Exploring shift worker health

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

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