It’s no real surprise that an active lifestyle is beneficial for people with Alzheimer’s disease. But researchers from the University of California have now added another piece to the puzzle in understanding how physical activity improves brain health and helps people with Alzheimer’s disease.

According to their study, published earlier this week in JNeurosci, exercise might play a role in decreasing immune cell activation.

The brain’s immune cells, called microglia, activate to clear debris and foreign invaders from the brain. But too much activation can trigger inflammation, damage neurons, and disrupt brain signalling.

Animal studies have shown that increasing physical activity reduces abnormal microglia activation, but the link has not been established in humans.

The researchers tracked the physical activity of 167 people, 60% of whom had Alzheimer’s disease, for almost a decade. The participants wore activity monitors 24 hours a day for up to 10 days straight before annual cognitive exams.

They then analysed participants’ brains after their deaths, which occurred at an average of 90 years of age. After adjusting for age, sex, education, and motor performances, the researchers observed that brain immune cells were less active in those who exercised more, particularly in areas of the brain linked to Alzheimer’s disease.

“We’ve known for a long time that midlife physical activity is associated with a reduced risk of dementia,” says Professor Amy Brodtmann, a neurologist at the Florey Institute of Neuroscience and Mental Health in Melbourne, who was not involved in the study. “But how late-life physical activity improves brain health still isn’t clear.”

Brodtmann says past studies have looked at the effect of exercising on beta-amyloid and tau, two proteins that accumulate in the brain forming plaques and disrupting brain functioning. Muscle mass has also been associated with better brain health, while reducing cardiovascular disease and the risk of stroke in the brain through exercising contributes to lowering the risk of dementia.

The role of brain immune cells in cognitive decline is now receiving an enormous amount of attention. “We used to think that inflammation came after the pathologies in the brain,” Brodtmann said. “But what we’re now thinking is that other events in life, particularly vascular disease, can cause increased inflammation in the brain, and this may be the primary driver of the pathology [in the brain].”

Brodtmann says this study uncovered the positive effect of physical activity on neuroimmune modulation. “That means that at any stage in your life, you can affect your brain’s health by exercising.”

She says that physicians should encourage patients to exercise regularly, as well as adopt a Mediterranean diet and address all other risk factors.

“Age in itself is not a barrier to exercise,” Brodtmann says, adding that including physical activity in your routine could be as simple as going for a brisk, 30-minute walk most days of the week. Running, swimming, cycling and some gentle strength workout is also highly recommended.

As people get older, reduced mobility might be a challenge, but Brodtmann said some level of physical activity is beneficial at any age and stage of the disease.

“These diseases are usually the cumulative effects of a lifetime of not exercising or eating well, and this behaviour is not very easy to change.”

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