We can feel groggy when our sleep schedule is thrown off even just a little. So what happens when shift work requires people to regularly stay awake through the night and sleep during the day — and how can they protect their health and well-being?
What is shift work disorder?
Mounting evidence, including several new studies, paints a worrisome picture of the potential health fallout of nontraditional shift work schedules that affect 15% to 30% of workers in the US and Europe, including factory and warehouse workers, police officers, nurses, and other first responders.
So-called shift work disorder mainly strikes people who work the overnight or early morning shift, or who rotate their shifts, says Eric Zhou, an assistant professor in the Division of Sleep Medicine at Harvard Medical School. It is characterized by significant problems falling and staying asleep, or sleeping when desired. That's because shift work disrupts the body's normal alignment with the 24-hour sleep-wake cycle called the circadian rhythm.
"People who work 9-to-5 shifts are typically awake when the sun is up, which is aligned with their body's internal circadian clock. But for shift workers, their work hours and sleep hours are misaligned with the natural cues to be awake or asleep," Zhou says. "They're working against the universe's natural inclinations — not just their body's."
What's the connection between shift work and health?
A 2022 research review in the Journal of Clinical Sleep Medicine links shift work to higher risks for serious health problems, such as heart attack and diabetes. This research suggests adverse effects can include metabolic syndrome (a cluster of conditions that raises the risks for heart disease, diabetes, and stroke), accidents, and certain types of cancer.
"The research is consistent and powerful," Zhou says. "Working and sleeping during hours misaligned with natural light for extended periods of time is not likely to be healthy for you."
How do new studies on shift work boost our understanding?
New research continues to add to and strengthen earlier findings, teasing out specific health effects that could stem from shift work.
- Shift workers on rotating schedules eat more erratically and frequently than day workers, snack more at night, and consume fewer healthier foods with potentially more calories, a study published online in Advances in Nutrition suggests. This analysis reviewed 31 prior studies involving more than 18,000 participants, comparing workers' average food intake over 24 hours.
- Disrupting the circadian rhythm through shift work appears to increase the odds of colorectal cancer, a malignancy with strong ties to lifestyle factors, according to a 2023 review of multiple studies published online in the Journal of Investigative Medicine. Contributors to this higher risk may include exposure to artificial light at night, along with complex genetic and hormonal interactions, study authors said.
"Cancer understandably scares people, and the World Health Organization recognizes that shift work is a probable carcinogen," Zhou says. "The combination of chronically insufficient and poor-quality sleep is likely to get under the skin. That said, we don't fully understand how this happens."
How can you protect your sleep — and your health?
If you work overnight or early morning shifts, how can you ensure you sleep more soundly and restfully? Zhou offers these evidence-based tips.
Time your exposure to bright and dim light. Graveyard shift workers whose work schedule runs from midnight through 8 a.m., for example, should reduce their light exposure as much as possible after leaving work if they intend to go right to sleep once they return home. "These measures could take the form of wearing blue light–blocking glasses or using blackout shades in your bedroom," he says.
Make enough time for sleep on days off. "This is often harder than it sounds, because you'll want to see your family and friends during nonwork hours," Zhou says. "You need to truly protect your opportunity for sleep."
Maintain a consistent shift work schedule. "Also, try to minimize the consecutive number of days you spend working challenging shifts," he says.
Talk to your employer. Perhaps your boss can schedule you for fewer overnight shifts. "You can also ask your doctor to make a case for you to be moved off these shifts or have more flexibility," Zhou says.
Look for practical solutions that allow you to get more restful sleep. "People engaged in shift work usually have responsibilities to their job as well as their family members, who often operate under a more typical 9-to-5 schedule," he notes. "The goal is to preserve as strong a circadian rhythm as possible under the abnormal schedule shift work requires."