International Business Department           Liu Bojia           October 25, 2023

  When it comes to exercise, we may immediately think of its benefits for muscle and metabolic function. But a study from the University of Copenhagen shows that consistent exercise can also help prevent the onset of Alzheimer's disease (AD). That's because during exercise, blood vessels contract and dilate faster and blood flow increases, and these changes help boost brain health by increasing blood flow in the brain and boosting the flow of cerebrospinal fluid.

  According to the research team's paper, which has been published in Nature Neuroscience, neurons in the brain store very few energy metabolites themselves, so they rely heavily on blood flow supplies of oxygen and glucose to maintain normal function. In fact, when blood flow in the brain exceeds the levels needed to obtain oxygen and metabolites, it causes other knock-on effects.

  For example, the periodic oscillations of neural activity during our daily sleep prompt a rapid increase in blood flow to the brain, and this functional process of congestion drives cerebrospinal fluid towards the ventricles. And the flushing of cerebrospinal fluid effectively carries away accumulated waste products from the brain and reduces damage to brain cells from toxic molecules.

  "The elasticity of blood vessels decreases with age, and when they are less able to contract and dilate, the flow of cerebrospinal fluid becomes weaker," said Dr Stephanie Holstein-Rønsbo, the study's first author, adding that this is one of the reasons why people are more likely to suffer from AD as they age.

  However, past studies have not done a good job of distinguishing vascular activity from neural activity when looking at it, so it's inconclusive whether the flow of cerebrospinal fluid is necessarily related to changes in blood flow.

  To address this query, the team specifically stimulated blood vessels in the brains of mice through optogenetic techniques, a process that does not affect neuronal activity. The results showed that cerebrospinal fluid flow in the brain increased significantly just by the enhanced vasodilation. At the same time, a number of tracer markers appeared more visibly in the brains of the experimental mice compared to the control group, suggesting that cerebrospinal fluid was flushed into the brain at a higher level.

  In the sensory cortex, vascular stimulation elevated the efficiency of lymphatic influx (glymphatic infux) and clearance, while the rate of cerebrospinal fluid influx in the stimulated cerebral hemispheres increased by a factor of 1.6. And the degree of dilation and constriction of the cerebral arteries showed a clear coupling directly to the flow rate of cerebrospinal fluid around the arteries. The study thus also established that it is vascular activity that drives the influx and exit of cerebrospinal fluid into and out of the brain.

  The authors note that natural vasodilation during sleep enhances the efficiency of cerebrospinal fluid cleansing, which is why a good night's sleep is important in preventing AD. Although different from the principles of sleep that produce congestion, exercise also causes vasodilation and increased blood flow.

  Consistent exercise over time, along with a good diet, maintains blood vessel elasticity, strengthens heart function, and ultimately allows cerebrospinal fluid to better carry waste away from the brain. By exercising in the moment, you are able to prevent AD years earlier.

  In addition to that study, several other papers had revealed that the same hormones that are present during exercise can be good for the brain. Back in 2012, a study in Nature found that mice produce a hormone called irisin after exercise, which increases energy expenditure and boosts metabolism.

  And a follow-up study in Neuron further revealed that irisin can also help reduce beta-amyloid accumulation while improving cognitive function in AD mice. This is another proof that exercise has a potential role in preventing AD.