THE ARISING · Longevity & Healthspan
Fittest Adults Had About Half the Dementia Risk in 2.3-Million-Person Review
Adults in the top fitness group had roughly half the risk of developing dementia of those in the bottom group, according to a pooled analysis of more than 2.3 million people published in GeroScience.
The work is a systematic review and meta-analysis of observational cohort studies. It combined 13 articles from 12 unique studies, covering 2,317,053 adults in the general population. Each study followed participants for at least one year. The researchers searched the MEDLINE and Embase databases and registered their review plan.
The measure was cardiorespiratory fitness: how well the heart and lungs deliver oxygen to working muscles. The studies expressed it in METs, a unit that scales with how much physical work a person's body can sustain. Higher MET values mean higher fitness.
Nine studies, with 2,276,366 participants and 47,796 dementia cases, compared the top fitness group with the bottom. After adjustment for other factors, the pooled risk ratio was 0.53 (95% confidence interval 0.44 to 0.64). That is about 47% lower risk of dementia in the fittest group.
The link also held as a gradient. For each 1-MET increase in fitness, the risk ratio for dementia was 0.93 (95% confidence interval 0.90 to 0.95), or about 7% lower risk per step. Fitness is measured on a scale, not simply as fit or unfit. This association does not mean that increasing fitness by one MET necessarily reduces an individual's dementia risk by 7%.
Two studies, with 1,184,604 participants and 609 cases, looked at cognitive impairment. The top fitness group had a risk ratio of 0.63 (95% confidence interval 0.42 to 0.93).
Four studies tracked fitness over time. In those, increasing fitness or maintaining a higher level was associated with a lower risk of dementia or cognitive impairment. The finding suggests the trajectory may matter, not only a single measurement.
Alzheimer's disease is the open question. Two studies with 300 cases gave a risk ratio of 0.35, but the confidence interval ran from 0.07 to 1.83, which is too wide to support a firm conclusion about that disease alone.
The authors conclude that higher cardiorespiratory fitness may be associated with reduced risk of incident dementia and other cognitive outcomes in the general population. All participants were free of cognitive problems at the start.
Next to watch: further cohort studies that measure fitness repeatedly, and larger datasets on Alzheimer's disease specifically.
These studies followed people rather than assigning exercise. They cannot show that exercise itself halves dementia risk, and other differences between fitter and less fit people may help explain the association. The estimates describe relative differences between groups, not a person's absolute chance of developing dementia.