If you needed another reason to get your daily steps in, science just handed you one. A new study shows that walking daily can reduce the risk of cognitive decline — especially among those with a genetic predisposition for Alzheimer’s disease. Almost 3,000 participants between the ages of 70 and 79 reported their daily walking habits over the course of 10 years, according to research that will be presented Tuesday at the annual Alzheimer’s Association International Conference. Those who reported maintaining or increasing their walking habits over the years showed greater improvements in processing speed and executive function. The benefits of walking were especially noticeable among those with a genetic predisposition for developing Alzheimer’s disease, according to the preprint, which has not been peer-reviewed or published in a professional journal. “We know sedentary behavior increases as you get older, and physical activity decreases,” said senior study author Dr. Cindy Barha, an assistant professor of kinesiology at the University of Calgary in Alberta. “So we recommend reducing your sedentary behavior by introducing small bouts of walking in between those times you have to be sitting down.” How does Alzheimer’s disease work? Alzheimer’s disease is a severe form of dementia thought to be caused by a buildup of harmful plaques in the brain that interfere with how the nerve cells communicate, eventually leading to their death, Barha said. As more nerve cells die, people with Alzheimer’s can develop progressive memory loss, confusion, personality changes and physical decline. Eventually, the disease can be fatal, and there is no known cure. Genetics are thought to play a major role in the disease. Specifically, genotypes called APOE affect the metabolism of plaque and other fats throughout the bloodstream. One specific kind, APOE4, is known to make it harder for the brain to clear the plaques and is linked to a higher risk of cognitive decline. About 15% to 25% of people have this version of the APOE gene, and the only way to find out is from a genetic test, according to data from the US National Institutes of Health. The mind-body connection Although the new study did not test a uniform walking regimen, Barha suggests walking multiple times daily to break up sedentary behavior and maintaining consistent walking habits year to year to prevent cognitive decline. “More research is really needed to determine how many steps that really takes, but more is definitely going to be better,” she said. “The next steps would be to actually try to figure out the minimum amount of walking for different subgroups, (such as) females versus males, APOE4 carriers versus non-carriers.” A 2022 study found that even people who walked about 3,800 steps per day at any speed cut their risk of dementia by 25%. What might be going on between the brain and the rest of the body? Experts have several theories. For one, regular exercise has been shown to help the body produce more of a protein called brain-derived neurotrophic factor, or BDNF, which is like fertilizer for your brain, helping it grow more cells and form new connections, Barha explained. “We’re thinking there’s proteins released from the muscle that travel to the brain and, either across the blood-brain barrier or at the blood-brain barrier, start a reaction that eventually leads to increases in BDNF within the brain,” she said. Another theory is that exercise reduces neuroinflammation, a common symptom of Alzheimer’s disease. The brain sends immune cells called microglia to attack plaque buildup, but this can backfire, explained Dr. Christiane Wrann, an associate professor of medicine at the Cardiovascular Research Center at Massachusetts General Hospital and Harvard Medical School. Chronic inflammation can lead microglia to begin attacking healthy brain cells as well, damaging the brain’s connections. “If you exercise, you actually strengthen the gene expression program that microglia need to function properly,” Wrann said. Does greater risk mean greater reward? The researchers were surprised to find that walking provided the greatest benefit to those with the APOE4 gene compared to those without it. To understand why this is, more research will be needed — but Barha has a theory. “Before the study started, we think APOE4 carriers had more room to grow in terms of cognition, since they may already have been experiencing some cognitive decline,” she said. “They also have more room to show improvement.” It’s possible that the study itself also motivated participants with APOE4 genes to walk more than they had been beforehand, slowing their rate of decline. “This is a very strong example (that) it’s never too late to start exercising,” Wrann said. “Every step counts, and it’s much better to do an exercise regimen that you actually like, that you can actually stick to.”
