For decades, scientists have known that not getting enough physical activity can jeopardize brain health and dwindle cognitive performance over time. What hasn't been fully understood is exactly why exercise can buffer aging's toll on the brain.
A recent study further complicates the relationship between physical activity and cognition. It found that having a desk job could be a pathway for preserving cognitive health.
After tracking over 8,500 men and women for more than a decade, researchers discovered that people with less active so-called "desk jobs" have a lower risk of developing poor cognition. The physically active manual workers were three times more likely to exhibit poor cognitive performance on tests in the study than the less active, "desk job" group.
This doesn't mean sitting all day is exactly good for you: The desk job workers who were not active outside after working hours also had a higher risk of poor cognition.
Spending day after day at the office may seem like a counterintuitive way to preserve brain health. However, these findings suggest that the mental stimulation office jobs can offer some protection.
"Physical activity during leisure may be protective for cognition, but work-related physical activity is not protective," the researchers write. Their findings were published Tuesday in the International Journal of Epidemiology.
The study — Researchers harnessed data from the EPIC-Norfolk Cohort, a population-based longitudinal study. The team analyzed data collected from 8,585 men and women who were between 40 and 79 years old in 1993 when the study began.
To untangle the connection between physical activity level and cognition, participants completed a detailed health and lifestyle questionnaire which surveyed how much, what type, and how frequently they were physically active during both work and leisure. The participants also underwent a health examination, which documented any cancer, heart disease, diabetes, or health complications they might have.
About twelve years after the initial data collection, participants returned to the lab and underwent similar health tests along with a battery of cognition tests. These tests measured their memory, attention, visual processing speed, reading ability, and IQ.
Across the board physical activity was not correlated with levels of cognitive performance. But when the researchers broke the data down by physical activity during work or leisure time, certain patterns emerged.
Being inactive during leisure time seemed to increase the risk of poor cognitive performance. Meanwhile, work-related physical activity was associated with an increased risk of poor cognitive performance, compared to physically inactive occupations.
People with inactive occupations, "office jobs," had a lower future risk of poor cognition and were more likely to have higher performance in cognitive tests in later life. This finding was especially true with men.
Individuals with no academic degrees were also more likely to have physically active jobs, but less likely to be physically active outside of work.
"Our analysis shows that the relationship between physical activity and cognitive is not straightforward," study co-author Shabina Hayat, a public health researcher at the University of Cambridge, explains. "While regular physical activity has considerable benefits for protection against many chronic diseases, other factors may influence its effect on future poor cognition."
Hayat and her colleagues hypothesize that less active jobs have a positive effect on brain health because they are more cognitively demanding. More research is needed to say for sure.
"People who have less active jobs — typically office-based, desk jobs — performed better at cognitive tests regardless of their education," Hayat says. "This suggests that because desk jobs tend to be more mentally challenging than manual occupations, they may offer protection against cognitive decline."
More research is needed to understand the confounding factors that might color these results, including lack of access, space, and time for physical activity outside of work, mental and physical stimulation of a job, and education. But what is clear, based on this study, is there's no one-size-fits-all prescription for physical activity. Generally, regular movement is key to preserve cognitive function across a lifespan.
LONGEVITY HACKS is a regular series from Inverse on the science-backed strategies to live better, healthier, and longer without medicine.
HOW THIS AFFECTS LONGEVITY — The study shows mentally stimulating activities at work and physical activity outside the office can help keep people mentally sharp as they age.
WHY IT'S A HACK — At work or during time off, anyone can engage in these activities whether it's a crossword puzzle, complex problem, or puzzle.
SCIENCE IN ACTION — Playing a sport, learning a language, or traveling are all activities that have been linked with healthy brain aging.
HACK SCORE OUT OF 10 — 🧠🧠🧠🧠🧠🧠6/10 smarter, better, faster, stronger brains.
Background: The current evidence for higher physical activity and better cognitive function and lower risk of dementia is strong but not conclusive. More robust evidence is needed to inform public-health policy. We provide further insight into discrepancies observed across studies, reporting on habitual inactivity including that during work.
Methods: We examined cross-sectional and prospective relationships of physical inactivity during leisure and occupation time, with cognitive performance using a validated physical-activity index in a cohort of 8585 men and women aged 40–79 years at baseline (1993–1997) for different domains using a range of cognitive measures. Cognitive testing was conducted between 2006 and 2011 (including a pilot phase 2004–2006). Associations were examined using multinomial logistic-regression adjusting for socio-demographic and health variables as well total habitual physical activity.
Results: Inactivity during work was inversely associated with poor cognitive performance (bottom 10th percentile of a composite cognition score): odds ratio (OR) 1⁄4 0.68 [95% confidence interval (CI) 0.54, 0.86], P 1⁄4 0.001. Results were similar cross-sectionally: OR 1⁄4 0.65 (95% CI 0.45, 0.93), P 1⁄4 0.02. Manual workers had increased risk of poor performance compared with those with an occupation classified as inactive. Inactivity during leisure time was associated with increased risk of poor performance in the cross- sectional analyses only.
Conclusions: The relationship between inactivity and cognition is strongly confounded by education, social class and occupation. Physical activity during leisure may be protective for cognition, but work-related physical activity is not protective. A greater under- standing of the mechanisms and confounding underlying these paradoxical findings is needed.