Routinely working outside of a normal, daytime shift may cause cognitive and memory impairment, according to a new study.
The new research builds on a bank of analysis that’s beginning to reveal the ways in which shift work, particularly rotating and night shift work, impacts the brain and body over time.
“It’s important to know this is a multifactorial issue. There’s not just one system that is being impacted,” said Durdana Khan, PhD, a doctoral scholar at York University in Canada, who led the new research. “Stress, sleep deprivation, and melatonin disruption all work on the brain.”
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It’s estimated that around one-quarter of adults in the United States, or nearly 40 million people, are or have been shift workers—either working nights or rotating between night and day shifts.
Previous studies have linked long-term shift work to a slew of health problems including coronary artery disease and atypical heart rhythms, obesity, cancer, type 2 diabetes, and even a later onset of menopause.
To better understand how an abnormal work schedule impacts the brain, Khan and her team analyzed data from the Canadian Longitudinal Study on Aging, including nearly 48,000 middle-aged and older adults ages 45 to 85 years old.
They evaluated whether each person had ever worked shift work; if so, whether they worked shifts during their longest job, and whether they were currently working shift work.
They found that about one-fifth of people in the study had worked shift work at some point. People who worked the night shift, either at their current job or the job they held for the longest amount of time, were more likely to have overall cognitive impairment.
Compared to people who consistently work during the day, working the night shift during a person’s longest job was associated with memory impairment.
Those who worked rotating shift work—sometimes working day shifts and sometimes working nights—were more likely to have impaired executive function, a mental process that allows people to plan, focus attention, remember, and multitask.
According to Beth Malow, MD, a professor of neurology at Vanderbilt University and Director of the Vanderbilt Sleep Division, the primary way shift work impacts the brain is by disrupting sleep patterns by requiring people to be awake and working some nights, and asleep others.
This misalignment to the body’s biological rhythms causes the brain to release different chemicals, including stress hormones, which can affect memory over time.
Humans have a 24-hour biological clock that regulates a number of physiological processes including sleep patterns, eating and digesting, blood pressure, body temperature, and how hormones are regulated.
“It’s less about the duration of the shift and more about the circadian misalignment,” Malow told Health.
According to Malow, people need to get a good night’s sleep to think clearly and to allow the brain to reset and get rid of toxic proteins that can build up in the organ and affect memory.
“However, the impact of shift work goes beyond sleep to cause circadian misalignment,” she said.
According to Khan: “Shift workers are working when our bodies need rest. In scientific language, it’s called desynchronization of our body, there is an imbalance, and a lot of things are happening when there is imbalance in our body.”
The brain responds to darkness—the sun going down—by preparing the body for sleep. This includes releasing melatonin, a hormone that promotes sleep.
When people work at night, they’re often exposed to light when their bodies would otherwise be winding down for bed. This disrupts the natural circadian rhythms.
After repeated exposures, these disruptions are harmful to the body and have a direct effect on brain cells, leading to neurodegeneration, said Khan.
When the natural sleep schedule is disrupted, it also causes the brain to release inflammatory proteins at abnormal levels. While the body naturally produces some amount of these inflammatory proteins, sleep disruption can prompt the brain to produce too many, “Which has neurotoxic effects on brain cells, which can impair brain function,” Khan said.
Cortisol is another way in which disrupted sleep patterns during shift work can have toxic effects on the brain.
Lack of sleep naturally causes an influx in cortisol, the body’s stress hormone. If someone’s job is stressful on top of being shift work, for example, nursing, this can compound the negative impact cortisol has on the brain.
Although people who work at night do appear to have more cognitive impairment than people who work during the day, Khan explained that having an irregular schedule that shifts between working during the day and working at night likely has the most profound impact on cognitive function.
“This rotating shift work is more disruptive to your body because you’re not giving your body a chance to adjust,” she said. “If you are doing regular night shifts, your body can adjust.”
For many, shift work is an unavoidable part of their job. Malow emphasizes the importance of getting as much sleep as possible, even when a person’s schedule requires them to do so sporadically or during the day.
If at all possible, she said it’s important to stick to a sleep schedule, that is, sleeping around the same time every day. This may be more doable for people who only work night shifts, rather than rotating shift workers.
All shift workers should also focus on other pillars of health—eating a healthy diet and getting enough physical activity—to help mitigate some of the cognitive and physiological impacts of having an erratic sleep schedule.
“Not everyone can sleep during the day,” Khan said. “But after your shift work, there should be a resting period where you can relax.”
