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Taxi drivers and ambulance drivers -- two groups of people with jobs that require frequent spatial and navigational processing -- had the lowest proportions of deaths attributed to Alzheimer's disease, an analysis of U.S. death certificates showed.

Of nearly 9 million people who had died with occupational information, 3.88% had Alzheimer's disease listed as a cause of death. However, only 1.03% of taxi drivers and 0.74% of ambulance drivers died from Alzheimer's disease, according to research led by Anupam Jena, MD, PhD, of Harvard Medical School and Massachusetts General Hospital in Boston.

Of 443 occupations, ambulance drivers (0.91%) and taxi drivers (1.03%) had the lowest proportion of deaths due to Alzheimer's after adjusting for age and other variables, Jena and colleagues reported in the , an annual collection of feature articles and original, peer-reviewed research.

Other types of dementia didn't show the same relationship as Alzheimer's disease. And other transportation-related jobs that didn't require as much real-time spatial and navigational processing didn't have the same results as taxi or ambulance drivers. Bus drivers, for example, ranked 263rd.

The hippocampus is the brain region used to create cognitive spatial maps, the researchers noted. Alzheimer's disease is associated with accelerated hippocampal atrophy.

"Our results highlight the possibility that neurological changes in the hippocampus or elsewhere among taxi and ambulance drivers may account for the lower rates of Alzheimer's disease," Jena said in a statement.

"We view these findings not as conclusive, but as hypothesis-generating," he added. "But they suggest that it's important to consider how occupations may affect risk of death from Alzheimer's disease and whether any cognitive activities can be potentially preventive."

The study was prompted by earlier research led by Eleanor Maguire, PhD, of University College London (UCL), that showed hippocampal changes in licensed taxi drivers over time.

In their earliest studies, the Maguire team discovered that London taxi drivers had than others who were similar in age, education, and intelligence. But it wasn't clear whether the brain changed after years of cognitive demands while navigating London's streets or whether taxi drivers already had larger than average hippocampi.

London cabbies must pass a rigorous test that requires them to know the irregular layout of about 25,000 streets within a 6-mile radius of Charing Cross train station and the locations of thousands of places. This spatial learning is known as acquiring "the Knowledge" and typically takes several years. When Maguire and colleagues examined the brains of taxi drivers preparing for the test, they found that those who successfully passed had an increase in gray matter volume in their posterior hippocampi from baseline and changes to their memory profile compared with controls.

"It was quite an important discovery because at that point, there had been no evidence of changes in the brain related to training or proficiency, or anything like that," said Hugo Spiers, PhD, also of UCL.

"There has been a whole field of research with birds, squirrels, and other animals looking at how the size of their brains are related to what they do," Spiers told 番茄社区app. "But this was a first in humans, a landmark study."

Jena and co-authors analyzed 8,972,221 death certificates in the U.S. National Vital Statistics System that were linked to occupation. Records were from January 2020 through December 2022; 16,658 deaths were among taxi drivers and chauffeurs, and 1,348 were among ambulance drivers.

Mean age at death was about 68 for taxi drivers and 64 for ambulance drivers. About 70% of both groups had a high-school education or less. Findings were adjusted for age at death, sex, race, ethnic group, and education.

Across the entire sample, 348,328 people were identified as having an underlying cause of death from Alzheimer's disease. In sensitivity analyses, ambulance and taxi drivers consistently had the lowest proportion of Alzheimer's disease mortality, even when the analysis was restricted to people who died at age 60 and older, or when Alzheimer's was specified as either an underlying or contributing cause of death.

The study was observational and doesn't establish causality, Jena and colleagues emphasized. It also could not account for unmeasured confounders, they acknowledged.

People at higher risk of developing Alzheimer's disease may be less likely to become taxi or ambulance drivers, but this was unlikely given that Alzheimer's symptoms typically develop after working age, the researchers said. In addition, death certificates may underestimate the number of deaths caused by Alzheimer's disease.

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