The distance from the back door of my house to the front door of my workplace, when measured in steps, totals about 2,000. I know this because I counted them one day last winter when an overnight snowfall rendered my normal mile-long bicycle commute imprudent. That means my total steps easily eclipsed 4,000 for the day but fell far short of the 10,000 strides fitness experts tend to obsessively recommend for optimal health.
The results of a study released last week, however, suggest that a shorter daily trek may still offer some benefits. Indeed, researchers believe it could delay the onset of dementia.
Neurologist Jasmeer Chhatwal, MD, PhD, and his team at Mass General Brigham hospital reviewed the physical activity and cognitive function of nearly 300 older adults and concluded that even moderate daily step counts kept dementia at bay when compared with more sedentary behavior. Those who took 3,000 to 5,000 steps per day maintained their cognitive function three years longer on average; those who reached 5,000 to 7,500 daily steps remained cognitively unimpaired for seven years longer.
“This sheds light on why some people who appear to be on an Alzheimer’s disease trajectory don’t decline as quickly as others,” says Chhatwal. “Lifestyle factors appear to impact the earliest stages of Alzheimer’s disease, suggesting that lifestyle changes may slow the emergence of cognitive symptoms if we act early.”
Analyzing data from the Harvard Aging Brain Study involving participants with an average age of 72 and no dementia symptoms at the beginning of the 14-year study, Chhatwal’s team examined brain scans for signs of amyloid-beta plaque and tau tangles and reviewed physical activity levels recorded on waistband pedometers. Annual cognitive assessments and additional brain scans combined to offer some novel — and not so novel — conclusions.
There’s already ample research indicating a salutary association between physical activity and cognitive function, though Chhatwal’s study breaks some new ground on the ability of moderate exercise to delay the development of dementia. The results also suggest that the benefits may plateau after 7,500 daily steps.
More interestingly, the research suggests that it was the accumulation of tau in the brain, rather than a buildup of amyloid-beta plaque, that responded to the exercise and delayed the onset of the disease. Much of Alzheimer’s research in recent years has focused on reducing plaque as a way of slowing cognitive decline, but Chhatwal’s team found that even participants with high levels of amyloid-beta at the beginning of the study were able to delay cognitive impairment by taking more steps.
“We demonstrated a new relationship between physical activity and longitudinal tau burden, where higher step counts were associated with slower early neocortical tau accumulation in individuals with elevated baseline [amyloid-beta],” Chhatwal writes in Nature Medicine. “These observational findings support a potential role for physical activity in modifying the [Alzheimer’s disease] pathological cascade, which remains to be confirmed in future randomized clinical trials.”
Mayo Clinic neurologist David Knopman, MD, hopes that further research clarifies the question of causality. He suggests that, rather than the exercise reducing the amount of tau in some participants, it could be that their brains didn’t initially host enough tau — which has been shown to affect motivation — to hinder them from taking the steps.
“What I’m saying actually is not that I doubt what they [did]. I just have a nagging anxiety that the causality runs in the other direction,” he tells STAT News. “I can’t prove they’re wrong, and they can’t prove they’re right.”
Chhatwal does point out that researchers found no link between exercise and cognitive function among participants at the start of the study, so it’s not likely that a lack of tau in some participants at the outset played a role in the results. But an observational study is, well, observational. It can’t prove cause and effect. More research, as they say, is needed.
I’m not one of those people who fixates on fitness trackers to monitor every move, so even if future studies happen to corroborate Chhatwal’s findings and public health experts admit that 10,000 steps a day may not be necessary to protect our aging brains, I doubt that I’ll start obsessing over my daily strides.
I do keep track of some things, however. I’ve traveled almost 500 miles on my bike so far this year, for instance, which I’m guessing hasn’t damaged my cognitive capacity. I am, after all, smart enough to leave my bike in the garage after a snowstorm.
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