An analysis of UK Biobank data comparing shift workers and non-shift workers found a pattern of reduced brain volume in the left amygdala and right thalamus regions of the brain. For those who stopped shift work, gradual volume loss stopped within 2.4 years. The paper is neuroimage.
Over the past few decades, human society has increasingly moved toward a model in which businesses and service providers are expected to operate 24 hours a day. This increased the number of people working in shifts. A recent study found that the proportion of workers in Europe who work in shifts increased from 17% in 2010 to 21% in 2015 and remained stable until 2024. In the United States, the proportion of shift workers increased from 14.8% in 2004 to 16.4% in 2019. At the same time, the workforce is aging significantly.
Research has shown that shift workers often experience an increase in health problems because night shifts and shift work disrupt the body’s circadian rhythms and sleep patterns. This can lead to lack or poor quality of sleep, fatigue, stress, negative mood, and increased risk of accidents. Over time, shift work has been linked to an increased risk of cardiovascular disease, diabetes, obesity, gastrointestinal disease, depression, and some cancers. People who work a lot of night shifts or shifts are usually at higher risk because their bodies have less time to adapt.
Study author Thomas Welton and his colleagues hypothesized that shift work may be associated with reduced volume in certain areas of the brain and abnormal microstructure of brain tissue. They also proposed that cessation of shift work would be associated with a cessation of work-related changes in brain structure, and that the effects of shift work on brain structure would be correlated with number of hours worked and cognitive impairment.
These authors analyzed data from the UK Biobank accessed via the UK Biobank Research Analysis Platform. The UK Biobank is a population-based biobank of over 500,000 people aged 40–70 years recruited from the general UK population between March 2006 and July 2010. One of the 22 assessment centers included all participants at the start of the study (2006-2010), some participants at the first imaging visit (2014 onwards), and some of those participants at the repeat imaging visit (2019 onwards).
Data used in this analysis were from participants who completed brain magnetic resonance imaging at their first imaging visit, had no diagnosis of cancer, stroke, heart attack, or other serious medical condition, rated themselves as in at least fair health, and were in full-time paid employment or self-employment. The absence of incidental findings from magnetic resonance imaging scans was also required.
Data from a total of 14,198 individuals were included in this analysis, of which 2,122 were shift workers. The median age of participants was 47 years. Data on whether participants worked shifts was obtained from a question asking how often they worked shifts. Those who answered “always,” “usually,” or “sometimes” are considered shift workers.
The results showed that shift workers showed a symmetrical pattern of tissue volume reduction in the right thalamic and left amygdala regions of the brain. The difference with non-shift workers was very small but detectable (i.e., statistically significant). Remarkably, the researchers also found a “dose-response” relationship. This means that as the frequency of a person’s shift work increases, the volume of the amygdala further decreases.
For participants who stopped shift work between two imaging visits, the analysis revealed that shift work-related volume loss stopped within 2.4 years and there was even a slight volume recovery. Additional analyzes revealed microstructural deterioration in the corticospinal tract, cerebral peduncle, and right sagittal region in shift workers. Additionally, shift workers tended to have lower scores on tests measuring memory, fluid intelligence, and mental processing speed.
“Shift workers exhibit selective volume reductions in the thalamus and amygdala, but this decline stops within 2.4 years of ceasing shift work. Intervention measures, including monitoring, counseling, and adjustment of work schedules, may minimize brain volume loss in shift workers,” the study authors concluded.
This study contributes to the scientific understanding of the potential physiological effects of shift work. However, we note that the design of this study does not allow definitive causal inferences to be drawn from the results. The volume changes detected were very small, and UK Biobank participants were generally healthy and less diverse than the wider population.
The paper, “Shift work is associated with selective brain volume reduction: a longitudinal study,” was authored by Thomas Welton, Thomas Wei Jun Teo, Said Ethan Safari, Linlin Zhang, and Eng King Tan.
