Daily physical activity lowers Alzheimer’s disease risk in older adults

A lengthy walk can be a step in the right direction when you have concerns about your memory. A new long-term study indicates that getting up from your chair and moving around for a portion of the day may do even more than elevate your mood. It may slow the development of detrimental brain changes that begin decades before symptoms of Alzheimer’s emerge.

The researchers followed almost 300 older adults who had no signs of cognitive difficulty at the onset of the project. The participants wore simple pedometers, completed yearly memory tasks, and underwent brain scans during which researchers measured two important Alzheimer’s proteins: amyloid beta and tau. Some individuals were tracked for upwards of 14 years, providing scientists with a unique view into the slow and steady trajectory of hidden brain changes over time.

The most notable finding was how daily steps were tied to tau accumulation. Tau is a protein that develops tangles within brain cells and is closely associated with cognitive impairment, especially with respect to memory. More active people seemed to have slowed rates of tau accumulation, particularly for those with high levels of amyloid beta. Amyloid often elevates first and appears to create the environment for tau development.

Slower tau accumulation was also the best explanation for more active adults’ continued cognitive performance and independence. This was one of the clearest indicators that activity may impact the brain in ways that change daily life.

The study did not find any relationships between walking and amyloid levels. Individuals who engaged in more walking did not possess fewer amyloid deposits. Rather, activity may have affected what happened after amyloid had formed, slowing the rate of tau progression.

The amount of activity mattered: Participants were grouped based on the number of steps they took each day: fewer than 3,000, 3,001 to 5,000, 5,001 to 7,500, and more than 7,500. Even small distinctions resulted in measurable outcomes.

For example, participants who walked just above 3,000 steps rather than fewer than 3,000, declined in cognitive functioning consistently at 33 percent slower over time. Participants who walked 5,001 to 7,500 steps showed stronger results. Beyond 7,500 steps, there are diminishing returns, meaning that walking less than 10,000 steps could provide sufficient protective benefits without compromising your health.

“These findings provide insight to why some individuals who appear to be on an Alzheimer’s trajectory do not decline at the same rate as other individuals,” said Jasmeer Chhatwal, MD, PhD, of Mass General Brigham. “It seems that lifestyle factors play a role in the earliest stages of the disease process, which would also suggest that lifestyle factors may mitigate the emergence of cognitive symptoms if acted on early.”

Each of these values provides an optimistic story. Among adults with high amyloid levels, walkers taking 3,000 to 5,000 steps demonstrated a delay in cognitive decline of approximately three years. If the walker took 5,000 to 7,500 steps, the delay increased to approximately 7 years. Sedentary individuals experienced a faster rate of tau progression, a faster rate of memory loss, and poorer daily functioning.

Researchers utilized yearly cognitive assessments and sophisticated imaging to understand why being active appeared to be beneficial. Using statistical models, they found that almost all the benefit for cognition and memory was from the slower buildup of tau. In individuals with high amyloid, tau explained almost all of the relationship between being active and cognitive changes, and nearly half of the relationship between activity and daily living.

Being observational in nature, the project could not demonstrate that activity concurrently stops Alzheimer's disease. However, the researchers were able to test whether the early and undiagnosed disease may have contributed to some participants being less active. They found no evidence to support this hypothesis.

At the start of the study, there were no differences in activity level based on memory or levels of amyloid and tau. The findings were still solid even when removing participants in the first two years who later developed MCI.

Randomized trials can still be conducted to test whether activity can actually change the onset of Alzheimer's disease, but these findings, at least, make inactivity a suitable target for future prevention work.

The participants, aged 50-90, allowed researchers to measure change over a long period of aging. Many participants had not changed their routines for decades, which shows that step counts are a valid and stable marker of long-term habit changes. Over time, the data revealed a cohort of individuals who maintained their mental fortitude not through running marathons, but through a constant and steady degree of movement every single day.

For the scientists in the field, the findings present a potential tactic for future trials. Sedentary middle-aged adults with elevated amyloid may represent the ideal population for a study testing whether exercise has the potential to alter early tau development. Future trials could even explore combining activity-based programs with new amyloid-lowering agents to see if the combination of benefits yields greater outcomes.

"We are excited that data from the Harvard Aging Brain Study has aided the field in better understanding the role of physical activity for brain health," stated Reisa Sperling, MD, one of the leaders of the study. "The data indicates that it is possible to develop cognitive reserve in the context of pre-clinical Alzheimer's disease."

The next step for the research team is to understand the types of movement that matter most. They are interested in examining the intensity of activity, long-term patterns of behavior, and potential biological pathways that connect activity and tau.

For many people, the day-to-day message is simpler. Long-term brain health may be less about achieving the perfect goal and more about establishing a habit. "Every little bit matters," claimed Wai-Ying Wendy Yau, MD, the first author of the study. "Even small increases in daily activity can build up over time and result in meaningful change."

This research has real potential for meaningful cognitive health, as it implies that even incremental increases in daily movement, as defined in the study, may slow deleterious brain changes long before individuals experience symptoms of cognitive decline.

The findings may also inform future trials that would develop activity-based programs for individuals at early stages of risk for developing Alzheimer's disease, either alone or in combination with other treatments. It gives families and caregivers optimistic news that habitual activity can sustain memory and independence over the long term.

Research findings are available online in the journal Nature Medicine.

Like these kind of feel good stories? Get The Brighter Side of News' newsletter.