Key points
- Shift workers labor at night when others usually sleep, potentially disrupting their circadian rhythms – also called “body clocks” – which determine sleeping and feeding patterns.
- 63 percent of shift workers said their work schedule allows them to get enough sleep, compared with 89 percent of regular workers, according to a 2008 National Sleep Foundation survey.
- Recent studies have explored shift workers’ dietary habits and whether they contribute to disrupted body clocks and chronic inflammation.
Judith Simcox became interested in shift worker health when her mother, a night-shift nurse in Montana, was diagnosed with breast cancer.
Her mother exercised and was at a healthy weight, and her family did not have a history of the cancer. She worked nights so she would be available during the day to take care of Judith’s sister, who has Down syndrome and type 1 diabetes.
Simcox learned that research has connected shift work – which NIOSH defines as working outside the typical daylight hours of 7 a.m. to 6 p.m. – to a variety of health disorders, including diabetes, cancer and hypertension.
“I was shocked no one had told her doing shift work predisposed her for this,” Simcox said. “I think she would have still worked the same amount of hours, but been more careful with [medical] screening.”
As a postdoctoral fellow in biochemistry at the University of Utah in Salt Lake City, Simcox led a recent study that suggested shift workers avoid eating high-iron foods at night to help prevent abnormal blood glucose levels. She hopes to conduct further research to provide guidelines for shift workers.
“Shift work is part of the forgotten population,” Simcox said. “They’re your nurses, doctors, people working in factories. They’re very fundamental to society and taking risks.”
Disrupting the body clock
Shift workers labor at night when others usually sleep, potentially disrupting their circadian rhythms – also called “body clocks” – which determine sleeping and feeding patterns. The International Agency for Research on Cancer in 2007 classified shift work involving circadian disruption as a “probable carcinogen.”
“Our internal body clock can become misaligned with signals from the environment,” said Dr. Natalie Dautovich, environmental scholar for the National Sleep Foundation and assistant professor of clinical psychology at the University of Alabama in Tuscaloosa. “As a result, we might feel sleepy when we should feel alert. We might feel alert when we’re supposed to be asleep, similar to a jet-lag experience. It can be difficult for people to get the quantity and quality of sleep they need due to environmental factors, such as trying to sleep when it’s light outside, noisy, etc.”
In a 2008 NSF survey, 63 percent of shift workers said their schedule allowed them to get enough sleep, compared with 89 percent of traditional workers.
“When we’re sleeping, our bodies repair things,” said Dr. Christina Lawson, an epidemiologist with NIOSH. “Rest is really something that helps us stay healthy, so when we do night-shift work [we] alter those sleep-wake patterns and daytime-darkness patterns that can affect our health, our ability to recover.”
The effects of diet
Simcox and other researchers at the University of Utah fed iron to mice to observe how the liver’s circadian clock becomes out of sync with the brain’s circadian clock – potentially resulting in metabolic disorders such as obesity and diabetes. The study was published in October in the journal Diabetes.
Eating food sets the liver’s circadian clock. The researchers found that intake of iron increases the cellular concentration of heme, an iron compound in hemoglobin.
When heme binds to a circadian protein, the protein’s activity increases and prompts the liver to properly control blood glucose levels. But if the protein’s activity increases when the circadian clocks are out of sync, abnormal blood glucose levels may result, according to the study. So if a shift worker eats high-iron foods at night, lack of synchronization between the clocks in the liver and the brain could become worse.
Simcox recommends that shift workers avoid high-iron foods – such as steak, other red meat and spinach – at night, noting that workers could eat those foods or take an iron supplement during the day to keep their body clocks synchronized. “It’s not an idea of iron is bad,” she said. “It’s when you’re eating iron.”
A study from the University of South Carolina published in February 2014 in the Journal of Occupational and Environmental Medicine also explored shift workers’ dietary habits. Shift workers are more likely to eat a diet promoting chronic inflammation, which could partly explain the association between the work and certain diseases, researchers concluded.
They calculated workers’ dietary inflammatory index, which measures how likely it is for the worker’s diet to cause inflammation. A pro-inflammatory diet is high in fats, carbohydrates and sweets. Researchers found shift workers had an elevated DII compared to day workers, and the difference was significant for workers whose shifts varied.
“The odds are the diet is working with other behavioral habits, which can influence health and disease among shift workers,” said Dr. Michael Wirth, lead author and research assistant professor at the University of South Carolina in Columbia.
Chronic inflammation contributes to diseases such as cancer and cardiovascular disease, Wirth said. Shift workers are prone to eat a pro-inflammatory diet because they work when they normally would be asleep, so they tend to crave energy-dense foods high in calories, fat, protein and carbohydrates – and few healthy food outlets are open in the middle of the night, he added. Instead, shift workers should seek healthier options, such as fruits and vegetables, and undergo medical screenings, he said.
Photo credits: Background image: STILLFX/iStock/Thinkstock; doctor photo: ColorBlind Images/Blend Images/Thinkstock; factory photo: dominiquelandau/iStock/Thinkstock; worker photo: Fuse/Thinkstock
Next page: Tips, other studies and guidance
Tips for workers and employers
A NIOSH blog post on shift work offers guidance for both workers and employers.
For employers:
- Set aside at least 10 straight hours per off day so workers get seven to eight hours of sleep.
- Allow frequent, brief breaks (every one to two hours) during demanding work. These breaks are more effective against fatigue than a few longer breaks. Allow longer breaks for meals.
- Be aware that five eight-hour shifts or four 10-hour shifts per week are usually tolerable. Twelve-hour days may be tolerable with more frequent, scattered rest days. Shorter shifts (eight hours) at night are more tolerable.
- Examine work demands. Twelve-hour shifts are more tolerable for “lighter” tasks, such as desk work.
- Plan one or two full days of rest after five straight eight-hour shifts or four 10-hour shifts. Consider two rest days after three straight 12-hour shifts.
- Provide training so workers are aware of resources to help with any difficulties of shift work.
- Examine near misses and incidents to determine the role fatigue may have played.
For workers:
- Make sure you have enough time to sleep after work.
- Avoid heavy food and alcohol and reduce intake of caffeine and other stimulants several hours before sleep.
- Exercise routinely.
- Sleep in a place that’s dark, comfortable, quiet and cool.
- Seek help from a health care provider if you are experiencing sleep problems.
For more information, go to http://blogs.cdc.gov.
Other studies
A sampling of recent research on shift work and its health effects:
- A study published in January 2013 by the Fred Hutchinson Cancer Research Center in Seattle connected shift work to ovarian cancer.
- A study published in July 2014 by Huazhong University of Science and Technology in China linked shift work to an increased risk of type 2 diabetes.
- A study published in October 2014 by the Weizmann Institute of Science in Israel suggested that disruption in the body’s circadian clock through shift work or frequent flights across time zones disrupts gut microbes, resulting in obesity and metabolic issues.
- A study published in November 2014 by the University of Toulouse in France concluded that performing shift work for many years can result in diminished brain power, and a worker would need at least five years to recover.
Guidance
As researchers continue to explore the effects of shift work on health, employers can help, Lawson said. Businesses could provide services such as healthy food options and workout facilities. Policies that incorporate naps, rest time and flexible schedules are other possibilities.
Workers need to prioritize sleep and take into consideration factors such as napping and caffeine intake, Dautovich said. “For a shift worker, considering their bedroom environment may be even more critical, making sure the bedroom is designed to help them wind down, avoiding electronics, controlling light perhaps through blackout curtains, eliminating or masking noise with a sound conditioner,” she said.
Lawson encourages workers to understand the importance of sleep and share that information with their family and others to help reduce conflicting demands.
“Speak up for yourself with your employer if you’re finding yourself too fatigued to drive home or too fatigued to safely do your job,” she said. “That’s important, to try to advocate for yourself.”
Photo credits: Background image: STILLFX/iStock/Thinkstock; doctor photo: ColorBlind Images/Blend Images/Thinkstock; factory photo: dominiquelandau/iStock/Thinkstock; worker photo: Fuse/Thinkstock
