How Does Working the Night Shift Affect the Brain?

New research suggests working evening shifts, night shifts, or rotating shifts may impact brain function, leading to cognitive impairments.

Humans are a primarily diurnal species, meaning they are awake and active during the day and sleep at night. However, businesses are open, and most of the world operates 24/7. So, some humans have work hours that fall outside the typical 9 a.m. to 5 p.m. day shift.

But, according to research, evening, night, and rotating day/night shifts may harm a person's wellbeing. For example, a 2021 study found links between night shift work, poor-quality sleep, and family and social life disruptions. In addition, 2022 research suggests that rotating night shifts may decrease the odds of healthy aging.

What's more, another study published in 2022 found that night shift workers had an increased body mass index (BMI), waist circumference, and immune cell counts compared to non-shift workers — especially if they worked many night shifts per month.

Now, a new study published on August 23 in PLOS One found associations between night and rotating shift work and overall cognitive impairment — specifically, impairments in memory and executive function.

For the investigation, scientists analyzed 47,811 middle-aged and older adults ages 45 to 85 years using data from the Canadian Longitudinal Study on Aging database.

The team examined whether the participants were ever exposed to shift work and, if so, their exposures during their longest job or current position.

The results revealed that about one in five participants had been exposed to some form of shift work during employment.

Then, the participants completed four cognitive function tests to determine memory and executive function.

After adjusting the results for age, sex, and education, the researchers found that night shift work, either currently or during the longest job, was associated with overall cognitive impairment compared to daytime work.

Specifically, night shift work during the longest job was linked to memory function impairment. Moreover, impairment in executive function was associated with current rotating shift work and rotating shifts during the longest job.

The scientists also found that memory and executive function impairments were significantly higher among non-white workers or workers with depression. However, older or higher-income workers were less likely to experience these shift work-related impairments.

Current smokers and individuals with obesity also had a higher likelihood of cognitive impairment.

Still, the scientists did not evaluate the participants' job types, the number of consecutive night shifts they worked, or the number of days off between shifts, so it's unknown whether these factors would change the findings.

Why would working night shifts induce cognitive impairments?

The study authors speculate that night shifts may cause repeated disruptions of the circadian rhythm which could result in sleep deprivation, daytime sleepiness, and brain inflammation — leading to cognitive decline.

In addition, circadian rhythm disruptions may cause physiological stress and increased cortisol levels, which could play a role in brain function.

The scientists also say circadian rhythm disturbances have been linked to neurodegeneration.

To clarify the reasons behind these findings, the researchers say more investigations are needed to look deeper into how working night shift affects the brain and the potential relationship between night shift work and cognitive decline.