People working in shifts undergo gradual shrinkage of two brain regions

An analysis of the UK Biobank data that compared people working in shifts with non-shift workers found a pattern of brain volume loss in the left amygdala and right thalamus areas of the brain. In individuals who halted shift work, the gradual volume loss stopped within 2.4 years. The paper was published in NeuroImage.

In the past decades, human societies have moved ever more towards a model where business and service providers are expected to operate 24 hours a day. This has caused an increase in the number of people who work in shifts. A recent study found that the proportion of workers working in shifts has increased in Europe from 17% in 2010 to 21% in 2015 and has remained stable through 2024. In the U.S., the proportion of shift workers increased from 14.8% in 2004 to 16.4% in 2019. At the same time, the workforce has become significantly older.

Studies have shown that shift workers often have increased health problems because working nights or rotating schedules disrupts the body’s circadian rhythm and sleep pattern. This can lead to insufficient or poor-quality sleep, fatigue, stress, negative mood, and higher accident risk. Over time, shift work has been linked to a greater risk of cardiovascular disease, diabetes, obesity, gastrointestinal problems, depression, and some cancers. The risks are usually higher for people who work night shifts or frequently rotating shifts, because their bodies have less time to adapt.

Study author Thomas Welton and his colleagues hypothesized that shift work might be associated with reductions in the volume of certain areas of the brain and with abnormal microstructure of brain tissues. They also proposed that the cessation of shift work would be associated with the halting of work-related changes to brain structure and that the effects of shift work on brain structure would correlate with the number of hours worked and with a cognitive deficit.

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 individuals aged 40–70 years who were recruited between March 2006 and July 2010 from among the general UK population. One of 22 assessment centers was attended by all participants at the start of the study (2006–2010), by a subset of participants for an initial imaging visit (2014+), and by a subset of those participants for a repeat imaging visit (2019+).

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Data used in this analysis came from participants who had completed magnetic resonance imaging of their brain during the initial imaging visit, had no prior diagnoses of cancer, stroke, heart attack, or other serious medical conditions, who rated themselves to be at least in fair general health, and were in full-time paid employment or self-employed. They were also required to have had no incidental findings from any of the magnetic resonance imaging scans.

In total, data from 14,198 individuals were included in this analysis, 2,122 of whom were shift workers. Participants’ median age was 47 years. Data on whether participants work in shifts came from a question asking them how often they work in shifts—those who answered “Always”, “Usually”, or “Sometimes” were considered to be shift workers.

Results showed that shift workers exhibited a symmetrical pattern of tissue volume loss in the right thalamus and left amygdala regions of the brain. The differences from non-shift workers were very small but detectable (i.e., statistically significant). Notably, the researchers also found a “dose-response” relationship, meaning that as the frequency of a person’s shift work increased, the volume of their amygdala decreased even further.

In participants who ceased shift work between the two imaging visits, analyses revealed a halting of shift work-related volume loss within 2.4 years, and even a slight recovery in volume. Additional analyses revealed microstructural degradation in the corticospinal tract, cerebral peduncle, and right sagittal stratum regions in shift workers. Furthermore, shift workers tended to score lower on tests measuring memory, fluid intelligence, and mental processing speed.

“Shift workers have selective volume loss of the thalamus and amygdala, which is halted within 2.4 years of stopping shift work. Monitoring, counselling and interventional measures, including adjustment of work schedules, could minimize brain volume loss in shift workers,” the study authors concluded.

The study contributes to the scientific understanding of potential physiological consequences of shift work. However, it should be noted that the design of this study does not allow any definitive causal inferences to be derived from the results. The volume changes detected were very small, and the UK Biobank participants are generally healthier and less diverse than the wider population.

The paper, “Shift work is associated with selective brain volume loss: a longitudinal study,” was authored by Thomas Welton, Thomas Wei Jun Teo, Seyed Ehsan Saffari, Ling-Ling Chan, and Eng King Tan.