How Being Fit Preserves Brain Blood Flow
This Week’s Research Highlight
Background
Age does not just ravage the body. It also takes a toll on the mind.
As people get older, they tend to experience decreased cognitive performance. A major factor involved with this decline is cerebral perfusion (blood flow to the brain).
All cognitive activity depends upon continuous and sufficient delivery of oxygen and glucose to your brain cells. Furthermore, the brain needs to be able to flexibly adjust blood flow to different regions of the brain during demanding cognitive tasks, a phenomenon called neurovascular coupling. In addition, cerebral blood flow helps remove metabolic waste products from the brain, preventing buildup of toxins.
As we get older, blood flow velocity to cerebral arteries tends to decrease. Greater arterial stiffness, accompanied by elevated cerebral pulsatility (forceful blood flow through inelastic vessels) reduces efficiency of blood flow and leads to damage to the delicate blood vessels supplying the brain. Over time, this leads to structural deficits in the brain, which can disrupt a constellation of cognitive functions like memory, planning, and processing speed.
For this reason, decreasing brain blood flow has been linked to accelerated cognitive decline, and people who have lower cerebral blood flow have been shown to be more likely to go on to develop dementia years later.
One thing that we know boosts blood flow throughout the body, including the brain, is physical activity. And this effect seems to add up over time. Greater volumes of exercise, as well as the resulting higher cardiorespiratory fitness, are associated with reduced rate of brain atrophy with age. Remarkably, more than 80% of all cortical regions can be structurally and functionally modified by physical activity.
Could some of the beneficial effects of regular exercise on the brain be explained by maintaining healthy blood flow to the brain?
Study
To investigate the relationship between aerobic fitness and cerebral blood flow, researchers in New Zealand recruited a total of 307 healthy non-smoking men, spanning a wide range of ages (18-79).
These men differed in one key respect — their exercise history.
Half of them were sedentary, meaning no regular physical activity. The other half engaged in vigorous aerobic exercise more than four times per week and competed in local races. The researchers recruited these men specifically for these lifelong activity patterns (or lack thereof), to see whether their contrasting lifestyles affected blood flow to the brain.
To gauge blood flow, the researchers measured cerebral blood flow velocity, which is the speed at which blood travels through the brain’s blood vessels, through transcranial Doppler ultrasound. Basically, they stick a transducer near the subject's temple, which transmits sound waves into the skull. Sound waves bounce harmlessly off red blood cells in the artery, and the device "listens" for the sound waves as they return. Kind of like using radar to check how fast blood is flowing through the artery.
For this purpose, the researchers zeroed in on the middle cerebral artery, which is ideal for measuring cerebral blood flow velocity since it supplies much of the cerebral cortex. It is also relatively easy to access non-invasively, since it runs close to the surface of the skull.
On a separate day, participants also performed incremental exercise to exhaustion via either treadmill or stationary cycle to calculate their cardiorespiratory fitness (VO2max).
Results
After analyzing the data, the researchers determined that two factors were statistically significant predictors of cerebral blood flow velocity: age and VO2max.
Age was associated with decreasing cerebral blood flow velocity, on the order of about 1% per year. Which largely lines up with prior research in this area.
However, higher VO2max was linked to increased cerebral blood flow velocity, independent of age. Indeed, the endurance trained men had consistently higher cerebral blood flow velocity, compared to their sedentary counterparts, and this was observed across the full age range.
The difference between sedentary and trained men was calculated at 17%, which equates to a 10-year drop in their middle cerebral artery blood flow velocity "age."
In other words, endurance-trained people retain a degree of cerebral blood flow of someone a decade younger than them.
Importantly, this benefit of physical training was found to be independent of both BMI and blood pressure.
Underlying Mechanisms
Why precisely does physical activity help preserve cerebral perfusion?
Well, this particular study wasn't designed to answer this question, but we can make an educated guess based on what we know about exercise physiology.
Aerobic training elicits a host of long-term adaptations that chronically enhance blood flow:
- Increased cardiac output
- The heart muscle itself undergoes remodeling, becoming stronger and able to pump blood more efficiently.
- This results in a greater amount of blood the heart pumps per minute.
- Since more blood is pumped with each heartbeat, the brain receives a steady supply of oxygenated blood and nutrients.
- Expansion of blood vessels
- Aerobic exercise promotes angiogenesis, or the formation of new blood vessels.
- Increased density of capillaries throughout brain tissue improves delivery of blood, ensuring that brain cells are able to function at their best.
- Improved vascular function
- Aerobic exercise improves the function of the endothelium, the layer of cells that line our blood vessels. Specifically, it enhances the ability of blood vessels to dilate via increased production of nitric oxide.
- Nitric oxide helps blood vessels relax and widen, which reduces vascular resistance and enables more blood to flow unencumbered to the brain.
- Better autonomic balance
- Aging is associated with greater sympathetic nervous system activity, which in turn contributes to vasoconstriction (narrowing of blood vessels), including those of the brain. Aerobic exercise, in contrast, leads to greater parasympathetic activity over time, which helps modulate the undue effects of age-related SNS overactivity.
Turning Back the Clock
A cross-sectional study looking at lifelong endurance athletes might be viewed (rightfully) with some skepticism.
However, intervention studies in older adults have shown increases in brain blood flow in response to an exercise program, which lends further support to these findings.
Even better, these trials suggest that exercise can potentially erase declines in cognition that have already developed.
For example, a trial conducted by Duke University Medical Center researchers found that performing aerobic exercise three times per week for six months led to improvements in cognitive tests which were the equivalent of reversing nine years of aging.
Similarly, when older adults were assigned to a supervised aerobic exercise program, their verbal fluency (meaning how fast they can mentally retrieve information) improved by 2.4%, an improvement tantamount to being five years younger. Increases in cognitive performance, notably, were linked to greater blood flow to the brain.
Prevention is ideal, of course, but it's never too late to start.
Random Trivia & Weird News
🥔 Potatoes became a staple food in Europe due to publicity stunts concocted by a French agronomist.
The potato was first brought to Europe by returning explorers, who discovered them in Peru in 1536. However, they were viewed with suspicion, and even deemed inedible for many years.
But in the eighteenth century, Antoine-Augustin Parmentier, agronomist and (surely) the all-time biggest potato fan, was utterly determined to shift public perception. He ultimately achieved this through several angles.
For instance, he conducted public tastings and banquets, attended by high-profile individuals like Benjamin Franklin, wherein every dish was composed of potatoes. To further associate the humble potato with the elite, he also secured the support of the royal family, getting King Louis XVI to agree to allow him to plant potatoes near Paris and even getting Marie Antoinette to wear potato flowers in her hair.
Finally, Parmentier engaged in some very clever baiting tactics to attract interest in potatoes among the general population. Most notably, he would have military guards posted around his potato fields during the day. This was intended to draw public curiosity and make the crop seem extraordinarily valuable. Then, he deliberately removed the sentries at night, which of course lured people to trespass and steal the potatoes for themselves. This spread the tubers across France, and eventually all across Europe, as an affordable and resilient source of nutrition.
Parmentier by François Dumont, in 1812
Podcasts We Loved This Week
- Katie Okamoto: Can we stop eating microplastics? Via The Wirecutter Show.
- Anurag Singh: Urolithin-A’s ability to optimize mitochondrial efficiency. Via STEM-Talk.
Products We Like
Polar Verity Sense
If you’re not keen on chest straps, this is a nice alternative. The Polar Verity Sense is a waterproof optical heart rate monitor that you can wear on your arm. It syncs wirelessly with apps, where it provides real-time data on heart rate and distance.
The device is lightweight, comfortable, and very accurate. It also has a tremendous battery life, up to around 30 hours per charge, so you only really need to put it on the charger every couple of weeks.
humanOS Catalog Feature of the Week
The How-to Guide to Polarized Training
Analysis of the training diaries of elite marathoners, including the great Eliud Kipchoge, has revealed a somewhat counterintuitive finding: Rather than run at a pace that mirrors their racing speed, they spend the vast majority (80% or more) of their training time running at a very easy intensity.
There are solid physiological reasons for this. For one thing, we know that training volume is the key driver of mitochondrial biogenesis. Accordingly, it makes sense to accumulate lots of hours running, but also to keep it at a low intensity so that you can recover efficiently. Over time, this will lead to central and peripheral adaptations that contribute to a higher VO2max.
In this reference sheet, we explain how intelligently manipulating volume and intensity can influence adaptations to endurance training, and help you apply this cutting-edge strategy to your own training.
Wishing you the best,
