Alzheimer’s Deaths Lower in Taxi Drivers, But Study Has Caveats

While the cause of Alzheimer’s disease (AD) is not yet known, it’s well established that both genetic and environmental factors can affect our risk of developing the neurodegenerative disorder.

A new study published in BMJ investigated whether occupations that engage specific brain regions more intensively could reduce the burden of AD.  

Are certain occupations associated with a reduced burden of Alzheimer’s?

Professions like taxi and ambulance driving depend on strong local navigation skills. In London, for instance, taxi drivers must pass the renowned “Knowledge Test” to secure their cabbie license.

A famous 2000 study by Maguire et al. identified navigation-related structural differences in the hippocampi of London taxi drivers compared to control participants. The hippocampus is an area of the brain responsible for processes relating to learning and memory, including spatial navigation. It is also a brain region that experiences severe atrophy – the loss of neurons – in AD.

“The same part of the brain that’s involved in creating cognitive spatial maps – which we use to navigate the world around us – is also involved in the development of AD,” said Dr. Vishal Patel, MD, MPH, a resident physician in the Department of Surgery at Brigham and Women’s Hospital and the lead author of the BMJ study.

“We hypothesized that occupations such as taxi driving and ambulance driving, which demand real-time spatial and navigational processing, might be associated with a reduced burden of AD mortality compared with other occupations,” Patel continued.

The researchers analyzed death certificates from the National Vital Statistics System in the US from 1 January 2020–31 December 2022. Death certificates included data such as the underlying cause of death and the individual’s occupation, enabling the identification of trends or associations between the two. Over 8 million deaths were assessed, with 3.8% of certificates listing AD as the primary cause.

From the cohort of ~8 million people, 16,658 were taxi drivers and 1,348 were ambulance drivers. Approximately 1.03% of taxi drivers and 0.74% of ambulance drivers had died from AD, which was the lowest proportion of deaths due to AD of all occupations examined. The authors noted that this trend was not found across other transport-related jobs, such as bus drivers (3.11%) or pilots of airplanes (4.57%).

Patel and colleagues emphasize that this study cannot prove causation as it adopted an observational methodology. Rather, they view it as a “hypothesis-generating” piece of work, senior author Dr. Anupam B. Jena, MD, physician in the Department of Medicine at Massachusetts General Hospital, said.

The scientific community seems to agree.

“This is a large study that adds to knowledge around building brain resilience to reduce the risk of AD,” Tara Spires-Jones, director of the Centre for Discovery Brain Sciences at the University of Edinburgh, group leader in the UK Dementia Research Institute and president of the British Neuroscience Association, told the Science Media Centre (SMC). “However, it is not possible from this type of data to conclude for certain that these occupations protect people from AD. It is possible that people who are at higher risk of Alzheimer’s may not choose memory intensive driving occupations, which is a so-called ‘selection bias’,” she continued.

Dr. Richard Oakley, associate director of research and innovation at Alzheimer’s Society, added that the data are not supported by brain scans that demonstrate changes in the brain: “It also overlooks that some people hold multiple jobs in their lifetime, and it doesn’t consider biological or social factors, such as genetics or socio-economic status, which could affect a person’s chances of developing AD, so it is difficult to draw any firm conclusions.”

A further limitation of the study is that the average age of death of taxi and ambulance drivers was 64–67 years. For other occupations analyzed, it ranged from 74 years (bus drivers) to 78 years (aircraft pilots).

“This is a serious limitation of the study as the age of onset of Alzheimer’s is typically after 65 years old, meaning that the taxi and ambulance drivers might have gone on to develop Alzheimer’s if they lived longer. Similarly, the proportion of women taxi and ambulance drivers was 10–22% whereas in all other occupations this was 48%. This is important because women are more likely to develop AD than men.  Authors used statistics to try and take into account these limitations, but they do limit the interpretation of the study,” Spires-Jones noted.

The experts agree that, despite the limitations, the data are interesting and call for fundamental research into how we might be able to protect our brains from AD.

Reference: Patel VR, Liu M, Worsham C, Jena AB. Alzheimer’s disease mortality among taxi and ambulance drivers: population based cross sectional study. BMJ. 2024. doi: 10.1136/ bmj-2024-082194