use lead-containing materials, posing a risk of exposure to workers. To prevent exposure, NIOSH recommends wearing proper personal protective equipment, such as goggles, gloves, boots, and protective clothing. Other recommendations on the NIOSH website include showering and changing clothes and shoes after working around lead and lead dust.

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