THE BRAIN – MOVE IT OR LOSE IT
The brain is increasingly understood to be more closely related to a muscle than an organ. And, like all muscles, the brain needs movement and exercise to reach and maintain peak performance. In fact, evolutionary science suggests that the very reason humans developed a brain was to enable physical movement. Therefore, by moving less we’re effectively regressing to the point of becoming brainless.
Sitting in an office chair every day for hours on end quite literally shrinks the brain. On the other hand, exercise is like fertiliser for brain cells, helping boost your capacity for learning, memory, and problem-solving, while enhancing focus and attention. Exercise helps both mind and body stay limber as you age.
We’ve all seen spritely nonagenarians (individuals in their nineties) who are sharp as a tack compared to their sedentary peers. Cognitive decline may feel like an inevitable part of ageing, but scientific research now overwhelmingly shows that dementia is irrevocably linked to underactive lifestyles over the decades before we begin to fully lose our faculties. The good news is, exercise offers a significant opportunity to help even older brains reverse degenerative changes and promote learning and growth, thanks to neuroplasticity and neurogenesis.
Sedentary lifestyles are increasingly recognised around the world as being a major contributor to depression, anxiety, dementia, Alzheimer’s disease, attention deficit disorder, and numerous other psychiatric conditions. By 2050, more than 130 million people are expected to be living with Alzheimer’s disease (Alzheimer’s Disease International), which will have far-reaching residual effects on our healthcare system and society as a whole.
A good level of cardiovascular physical fitness during middle-age has been associated with close to a 90% reduction in dementia risk in later life, and is inextricably linked to a host of mental and physical benefits that can be enjoyed for years to come.
So, how exactly is movement such a boon for cognitive health? And what’s the best way to exercise to boost brainpower through exercise? Let’s dig into the science and see.
WHAT OUR BRAINS ARE ACTUALLY FOR
Descartes famously said, “I think, therefore I am.” However, when it comes to matters of the mind, the more apt statement might well be, “I move, therefore I think.”
Millions of years ago, most of the creatures on Earth did not have a central nervous system (CNS), let alone anything resembling the human brain. Over thousands of years, the need for movement – specifically adaptable and complex movements to help organisms evade danger and find nourishment – led to the development of the CNS and the brain.
Humans are movers first and foremost, and anthropological research shows that the first regions of the human brain to develop were those areas that control movement. Subsequent brain growth extended outwards from the motor cortex, further adding capacity that allowed us to better think, plan and predict. Thinking is the evolutionary internalisation of movement as the nerve cells that are stimulated when we move are the same as those needed for other, higher order cognitive functions. Put simply, if we weren’t movers, we wouldn’t be thinkers.
As recently as 10,000 years ago, we were hunter-gatherers covering somewhere between 10-14 miles a day. Now, most of us spend around 12 hours a day sitting and staring at screens. And we wonder why it is so hard to concentrate! Our brains are suffering because our behaviour is essentially sending the signal that we don’t need all that gray matter after all.
This idea is supported by research courtesy of the Semel Institute for Neuroscience and Human Behavior at the University of California Los Angeles (UCLA). Through magnetic resonance imaging (MRI), researchers were able to investigate the effects of sedentary behaviour on the brain in middle-aged and older adults currently living without dementia. The volunteers also underwent cognitive testing and were asked about their levels of physical activity and the average number of hours each day they spent sitting. The researchers found that the more hours people spent sitting each day, the thinner the tissue in their medial temporal lobe (MTL). This region of the brain includes an area called the hippocampus, which is largely responsible for storing and accessing memory. Essentially, prolonged periods of sitting during middle age can adversely affect the physical construction of the brain, which in turn negatively impacts our ability to process information. Sit for too long and the MTL becomes thin, even in people who try to offset sedentary behaviour with regular exercise. Conversely, physical movement enhances the thickness of the MTL and actively protects against memory loss and cognitive decline in older age, as well as results in improved cognitive performance at every stage of life (Siddarth et al., 2018).
One of the key findings in this study is that it’s not simply a lack of physical activity that raises the risk of early onset dementia and cognitive decline. Rather, sedentary behaviour is an independent risk factor for brain atrophy. Many people who are highly active – heading to the gym before or after work – are still sedentary for most of their day. This important detail helps explain why researchers may struggle to identify specific benefits of exercise interventions for cognitive health and emotional wellbeing. It’s not exercise alone that boosts brain health; it’s overall fitness and avoidance of an inactive lifestyle.
Why do movement and fitness matter so much when it comes to maintaining a healthy brain? Part of the answer lies within a range of chemicals including neurotransmitters and something called brain-derived neurotrophic factor (BDNF).
BDNF – THE BRAIN FERTILISER
In the 1990s neuroscience underwent a rapid period of discovery, uncovering exciting insights into how the brain can actually incite growth. Thanks to technology such as MRI and spectroscopy, as well as chemicals able to bind to BDNF, researchers could see for the first time that stem cells in the brain were forming new neurons (neurogenesis). This was remarkable, particularly given that the understanding within the scientific community up to this point was that, once a person lost brain cells after damage from a stroke, for instance, the skills and functions associated with that area of brain tissue had also been lost for good.
It was also widely accepted that brain development stops after childhood, and that, as adults we have to work with the finite gray matter we have and face inevitable atrophy and loss of brain cells as we age. We now know that stem cells stick around for our whole lives, allowing for the development of new brain cells and connections, thanks to biomechanisms involving brain-derived neurotrophic factor (BDNF), other neurotransmitters, and the right external stimuli. This effect is known as neuroplasticity – basically the potential to keep developing new neural pathways in response to our physical environment, including exercise – and neurogenesis – the process of growing new brain cells.
These revelations about the brain were industry game changers. If the brain could grow new cells and form new connections regardless of a person’s age or circumstances, there was significant hope for our ability to rewire the brain after injury and perhaps even reverse or prevent cognitive decline and dysfunction over time.
Further research found that, while lifelong learning boosts neuroplasticity and neurogenesis, nothing enhances these processes like living an active lifestyle with lots of movement throughout the day. Put simply, just as exercise is key to muscle growth, it is also vital for helping the brain grow stronger, more resilient, and more flexible. In the human brain, thousands of new neurons are added every day; unfortunately, most of these new cells don’t survive long, with more than half dying within weeks of development (Shors et al., 2012). The trick to keeping these neurons alive and well is to stimulate the cells through ongoing learning combined with a diverse set of physical activity.
Physical movement increases the number of stem cells in our brain tissue, creating a larger pool of new neurons (Blackmore et al., 2009). So, even if most new neurons continue to die shortly after being created, those who stay active have a higher number to start with and a higher number left over. And, by combining consistent exercise with intellectual activity, we retain more of these brain cells and enhance our overall brain capacity. This two-step process shows that it takes both continual exercise and a commitment to learning in order to become smarter. We’ll come back to this, but first let’s look more closely at the neurotrophic factors, including BDNF, that help spark neurogenesis and facilitate lifelong learning.
EXERCISE AND BDNF
Brain-derived neurotrophic factor (BDNF) was first discovered in 1989 by Yves-Alain Barde and Hans Thoenen while studying the brain tissue of pigs. BDNF is a neurotrophin, as well as a nerve growth factor (NGF), neurotrophin 3 (NT3), and neurotrophin 4 (NT4). Its most important functions include neuronal developmental, regulation of synaptogenesis, neuroprotection, and control of synapse activity influencing memory and cognition (Kowiański et al., 2018).
The brain releases BDNF in response to the increased mental demands associated with movement, which triggers brain cell growth and further release of BDNF. As BDNF floods the brain, it fundamentally changes the structure and function of brain tissue, making it easier to learn, consolidate information and skills, and to stay sharp, active, and motivated both physically and mentally. BDNF is at once both the fertiliser and the landscaper of the brain.
At the time of writing, there are over 1,300 published papers looking at the relationship between BDNF and exercise, including at least 50 clinical trials investigating the effects of physical activity on BDNF in human volunteers.
In a 2010 review of randomised controlled trials, Smith and colleagues looked at the effects of aerobic exercise on neurocognitive performance. They included 29 studies, involving over 2,000 volunteers, and conclusively found that exercise was associated with improvements in attention and processing speed, as well as executive function and memory. One study found that high impact, short exertion anaerobic running led to significant increases in BDNF and catecholamine (epinephrine, dopamine and norepinephrine) levels and enabled volunteers to learn new vocabulary 20% faster than volunteers who rested. (Winter et al., 2007). The results also showed that more sustained BDNF levels during learning following intense exercise seemed to facilitate better short-term learning, while dopamine was linked to improved immediate retention of new vocabulary, and epinephrine to our long-term memory.
Several studies looking at the neuroprotective effects of BDNF have involved people with multiple sclerosis (MS), a disease that leads to progressive loss of the insulating sheath around the nerves. In one study, BDNF levels were found to be 21% lower in people with MS, compared to healthy controls. After a 24-week exercise intervention, BDNF levels in the MS patients increased by an average of roughly 15%, whereas volunteers assigned to a sedentary control group had decreases in BDNF of around 10%. The exercise group, but not the sedentary group, also saw improvements in muscle strength, exercise tolerance, and body composition (Wens et al., 2016). A review of studies examining the effects of aerobic exercise on BDNF levels in people with neurodegenerative disorders like MS found that, while a large effect was seen with a regular exercise program, even a single bout of exercise had minimal effect, strongly suggesting that daily walking can be incredibly advantageous for people living with neurological disorders (Mackay et al., 2017).
The stark reality is that sedentary behaviour has fast and direct negative effects on neurogenesis, brain plasticity, neurotrophin (BDNF) production, angiogenesis, and control of inflammation and pathological processes that contribute to cognitive decline, anxiety, depression, and even neurodegenerative disease (Chastin et al., 2014).
HOW SEDENTARY BEHAVIOUR AFFECTS OUR ABILITY TO LEARN
The importance of movement in learning is now recognised by many health and education authorities worldwide. Among them includes the United States National Institute of Medicine, which recommends that fitness-based physical education should be a core school subject, not because of physical health, but because of its direct benefits for learning. In one school district, teachers took these early neuroscience findings to heart and implemented a fitness-based learning model that has had startling benefits.
In the Naperville school district in Illinois, students engage in a minimum of 40 minutes of active movement each day while at school. This doesn’t mean standing around idly on a football field or waiting for a pass on the basketball court. Instead, students take part in activities designed to get their heart rate up to 75-80% of their maximum, whatever that figure may be. The kids run, perform calisthenics, climb, dance, and participate in other pursuits every day. What’s more, guidance counsellors have begun to schedule the kids’ hardest subjects immediately following fitness classes so as to maximise their post-workout learning potential.
To back this up with data, in a country where a third of children were overweight in 2003, just 3% of Naperville kids were overweight the year after the implementation of this new system (Ratey, 2008). And, in the Trends in International Mathematics and Science Study (TIMSS) used to assess students’ knowledge across countries, Naperville kids (who competed as a country themselves) came in first in the world for science and sixth in the world for mathematics (Ratey, 2008). For comparison, the U.S. as a whole came in eighteenth and nineteenth in science and mathematics, respectively.
Seeing the success following the Naperville system, researchers have scrambled to determine the underlying factors that drive these positive changes in overall health and academic performance. Subsequent research, including the FITkids study, has found that daily exercise has significant benefits for executive control, accuracy, and reaction times in kids as young as seven (Hillman et al., 2014). Other studies have found that physical activity improves oxygen delivery to the brain, which in turn enhances bone and muscle strength in kids, and increases resistance to stress (Frischenschlager & Gosch, 2012).
Conversely, sedentary kids who engage more frequently in passive activities, such as watching TV or playing seated video games, have more difficulty with attention, focus, and behavioural issues compared to their active peers who demonstrate better reaction times and visual selective attention (Alesi et al., 2014; Syväoja et al., 2014). These studies, and others like them, overwhelmingly support a positive effect of physical fitness on academic achievement in school children (Castelli et al., 2007; Chomitz et al., 2009).
While studies about learning are most often applied to children or adolescents, there’s plenty of evidence supporting the cognitive usefulness of regular physical activity in adults, as well as the perils of too little.
In one study with older adults, a six-month program of daily brisk walking not only led to significant improvements in cardiorespiratory fitness, but also to improved executive function, including reasoning, working memory, and task-switching abilities (Baniqued et al., 2018).
The research investigating the relationship between physical fitness and cognitive function becomes a little more complex in adulthood, in part because adults tend to be better at compensating for reduced capacity in some cognitive tasks by calling on other skills (Kamijo et al., 2010). In addition, research suggests that it is not high intensity aerobic fitness that predicts cognitive health. Rather, an active versus a sedentary lifestyle seems to be a better predictor of robust cognitive function throughout the lifespan.
In one study, researchers found that higher levels of physical activity at the age of 36 was associated with a significantly slower rate of memory decline from ages 43-53, with further protective effects when physical activity continued during that time (Richards et al., 2003). In a large study involving 2,509 older adults, those who were more physically active were 31% more likely to maintain cognitive function over the following eight years compared to their more sedentary peers (Yaffe et al., 2009).
Just as it’s essential to build and maintain strong, healthy bones through load-bearing exercise, it’s also vital to exercise the brain to build new tissue and create new connections. The better one’s brain function at midlife, the more likely a person is to maintain cognitive health into his or her golden years. That said, even in cases where cognitive decline has become apparent, exercise has continually proven to help decelerate – and even reverse – cognitive impairment in older age.
SEDENTARY BEHAVIOUR AND THE RISK OF DEMENTIA
Every three seconds someone in the world develops dementia. A staggering 50 million people are currently thought to be living with dementia, a number that is expected to rise to an unprecedented 131.5 million by 2050. The global cost of dementia is estimated at more than a trillion U.S. dollars, including direct medical costs and the costs of informal and social care (Alzheimer’s Disease International). These figures do not take into account the cost associated with lost productivity, with the assumption that older adults are no longer in the workforce.
In many countries, retirement age has increased dramatically, meaning that dementia is ever more likely to strike while individuals are continuing to work for an income.
Most people now know that avoiding smoking, maintaining a healthy body weight, and staying intellectually and socially stimulated can help to stave off dementia. However, daily Sudokus will make little difference when an individual spends most of his or her day sitting.
A longitudinal study that followed the health of women for up to 44 years recently found that those with a high level of cardiovascular fitness in middle-age had an 88% reduced risk of dementia in later life compared to those who were only considered moderately fit. Up to 23% of the women in this study developed dementia over the 44-year period, but the highly-fit women who developed dementia did so an average of eleven years later than their sedentary peers (at 90 vs. 79 years old). After adjusting for body weight, the women with the lowest levels of fitness at age 44 had a significantly higher risk of dementia compared to women with medium fitness levels. Just 5% of the women in the highly-fit group developed dementia, compared to 25% of the medium-fitness group, 32% of the low-fitness group and a staggering 45% of those who were unable to finish the fitness test at age 44, respectively (Hörder et al., 2018).
Another analysis, looking at results from several studies concerned with the influence of fitness on dementia, came to a similar result. Adults over the age of 65 who were physically active had a 39% reduced risk of developing Alzheimer’s disease when compared to their non-active peers (Beckett et al., 2015).
One study of particular interest within the context of this book, looked at the hours spent sitting each day against the risk of poor mental health in later life. Compared to those who did not engage in leisure-time physical activity, active older adults had improved scores on emotional and mental wellbeing, as well as physical and social functioning, lowered bodily pain and heightened vitality. As found in many comparable studies, the number of hours spent sitting were inversely related with most of the scores used to assess quality of life (Balboa-Castillo et al., 2011).
The good news is that – just as you can always sabotage your health by sitting too much – it’s never too late to reap the benefits of exercise for one’s cognitive health. In fact, evidence strongly suggests that, even if an individual has poor fitness at age 44, switching sedentary behaviour for an active lifestyle can result in cognitive benefits later in life and a more healthy ageing process.
The benefits of exercise in preventing against Alzheimer’s disease (and dementia in general) shouldn’t be all that surprising given that the condition is associated with an excessive loss of neurons, particularly in the hippocampus and cerebral cortex. In autopsies of the parietal cortex of people with Alzheimer’s disease, researchers found a 3.4-fold decrease in the levels of BDNF microRNA, compared to controls without the condition (Holsinger et al., 2000). This decrease of BDNF in brain tissue is not only likely to contribute to dementia, but may also come as a result of dementia, given that people with Alzheimer’s disease are often more sedentary (both voluntarily and due to care practices) than their more active peers.
Maintaining physical activity and fitness in later life has also been found to help with emotional wellbeing. In one study, older adults who spent more time engaged in light physical activity, such as walking, scored higher on an Alzheimer’s quality of life test, which included better muscle strength and a significantly lower risk of depression (Arrieta et al., 2018).
MOVEMENT OVER MEDICATION FOR MENTAL HEALTH
The message is clear: people who are sedentary are almost twice as likely to be depressed as those who are physically active. According to a recent analysis of data from over 40,000 people, individuals under the age of 65 who sat for eight or more hours a day had a 94% increased risk of being depressed (Stubbs et al., 2018). With statistics such as these, it is hard to deny that we have a considerable amount of control when it comes to our mental and emotional state.
How is sitting linked to common mental health issues, such as depression and anxiety? Depression is now viewed by many physicians as being a consequence of the brain, i.e. through the loss of functional capacity as a result of decreased neurons and decelerated activity at the synapses. One recent study found that ceasing regular exercise directly increased depressive symptoms in healthy adults, particularly amongst women (Morgan et al., 2018).
Research linking exercise to improved mental health is nothing new. Studies began to investigate this idea back in the late 1970s, with significant work carried out at Duke University. As part of a long history of cardiac rehabilitation studies, researchers looked at the effects of A) exercise (in the form of treadmill walking or jogging) as treatment for people with depression and coronary heart disease, comparing it to B) treatment in the form of a placebo, C) treatment with the antidepressant sertraline (Zoloft), and D) a combination of Zoloft and exercise. After 16 weeks, exercise and Zoloft were found to be equally effective in reducing depressive symptoms, with a significantly greater effect compared to placebo treatment. Exercise had the added benefit of improving a measure of heart function (Blumenthal et al., 2012).
Early research found that patients who engaged in a walking program for cardiac rehabilitation tended to become less stressed, less aggressive, and happier, as well as more physically fit. In one early study in this field, Blumenthal and colleagues recruited healthy middle-aged volunteers and assessed the effects of continued sedentary behaviour versus a ten-week walking/jogging program on mental health. They found that almost everyone in the exercise group had improvements in their respective anxiety levels, decreased tension, depression, and fatigue, and more vigor than those who remained sedentary (Blumenthal et al., 1982).
Walking has also demonstrated a range of mood benefits in people living with a variety of chronic diseases and conditions. In a study of individuals being treated with chemotherapy for breast cancer, a 12-week, home-based, self-paced walking program was seen to have improvements in fatigue, mood, and self-esteem (Gokal et al., 2016). A similar program was associated with improvements in perceived stress and depression symptoms in people who had suffered a traumatic brain injury (TBI) (Bellon et al., 2015).
There’s no shortage of studies that exalt the benefits of walking to suppress depression. One study found that, in postmenopausal women with depression, a six-month moderate intensity walking intervention (three times a week, 40 minutes per session) led to significant improvements in depression compared to a control group assigned to a wait list (Bernard et al., 2015).
Given all we know about the benefits of exercise for the brain, the idea that movement can also benefit our psychological health isn’t all that surprising. The same mechanisms that support cognitive functioning also support emotional functioning; this includes improved dopamine receptivity and activity, neurogenesis and neuroplasticity, and better all-round metabolism in brain tissue due to improved circulation and nutrient uptake (Schoenfeld & Cameron, 2015).
BDNF plays a major role in brain function and has been implicated in the pathology of depression. People with depression are consistently found to have low levels of BDNF; given this known connection, it should come as no surprise that researchers have sought to harness its power and use BDNF within antidepressants. (Polyakova et al., 2015). So far, however, this has yet to be achieved in any meaningful way.
Between the brain and body is an effective feedback loop, whereby we create more BDNF when we use brain cells. And, as we already know, nothing increases BDNF like exercise, not even meditation or learning. We use more brain cells during physical activity than any other, leading to a flood of BDNF that promotes neuroplasticity, and dopamine and serotonin activity.
Improving neuroplasticity may, in theory, be particularly helpful for those who experience a certain kind of circular thinking typically seen in depression and other mental ailments. By enhancing the brain’s ability to form new connections and to effectively rewire itself, people may be better able to break free from their well-trodden negative thought patterns. This idea was borne out of research showing that exercise improves the response to cognitive behavioural therapy and medication in the treatment of depression (Gourgouvelis et al., 2018). Astonishingly, in one small study, an eight-week exercise intervention led to a therapeutic response (or, in some, complete remission) of depression symptoms in 75% of patients, compared to just 25% of those engaging solely in cognitive behavioural therapy with medication. Exercise also improved the participants’ sleep quality and cognitive function, and increased their BDNF levels in tandem with decreased symptoms of depression. With research upon research demonstrating similar findings, it’s surprising that physical exercise isn’t seen more often as part of the ‘doctor’s orders.’
Recent research in mice has found that BDNF levels correspond with novelty-seeking exploratory behaviour, suggesting that BDNF not only supports motivation but may also act as a comfort during new experiences. Indeed, administering BDNF to mice with an avoidant or balanced disposition was shown to increase exploratory behaviour (Laricchiuta et al., 2018). This may mean that by engaging in regular exercise and avoiding sedentary behaviour, humans who typically feel anxious in new situations may begin to feel more adventurous and comfortable with novel experiences.
Put simply, BDNF manipulation through the avoidance of sedentary behaviour offers significant opportunity for individuals to overcome their reluctance to exercise, and provides benefits for the mind, body, and overall health and happiness. In study after study, researchers have confirmed the benefits of movement – especially walking – for managing anxiety, depression, attention deficit disorder, obsessive-compulsive disorder, and even addictions, schizophrenia, and bipolar disorder. In many ways, movement is more effective than medication for treating and preventing mental health problems, and with far less consequences! In 2010, the American Psychiatric Association recognised for the first time that exercise is a proven treatment for depression.
Medications and psychotherapy can be expensive, inaccessible, have side effects, and be of limited use for many individuals. Not to mention the stigma that continues to surround mental health in many communities. Considering how depression and other mental health issues often have an underlying metabolic component, it makes intuitive sense to prescribe physical activity to combat depression and support ongoing mental health.
GIVE UP YOUR CHAIR TO BETTER MANAGE STRESS
How can exercise help improve our ability to resist the negative effects of stress? Part of the answer is through neurogenesis, specifically new growth of neurons and reorganisation of neurons mediated by the inhibitory neurotransmitter gamma amino butyric acid (GABA). This neurotransmitter has the ability to constrain excitatory neurotransmitter activity and slow our innate fight or flight response (Ma, 2008; Sah et al., 2017). In animal studies, rats who spent more time engaged in physical activity had higher GABA levels in key brain areas and were less vulnerable to the effects of stress (Molteni et al., 2002). Put simply, the fitter you are, the more stress you can effectively manage. When stress is particularly high, it activates the sympathetic nervous system, affecting the hippocampus, which is both the memory centre and the area of the brain that predominantly controls anxiety and panic.
There’s a reason why hot-headed people are told to ‘take a walk’ to cool off. An acute bout of exercise is like taking a bit of both Prozac and Ritalin; it effectively calms anxiety levels and cheers us up while allowing us to direct our focus to the situation at hand. Exercise increases norepinephrine, serotonin, and dopamine, which modulate the entire range of neurorunctional systems such as attention, aggression, motivation, concentration, alertness, memory, anxiety, irritability, mood, reward, and pleasure. And, of course, exercise increases BDNF, the brain’s fertiliser.
Most people have heard of a ‘runner’s high,’ usually attributed to endorphins released during exercise. What many people don’t realise, however, is that we also create our own marijuana-like neurohormones, called endocannabinoids, which are released when we experience injury. These endocannabinoids effectively calm the brain and help us feel happy and comforted. In tests with mice, endocannabinoids increased with voluntary physical activity (such as running) and have been associated with decreased anxiety, pain sensitivity, and sedation, effectively recreating a runner’s high in the animals; mice given a substance that blocks the effects of endocannabinoids did not experience these positive effects with exercise (Fuss et al., 2015).
About the Author
Eric Soehngen, M.D., Ph.D. is a German physician and specialist in Internal Medicine. With his company Walkolution, he battles the negative health effects that sitting has on the human body. Walkolution develops ergonomically optimized treadmill desks, which help to bring more movement into the daily work routine in the office or home office.
Photo credit: Alina Grubnyak