The Revolutionary New Science of Exercise and the Brain
John J. Ratey
Despite Hollywood’s protestations to the contrary the American way of life, and all those who follow it, seem to be failing. The obesity rate stands at 65% and is spiraling out of control. Over 10% of the population now has Type 2 diabetes, a fully preventable disease, which is implicated in further health problems such as heart disease. The leading cause of disability in the United States and Canada is depression, ahead of coronary heart disease and cancer. Those who do reach old age look forward to high blood pressure, diabetes, a failing family life, and yet more obesity. Over 13 million have a diagnosis of ADHD, with millions more suffering from nondiagnosed attention problems. Clinical anxiety is present in around 18% of Americans, manifesting as panic disorders, phobias, and social dysfunction. In international league tables measuring performance in literacy, math, and science, the United States has slipped out of the top twenty, below Cyprus and Slovenia. To combat this intellectual decline, schools are allocating more time to testing. It doesn’t work. The country rated the highest in literacy and math is Finland, in which there is no formal testing at school. In addition to extra testing, successive governments and school boards have pushed more lessons in math, science, and English, increasingly at a younger age, and at the expense of subjects seen as not academic. This doesn’t seem to be working either. Cutting physical education or gym class has not improved academic performance, and all the evidence suggests that children who are not engaged in physical activity are less intelligent, while adults who do not exercise are more likely to suffer from a myriad of diseases, both physical and mental. The reason for this is to be found in the relationship between exercise, the body, and the brain.
There are three main types of stress: social stress, physical stress, and metabolic stress. It can be acute, or, as life’s challenges become insurmountable, stress can become chronic. During a period of chronic stress, emotional strain becomes physical strain, which soon takes its toll upon the body. Anxiety, depression, heart problems, high blood pressure can all occur, while cancer looms large. The relentless barrage of chronic stress eventually starts to tear at the very architecture of the brain, forcing it to get locked into a pattern of negative thought. The brain systems that are negatively affected during chronic stress are those that manage energy, attention, and memory, and the hormone that reeks the most havoc upon both body and brain is cortisol, to which our attention now turns.
During times of stress, epinephrine converts glycogen and fatty acids into glucose. Cortisol starts to enter the bloodstream, signaling to the liver to make more glucose available. At the same time, cortisol blocks insulin receptors at nonessential tissues and organs, to ensure enough glucose reaches the brain. Protein is converted to glycogen, and the process of storing fat commences, especially fat around the belly. After a period of acute stress, or during a long haul of chronic stress, the body calls for more glucose, so a person craves, then reaches for, simple carbs and sugars that will very quickly fuel obesity. Obesity causes a range of well-documented problems, but chronic stress coupled with excess cortisol causes additional problems. It damages blood vessels, and allows plaque to build up, resulting in atherosclerosis. As glucose levels are raised, chronic stress is implicated in diabetes, which in turn is associated with numerous serious health problems. Finally, excess cortisol dampens the immune system, leaving the body prone to a multitude of diseases including autoimmune illnesses, arthritis, chronic fatigue, and not least cancer.
Chronic stress does not just attack the body. It also attacks the brain. In the brain, cortisol switches on genes inside cells that make the proteins used as building material for cells, dendrites, receptors, and bulkier synapses. At first glance this might seem to be a good thing as bulkier synapses should mean better memory, but the only type of memory strengthened is survival memory. If a new memory comes along during chronic stress it is not able to recruit neurons to make its own circuit. It is blocked. With continually raised levels of cortisol learning new memories is very difficult, and existing memories cannot be recalled.
To summarize, chronic stress is not a joke, it is associated with all of the major debilitating and killer diseases of our time, while also enfeebling the mind. One of the great paradoxes of our current time is that there is not more hardship, only news of it, lots of news of it, which is dumped on us twenty-four hours a day by various technological means. It is a torrent of tragedy, fear, and warmongering. Avoiding this ever-present deluge is one way to avoid stress. Having more friends, with a good support network, and frequent contact is another. However, the principal means for avoiding and curing chronic stress is exercise.
Regular aerobic exercise is the best form of exercise for chronic stress and for lowering cortisol. This form of exercise calms the body making it more resilient. It produces more insulin receptors to make better use of blood glucose caused by excess cortisol, and increases IGF-1 used by insulin to manage glucose levels effectively. The neurotrophin BDNF is increased, which further keeps cortisol in check and raises other neurotransmitters, enabling thought and memory. Exercise also produces FGF-2 and VEGF, which build new capillaries and expand the brain’s vascular system. All of these factors are brought about by aerobic exercise, and all combine to strengthen the body and the brain, stopping the damaging effects of chronic stress from taking hold.
Anxiety is the body’s response to stress. When a person worries to the point that they cannot function normally, even when there is no real threat, this is an anxiety disorder. The constant worry continues until all perspective is lost, and clear, rational thought is near impossible, replaced by irrational dread. Anxiety does not just harm the mind. There are physical symptoms too, which include feeling tense and jittery, or sweating and having a racing heart twinned with severe chest pains. These chest pains may not necessarily be benign. The standard approach to treat anxiety has been to prescribe drugs. In the short term this is not a bad approach, as it often gives quick relief. A article published in the New England Journal of Medicine in 2004 reviewed all treatments for generalized anxiety disorder, then listed thirteen pharmaceutical drugs proven to work, though all with formidable side effects. The problem with this review, as correspondents were quick to point out, was that it only looked at drug treatment for anxiety; no other remedies were considered. Cardiologists have noted for a number of years that anxiety is a risk factor for various heart problems. The cure, in their view, is exercise, which reduces the risk of heart disease, and also cuts anxiety by half. Many peer-reviewed studies have been published on the benefits of exercise upon heart disease and anxiety, yet none were considered by the New England Journal of Medicine.
In the same year that article was published, researchers at the University of Southern Mississippi studied sedentary college students diagnosed with generalized anxiety disorder, in order to see the effect of exercise upon anxiety. The students were split into two groups, each told to do six sessions of twenty minutes of exercise over a two week period. The only difference between the two groups was in the type of exercise. The first group ran on a treadmill at 60–90% of their maximum heart rate, while the other group walked at 50% of their maximum heart rate. At the end of two weeks, levels of anxiety had reduced regardless of regime, but the participants in the more rigorous exercise program ended with lower levels of anxiety, and these levels fell more quickly. Further studies in other clinical settings also showed that aerobic exercise significantly lessened feelings of anxiety.
It did not take long for researchers to discover that three important neurotransmitters, which play a role in anxiety, are released during exercise. During exercise the essential amino acid tryptophan increased in the bloodstream. This amino acid is able to push through the blood–brain barrier increasing serotonin in the brain. Together the two chemicals calm us and enhance our sense of safety. The third chemical released while exercising is gamma-aminobutyric acid or GABA, a major inhibitory transmitter, which not coincidently is the primary target for numerous antianxiety drugs. Normal levels of GABA are important as they interrupt the obsessive feedback loop within the brain. In short, exercise increases GABA, which stops obsessive worrying; tryptophan and serotonin are released, which makes us feel calm.
In addition to these neurotransmitters, a molecule found in the heart called ANP is secreted by heart muscles when exercising. The molecule is of interest because it influences emotion. Once freed, it also crosses the blood–brain barrier, attaching to receptors in the hypothalamus, where it has a calming effect upon the mind. A further study found that injections of ANP into human volunteers reduced panic attacks. While antianxiety neurotransmitters are released in greater quantities during rigorous exercise, the calming molecule ANP is increased simply by walking thirty minutes a day. People who do so have lower levels of anxiety. Walking coupled with a burst of rigorous exercise reduces worrying thoughts even more.
Exercising to alleviate and fortify against anxiety is important for another reason: it distracts the mind from worrying. Many people who suffer from anxiety passively indulge their negative thoughts. They feel too helpless to change that which worries them. When these negative thoughts are indulged they become stronger and more difficult to remove. They take hold of a person, and debilitating anguish and negativity soon ensues. Even people not diagnosed with anxiety, or anything close to clinical anxiety, should pay little heed to negative thoughts or worries, lest they route new mental pathways through the brain, and become permanent. By making a conscious decision to act differently in the face of negative thoughts, we shift the flow of information in the brain, physically forging new pathways, which negate anxious feelings.
Exercise is superb at diverting our attention away from the rut of negativity. It provides distraction as the mind cannot process higher thought during rigorous exercise. It reduces resting muscle tension. It builds important neurotransmitters, improves reliance, and helps to reroute brain circuits, enabling the anxious person to break free of passively waiting and worrying.
According to the World Health Organization, depression is the leading cause of disability in the United States and Canada. It is not unreasonable to think that other English-speaking nations might be similarly affected. At any given time, almost 20% of Americans are suffering from depression, with a suicide every seventeen minutes. Almost three-quarters of those with depression also have another disorder including anxiety, substance abuse, and dementia. Depression, as with stress and anxiety, physically alters the brain. MRI scans of chronically depressed patients reveal structural damage in the parts of the brain associated with thinking. The scans showed that gray matter—the part of the brain that directs attention, emotion, and memory—was physically shrunken. Later scans with MRI and PET scanners showed a physical alteration in the brain’s emotional circuitry. The synapses lacked good connections, weakening the transmission of neurotransmitters such as serotonin. We know that for many people who suffer from depression, the brain is physically altered, and communication between neurons is impeded by poor connectivity. We also know, thanks to several important studies, that exercise prevents, treats, and can send depression into complete remission.
In 1999 at Duke University a sixteen-week trial of exercise versus the antidepressant sertraline (Zoloft) commenced. Three groups of volunteers were assigned either exercise only, Zoloft only, or exercise and Zoloft combined. The exercise comprised working out at 70–85% of maximum heart rate for thirty minutes, three times a week. At the end of the study all three groups reported a drop in depression, and 50% of each group were in remission. The conclusion was that exercise is at least as effective as an antidepressant for treating depression. However, six months later a follow-up showed that exercise worked better than antidepressants in the long term. Of those in the exercise group who had experienced a remission just 8% had relapsed back into depression, compared with 38% in the antidepressant group. From this and other studies, researchers have been able to determine a dose of exercise to be prescribed to those suffering from depression. For a 50% reduction in depressive symptoms, a person should burn 8 calories per lb. of body weight per week. Thus someone weighing 158 lb. would need to burn 1,264 calories a week during dedicated exercise sessions. But it’s not just clinically depressed people who might benefit from a dose of exercise. Exercise also prevents depression and makes well people feel more well. In 2006, a huge Dutch study of 19,288 twins and their families concluded that people who exercise are less anxious, less depressed, less neurotic, and more socially outgoing.
One word of caution is necessary. Exercise and medicine are not independent of each other. In the immediate term, drugs often work quicker, while exercise facilitates long-term change. Both treatments may be utilized for stress, anxiety, and depression.
As we age our cells lose their ability to adapt to stress. There is a lower threshold for fighting the molecular stresses of free radicals, excessive energy demands, and environmental stressors. The genes responsible for producing proteins that clear up damaging cellular waste stop doing their job. As damage builds up, the immune system sends in white blood cells to mop up dead cells, but this causes inflammation. This can create even more damaging proteins, and it is these proteins that are directly linked to Alzheimer’s disease. Women are especially vulnerable to this disease, as they are to dementia.
In the aging brain, neurons are worn down by cellular stresses, synapses are eroded, and dendrites physically whither. If this decay outpaces new construction, then neurodegenerative diseases set in, which are very tough indeed. Furthermore, capillaries shrink back restricting much-needed blood flow to the brain. Diseases of the body are also more prevalent. Around two-thirds of elderly people are overweight, 20% have diabetes, while heart disease, cancer, and stroke account for over 60% of all deaths. The average elderly person suffers from three chronic diseases and takes five prescription medications. There is a correlation between these diseases of the aging body and those of the mind. If you are obese you are twice as likely to get dementia; if you have diabetes there is a 65% higher risk of dementia; if you have heart disease you are more likely to fall victim to Alzheimer’s disease; if you have raised glucose levels, but are not diabetic you are 77% more likely to get Alzheimer’s disease. Conversely, if you reduce the risk of diabetes and cardiovascular disease, you are much less likely to have neurodegenerative diseases in old age.
Exercise is especially valuable for protecting the body and mind from the ravages of old age. In strengthening the cardiovascular system, exercise reduces blood pressure, meaning there is less strain on blood vessels. Contracting muscles when lifting weights strengthens the inner lining of blood vessels. Exercise also helps to expand the vascular network, creating circulation routes that protect against blockages. Nitric oxide is introduced, widening blood vessels, reducing the threat from clots, and boosting blood volume. Glucose and insulin are regulated negating the tyranny of diabetes. Mood is lifted, reducing the risk of dementia. And, importantly, the immune system is bolstered, which rallies T-cells to attack bacterial and viral infections, making the body more alert to the ever-lurking danger of cancer. Exercise that includes weight-lifting protects against the plunder of aging, giving us a fighting chance against the possibility of spending the last thirty bleak years of our life crawling on the floor, barely able to walk, unable to remember even the names of our family.
We now know the havoc that is reaped upon our body and brain if we fail to exercise. The question remains, what type of exercise. In simple terms any form of exercise, even walking, or perhaps especially walking, is protective and beneficial. A simple program of a traditional diet coupled with reduced intake of food, the avoidance of sugar, walking thirty minutes per day, and lifting weights in your own home two or three times a week, and doing ten minutes of Tabata three times a week will give huge health gains, protect against disease, and improve one’s mental state. At this point it is worth reiterating that women should lift heavy weights. You will not get bigger, nor become manly, but you will become stronger, leaner, and have a better metabolism. Squats, dead-lifts, bench and military presses, pull-ups, push-ups, the big compound exercises that work multiple muscle groups should be given preference.
The very best and most protective exercise program is 45–60 minutes six times a week, comprising the following:
1. Aerobic activity at 65–75% of maximum heart rate. During this type of exercise growth factors make more blood vessels and capillaries, and broken bits of DNA and inflammation factors are removed.
2. More strenuous activity at 75–90% of maximum heart rate. This should be done for five to ten minutes at a time within the workout, and might include running or hard cycling. At 90% or above of maximum heart it is near impossible to exercise for more than 30–60 seconds, yet this short period of time is extremely beneficial. Above 90% of maximum heart rate the pituitary gland in the brain unleashes human growth hormone (HGH), which burns belly fat, pumps up brain volume, and layers on muscle fibre. It also enhances our metabolic rate and balances neurotransmitters. A person need only go above 90% of maximum heart rate during one exercise session a week, and then only two or three times for 30–60 seconds. The best type of exercise for this is sprinting, either by running or on a bike. A word of caution: the obese, those older than forty, and those who have not exercised regularly for some time should not attempt this very high-intensity exercise until they have a foundation of six months of aerobic fitness.
3. Weight-lifting two or three times a week. This reverses aspects of aging at the genetic level. In one study, the genes responsible for brain growth acted as if they were thirty years old, rather than sixty-five. Researchers at Boston University found that a three-month, weight-lifting program resulted in 40% better muscle strength, lower anxiety, improved mood, and better confidence. Just doing squats with heavy weights doubles HGH when compared to running at high intensity for thirty minutes.
The biggest cultural paradigm shift of the late twentieth century has been the rampant spread and use of the internet. The information, the news, opinion, updated blogs, Twitter feeds, email interruptions, and a plethora of distractions vie for and challenge our attention. With continued and prolonged use of this medium, or access to it via the phone in our pocket, we expect things to happen immediately. We often do not plan, nor have patience, think things through, nor evaluate consequences. As exercise requires time, planning, and consistent long-term work in order to reap the benefits, it is often not given its due, or people feel they do not have the time. Just replacing nonessential time spent on the internet, time spent on keeping up with the news, or sending another frivolous email, with rigorous exercise would probably result in significant gains for many. Busy young mothers should walk with a stroller for thirty minutes a day, and attempt to lift some weights at home three times a week when things have quietened in the evening, just for 10–15 minutes per session.
As time passes on, and the exercises remain constant, they become easier to perform and more enjoyable to undertake. Anxiety levels decrease, life’s worries drift away, the black gloom of depression lifts, and stress evaporates. Thinking becomes sharper and memories are easier to store and retrieve. Physically we improve, we have more energy, better muscle tone, more strength, and a lean, hard, wiry body. As we then age we can continue to live life not needing assistance, protected against cruel, unrelenting neurodegenerative diseases. This can only happen if we exercise regularly and continually without slackening. Diet might be the Queen of Health, but exercise is the King. It is necessary and essential.