Even gentle exercise like walking boosts brain health
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Older people who are particularly at risk of Alzheimer’s disease could slow their cognitive decline by taking just 3000 steps a day. Why this step count might have this effect is unclear, but it could be linked to the impact of regular exercise on inflammation or blood flow to the brain.
Prior studies that link regular exercise to reduced cognitive decline have mostly relied on people recalling their activity levels and have rarely explored why staying active may have this effect.
To address such limitations, Wai-Ying Wendy Yau at Harvard University and her colleagues analysed the physical activity of 296 cognitively-healthy people, aged between 50 and 90, who wore a step-tracking device for one week, to objectively measure their activity levels.
Most of the participants had their brain imaged to reveal their baseline levels of misfolded proteins called tau and beta-amyloid, clumps of which are thought to cause Alzheimer’s. These levels were then generally measured every two to three years over a follow-up period of between three and 14 years. The participants also completed annual cognitive tests that assessed things like their memory and how quickly they processed information.
By feeding the step count, brain imaging and cognitive test data into a statistical model, the researchers estimated how exercise affects cognitive decline. They found that, among the participants with above-average levels of misfolded beta-amyloid in their brain at the start, taking between 3000 and 5000 steps per day seemed to substantially slow the accumulation of misfolded tau, but not beta-amyloid.
“[Exercise is] somehow slowing the spread of this tau protein, which is more strongly associated with people developing symptoms [of Alzheimer’s disease] than amyloid-beta,” says Charles Marshall at Queen Mary University of London.
This was also linked to their rate of cognitive decline slowing by about 40 per cent over an average follow-up period of nine years, compared with taking fewer than 3000 steps per day, defined as being inactive. The researchers lacked the data to assess whether any of the participants were diagnosed with Alzheimer’s disease during the follow-up period.
Meanwhile, taking between 5000 and 7500 steps per day seemed to slow tau accumulation even further, leading to a 54 per cent slower rate of cognitive decline compared with being inactive. But taking more than 7500 steps per day wasn’t linked to further cognitive benefits. “Those tau and cognitive benefits eventually plateau,” says Yau.
The researchers didn’t explore exactly how regular exercise may have these effects, but it could be due to physical activity reducing inflammation, which is thought to occur as a consequence of misfolded beta-amyloid and tau, and then disrupt neural connections and kill cells. Exercise may also boost blood flow or levels of a protective hormone to the brain.
However, this study doesn’t prove that taking 5000 steps a day slows or delays cognitive decline. Existing impairments that haven’t yet been diagnosed or even noticed could affect people’s ability or motivation to exercise, says Marshall. Other lifestyle or socioeconomic factors, some of which the team attempted to adjust for, could also affect activity and tau levels, he says.
Nevertheless, regular exercise has a plethora of health benefits, can be done for free and has very few – if any – side effects, which might encourage people to take at least 3000 steps a day, despite the exact effects on cognitive function being unclear. “My advice to people is always not to fixate too much on a magic number for the [step count] goal,” says Marshall. “I think [what’s] more important is the idea of doing something regularly, and it doesn’t have to be a lot, and it doesn’t have to be high intensity, it’s more about doing some physical activity with high regularity.”
Previous research suggests that steadfast lifestyle changes – including exercise – improve cognitive decline. But further studies in which individuals are randomly assigned to achieve various daily step counts are needed to separate the effects of exercise from other lifestyle changes and establish whether they really do slow tau accumulation, says Yau.
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