How many steps per day are most effective for dementia prevention?

My dog Jack and I are diligent about getting our 10,000 steps walking every day.  Many studies have shown that regular exercise reduces the risk of getting dementia including Alzheimer’s, but questions remain: How much exercise is enough? Is more exercise always better than less exercise? Does exercise still help in the later stages of dementia? 

Exercise helps reduce all-cause mortality, as well as death due to cardiovascular disease, cancer and diabetes. The evidence that exercise reduces the risk of getting dementia including Alzheimer’s is overwhelming. A seminal paper published in  JAMA Neurology in 2019 studied the effects of exercise in subjects with positive beta-amyloid PET scans but no cognitive impairment at the start of the study (pre-symptomatic Alzheimer’s disease). The study found that there was a significant interaction of physical activity with beta amyloid burden, such that greater physical activity was associated with slower beta-amyloid-related cognitive decline. Changes in brain volume were also associated with amount of exercise. Exercise seems to slow shrinkage of the brain, at least in the early stages.

Unfortunately, the beneficial effect of exercise in slowing the progression of dementia due to Alzheimer’s disease does not extend to the late stages of the disease. By this time, the horses are out of the barn. The brain is already severely damaged, and improvement or even stabilization may not be possible.

But what is the optimal amount of exercise for reducing risk of getting Alzheimer’s dementia? One of the most convincing studies addressing this question was published last year in JAMA Neurology. The investigators monitored 78,430 adults with an average age of 61 years and no evidence of cognitive impairment at the beginning of the study. Accelerometer-derived daily step counts were recorded with follow up for an average of 6.9 years and recorded as 1) total steps per day, 2) incidental steps (less than 40 steps per minute), 3) purposeful steps (40 steps per minute or more), and 4) peak 30-minute cadence (mean steps per minute recorded for the 30 highest, not necessarily consecutive, minutes in a day). The optimal dose (ie, exposure value at which the maximum risk reduction was observed) was 9826 steps (hazard ratio [HR], 0.49) and the minimal dose (i.e., exposure value at which the risk reduction was 50% of the observed maximum risk reduction) was 3826 steps (HR, 0.75). The bottom line for this elegant but somewhat complicated study is that our current recommendations for daily step count have been correct.  The optimal daily step count is just under 10,000, but benefit in slowing onset of dementia can still be seen with as few as just under 4,000 steps. Step counts greater than 10,000 do not add much benefit, but more concentrated exercise (i.e., purposeful steps vs incidental steps) does seem to be more effective.