Exercise and the ageing brain

This article explores the impact of exercise on the aging brain—and affirms the message that ‘what is good for the body, is good for the brain’

by Terry Eckmann, PhD

Aging and brain health is a topic of great interest as the older-adult population continues to grow. In 1900, the average life expectancy was approximately 47 years, while today’s life expectancy is roughly 78.¹ It is estimated that women who now reach age 65 will have an average life expectancy of almost 85 and men who make it to 65 can expect to live to 82.¹ Longer life expectancy brings with it the need to maintain a healthy body and brain as the foundation for leading the fullest, most productive life possible.

Neuroscientists are gaining valuable information about the brain-body connection. In fact, we have learned more about the brain in the past 10 years than we did in the previous century. Dramatic new imaging techniques—Magnetic Resonance Imaging (MRI), Nuclear Magnetic Resonance Imaging (NMRI), Positron Emission Tomography (PET), and Single-Photon Emission Computed Tomography (SPECT)—allow researchers to study the workings of the human brain in action. This has opened a vast frontier of knowledge on cognition, memory and learning throughout life.

What neuroscientists have discovered in the past 5 years alone paints a riveting picture of the biological relationship between the body and the brain. The message is loud and clear! What is good for the body, is good for the brain. The “use it or lose it” principle refers to brain health, as well as to muscle and cardiovascular fitness. And according to Small,² Nussbaum,³ Ratey⁴ and Medina,⁵ exercise is one of the most important predictors of brain health through the life span.

Neuroscientists have shown that the brain stays “plastic,” or changeable, in later life. Neurons, or nerve cells, should remain alive and able to maintain and form new connections and networks in response to learning.6 What this means is, just as with muscle and cardiovascular health, the brain can change in response to exercise and other positive lifestyle choices at age 9 months or 90 years.

To begin to see how exercise can positively impact brain functioning throughout the aging process, it helps to have an understanding of the brain and how it works.

About the brain
There is no greater or more complex system than the human brain. This amazing connection of neurons weighs approximately 3–4 lbs. and is responsible for all of our thoughts, emotions and behaviors. About the size of 2 fists together with knuckles touching, the brain accounts for nearly 2% of the body’s weight, yet consumes approximately 20% of its oxygen and 20% of its glucose. In addition, this organ—which is comprised of 78% water, 10% fat and 8% protein—needs about 8–12 glasses of water a day and 8 gallons of blood an hour for optimal functioning.⁷

The brain has about 100 billion neurons that can connect many times to form synaptic connections. Each neuron has an electrical chemical response. The nucleus is where the neuron fires to begin the electrical chemical response, while the axon is the long arm of the neuron that carries electricity and chemicals to communicate to another nerve cell. Chemicals travel down the axon to the terminal where the chemicals jump across a space called the synapse and lock into the neuron’s dendritic receptors. Dendrites are the finger-like projections of the neuron. When we learn something new and when we exercise, we grow dendrites and dendritic branches, thereby increasing the brain’s ability to store and transmit information.⁸

As early as age 40, however, we start to lose approximately 5% of brain volume every decade of life.⁴ It is estimated that 50 million Americans suffer from diseases of the brain, according to the National Institute of Neurological Disorders and Stroke, one of the country’s National Institutes of Health.⁹ And in the United Kingdom, Alzheimer’s Disease International estimates that there are 35.6 million people living with dementia worldwide.¹⁰ Dementia is a brain disorder that seriously affects a person’s memory, thinking and reasoning skills. The most common form of dementia is Alzheimer’s disease.

In the United States, one in eight people ages 65 and older has Alzheimer’s disease, while the prevalence rises to nearly half of those ages 85 and beyond.¹¹ Women appear to be more susceptible. Approximately 16% of women ages 71 and older are believed to have Alzheimer’s or another form of dementia compared with 11% of men.¹¹

Usually, Alzheimer’s disease begins after age 65, but it is not a normal part of aging. Although age is one of the most important risk factors for Alzheimer’s, genetics plays a major role. Studies suggest that keeping the brain and body active may be among the most important ways to reduce risk and possibly prevent the disease.¹²

What happens to the aging brain without exercise?
Without exercise, the heart, lungs and muscles work less efficiently together. When that happens, the brain gets less of the blood, oxygen and glucose so vital to its functioning. Further, lack of physical activity is a risk factor for heart disease, diabetes, cancer, stroke, obesity and high blood pressure, which also have an effect on brain function.

How we age is determined both by genetics and lifestyle choices—approximately one-third of brain aging is genetics and two-thirds, lifestyle. Aging is a continuous process from birth, though. That means Alzheimer’s, like heart disease, doesn’t start at age 60 or 70, but early in life.

The mental and physical diseases we face in the aging process are directly tied to the cardiovascular and metabolic systems. For example, diabetes increases risk of dementia by 65% and high cholesterol increases this risk by 43%.⁴ As insulin levels drop throughout the aging process, glucose has a harder time getting into the body’s cells to fuel them, causing blood glucose levels to increase. This raises the risk for diabetes. High glucose levels also create waste products that damage blood vessels and increase risk for stroke and Alzheimer’s disease.

As we age, cells in the body gradually lose their ability to adapt to stress. Neurons in the brain are affected in much the same way. Synapses erode when neurons get worn down from cellular stress, eventually severing the connections between them. With this decreased activity, the dendrites physically shrink and wither. If the neuronal, dendritic and synaptic decay outpaces the new construction of connections, we begin to see problems with mental function. Cognitive decline and neurodegenerative diseases typically stem from dysfunctional and dying neurons. Exercise can make a difference, counteracting many of the effects that lead to the loss of brain function possible with the aging process.

Table 1. The effects of 30 minutes of moderate to vigorous aerobic activity

What happens to the aging brain when we exercise?
A great deal of research supports the positive impact of regular aerobic exercise on the aging brain.^{2,3,4,5,6,8,13} For example, one study of healthy adults ages 60–75 found that mental tasks involved in executive control—monitoring, scheduling, planning, inhibition and memory—improved in a group doing aerobic exercise, but not in a control group.¹⁴ Also, a longitudinal study of older Australian men¹⁵ concluded that 3 in 4 men who reach the age of 80 undergo successful mental-health aging; associated factors include education and lifestyle behaviors such as physical activity.

Regular exercise keeps the brain functioning optimally through the ways listed in the table on this page. The sections below discuss these effects in more detail.

Exercise changes the brain
Aerobic exercise increases brain-derived-neurotrophic-factor (BDNF), which is the most prominent in a family of proteins referred to loosely as neurotrophic factors. Neuroscientists have determined that BDNF has a fertilizer effect on the brain’s neurons and dendrites, helping them to grow and flourish. Tellingly, in 1990 there were a dozen papers on BDNF; now there are more than 5,500. Regular aerobic exercise increases insulin-like-growth factor (IGF-1) and vascular-endothelial-growth-factor (VEGF) as well, two proteins that build and maintain activity within the cell circuitry (the infrastructure of neuronal connections).

BDNF plays a significant role in neurogenesis, which is the process of stem cells dividing and developing into functional new nerve cells (neurons) in the brain. Studies have confirmed that neurogenesis occurs in the adult human, with the hippocampus being the major area for nerve cell growth. This area of the brain is associated with both long- and short-term memory and spatial orientation. While most studies on hippocampal neurogenesis have been conducted with rats,¹⁶ Eriksson and colleagues¹⁷ investigated whether neurogenesis occurs in the adult human brain, specifically the hippocampus. The researchers obtained human brain tissue postmortem from patients who had been treated with a chemical that identifies new neurons. Results indicated that the human hippocampus retains its ability to generate neurons throughout life.

So exercise both spawns neurons and stimulates an environment that enriches their growth and survival. Aerobic exercise also increases levels of important neurotransmitters, brain chemicals that transmit signals across synapses, to traffic in thoughts and emotions. Serotonin is the policeman of the brain, keeping brain activity under control. Norepinephrine amplifies signals that influence attention, perception, motivation and arousal. And dopamine is the learning, reward, attention and movement neurotransmitter. Most of the drugs used to improve mental health target one or more of these three brain chemicals.

In addition, regular aerobic exercise sends lots of oxygen-soaked blood to the brain to deliver glucose and oxygen while removing waste products that inhibit the process. Aerobic activity also improves the ability of both body and brain to use glucose to provide energy. (Remember, the brain uses 20% of the body’s energy.) By increasing receptors on muscle cells, aerobic exercise enhances the muscles’ ability to use glucose for energy; it also increases levels of IGF-1, which regulates insulin in the brain, thereby improving synaptic connections. High glucose levels negatively impact the brain by decreasing levels of BDNF. Regular exercise helps to keep glucose at an optimal level.

Of further note, brain volume grows with regular aerobic exercise due to an increase in capillaries, blood volume, nerve cell growth, and dendritic branching. Exercise increases blood flow by expanding the network of blood vessels in the brain while stabilizing existing “transportation structures.” This increased capillarization raises levels of oxygen and glucose in the brain.

According to Rogers et al.,¹⁸ recently retired adults who exercised had nearly the same level of blood flow in the brain after 4 years, while an inactive group saw a significant decrease. In addition, Kramer and colleagues¹⁹ compared adults ages 60–79 years who walked 3 times weekly at 40–70% maximal heart rate, to those who stretched an equal number of times per week. After 6 months, the walkers had improved their ability to take in, transport and use oxygen by 16% as measured by maximal oxygen consumption (VO₂ max) testing. They had also increased their brain volume in the frontal and temporal lobes, as evidenced by brain MRI scans.

Health and lifestyle: exercise is medicine What is good for the body, is good for the brain—and so is the opposite. People who are obese are twice as likely to suffer from dementia, and if we factor in high blood pressure and high cholesterol, conditions that often accompany obesity, the risk may actually be sixfold.⁴ Exercise plays a significant role in reducing obesity by burning calories, boosting energy levels, lowering stress, reducing appetite, elevating mood and increasing motivation.

Research indicates that stress also may be detrimental to brain health and memory performance.²⁰ When we feel stressed, our adrenal glands release a chemical called cortisol, and chronically high levels of cortisol lead to cell death in the hippocampus. Studies of Vietnam veterans in the US show that prolonged exposure to stress does adversely affect this area of the brain.²¹ Human investigations further indicate that several days of exposure to high cortisol levels can impair memory.²² Chronic stress can contribute to depression and anxiety disorders as well, which interfere with normal memory processing, especially as people age.²³ This suggests that learning to manage and minimize stress may have a beneficial impact on brain health.

Depression, too, is positively affected by regular exercise. In fact, an exercise training program may be considered an alternative to antidepressants for treatment of depression in older adults, according to Blumenthal et al.²⁴ In this study of 156 men and women over age 50 who were randomly assigned to a program of aerobic exercise, antidepressants or a combination thereof, exercise was equally as effective and more longlasting than antidepressants in decreasing depressive symptoms, even though these drugs may have facilitated a more rapid response to treatment.

Exercise is medicine. Choosing exercise regularly makes a difference in achieving a healthy body and brain.

What are the effects of exercise on dementia/Alzheimer’s?
The lifestyle choices that lead to obesity, diabetes, high cholesterol, high blood pressure and heart disease also increase risk for deterioration of brain health, as mentioned previously. Studies suggest that exercise can lower risk of dementia by 50–60%,⁵ and decrease Alzheimer’s risk by 60%.²⁵ Friedland and colleagues26 conducted a study with 500 participants that determined those who were physically active were 3 times less likely to get Alzheimer’s.

To some extent, exercise counteracts vascular damage. Stroke and Alzheimer’s patients who participate in aerobic exercise sometimes improve their scores on cognitive tests. It is suggested that because physical exercise increases cerebral blood flow (which in turn promotes neurogenesis), there is decreased risk of Alzheimer’s for those without the disease and regeneration of neurons for those experiencing it.^4,19

The best way to guard against neurodegenerative disease is to build a strong brain. Aerobic exercise accomplishes this by strengthening connections between brain cells, creating more synapses, developing neurons and increasing dendritic branches. Weuve et al.²⁷ studied 18,766 women ages 70–81 and found that those with the highest levels of energy expenditure had a 20% lower chance of being cognitively impaired on tests of memory and intelligence. The research indicated positive results even with modest levels of walking 90 minutes a week, and best results from 4 hours running or 12 hours walking per week.

Regular exercise further helps the brain by slowing the natural decline of the stress threshold with aging. The mild stress of exercise improves the ability to cope with more severe stress. It also reduces toxic levels of cortisol and increases levels of BDNF, particularly in the hippocampus.²⁸

If the brain isn’t actively growing, it is very likely dying. The good news is that beginning an exercise program at any age can benefit both brain and body. In a review of literature, Kramer et al.¹⁹ indicated that the benefits of physical exercise promote brain and cognitive vitality well into older adulthood. The body was designed to move; we know now that the more we move the body, the more we engage the brain. Through this brainbody connection, we can build and maintain a healthy body and brain with exercise—and lay the foundation for the most productive, full life possible at any age.

Terry Eckmann, PhD, is a professor at Minot State University (MSU) in North Dakota. Eckmann serves on the Advisory Board for the International Council on Active Aging®. She presents internationally and writes for a variety of publications on topics relating to exercise and aging. Eckmann has been recognized for her work, with awards including the North Dakota Association for Health, Physical Education, Recreation and Dance (NDAHPERD) University Honor Award and University Teacher of the Year Award, MSU Board of Regents Award for Research and Scholarship, IDEA Make Fitness Happen Award, and Industry Enhancement Award from Club Industry.

References

1. US Centers for Disease Control and Prevention, National Center for Health Statistics. (2011). Health, United States 2010: With Special Feature on Death and Dying. Table 22, p. 134. Hyattsville MD: US Government Printing Office. Retrieved on November 30, 2011, from http://www.cdc.gov/nchs/data/hus/hus10.pdf#022.
2. Small, G. (2006). The Longevity Bible: 8 Essential Strategies for Keeping Your Mind Sharp and Your Body Young. New York NY: Hyperion.
3. Nussbaum, P. (2006). Brain Health Across the Lifespan: From Research to Practice. Boston MA: Learning and the Brain Symposium.
4. Ratey, J. (2008). SPARK. New York NY: Little Brown and Company.
5. Medina, J. (2008). Brain Rules. Seattle WA: Pear Press.
6. Mahoney, D., & Restak, R. (1998). The Longevity Strategy: How to Live to 100 Using the Brain-Body Connection. New York NY: John Wiley & Sons.
7. Jensen, E. (1998). Teaching with the Brain in Mind. Alexandria VA: Association for Supervision and Curriculum Development.
8. Madigan, J. B. (2004). Thinking on Your Feet. Murphy TX: Action Based Learning.
9. US National Institutes of Health, National Institute of Neurological Disorders and Stroke. NINDS Overview. Retrieved on November 30, 2011, from http://www.ninds.nih.gov/about_ninds/ninds_overview.htm.
10. Alzheimer’s Disease International. Statistics. Retrieved on December 6, 2011, from http://www.alz.co.uk/research/statistics.
11. Alzheimer’s Association. 2011 Alzheimer’s Disease Facts and Figures. Retrieved on December 6, 2011, from http://www.alz.org/downloads/Facts_Figures_2011.pdf.
12. US National Institutes of Health (NIH) State-of-the-Science Conference Statement: Preventing Alzheimer’s Disease and Cognitive Decline. Retrieved on November 30, 2011, from http://consensus.nih.gov/2010/alzstatement.htm.
13. Verghese, J., et al. (2003). Leisure activities and the risk of dementia in the elderly. New England Journal of Medicine, 348(25), 2508–2516.
14. Kramer, A., et al. (2005). Fitness, aging and neurocognitive function. Neurobiology of Aging, 206(1), S124–S127.
15. Almeida, O. P., et al. (2006). Successful mental health aging: results from a longitudinal study of older Australian men. American Journal of Geriatric Psychiatry, 14(1), 27–35.
16. Cotman, C., et al. (2007). Exercise builds brain health: key roles of growth factor cascades and inflammation. Trends in Neuroscience, 30(9), 464–472.
17. Eriksson, P. S., et al. (1998). Neurogenesis in the adult human hippocampus. Nature Medicine, 4(11), 1313–1317.
18. Rogers, R. L., et al. (1990). After reaching retirement age physical activity sustains cerebral perfusion and cognition. Journal of the American Geriatrics Society, 38(2), 123–128.
19. Kramer, A. F., et al. (2006). Exercise, cognition, and the aging brain. Journal of Applied Physiology, 101(4), 1237–1242.
20. Small, G. W. (2002). Clinical Review: What we need to know about age related memory loss. BMJ, 324(7352), 1502–1505.
21. Sapolsky, R. M. (1999). Glucocorticoids, stress, and their adverse neurological effects: relevance to aging. Experimental Gerontology, 34(6), 721–732.
22. Newcomer, J. W., et al. (1999). Decreased memory performance in healthy humans induced by stress-level cortisol treatment. Archives of General Psychiatry, 56(6), 527–533.
23. LeDoux, J. (2002). Synaptic Self: How Our Brains Become Who We Are. New York NY: Viking.
24. Blumenthal, J. A., et al. (1999). Effects of exercise training on older patients with major depression. Archives of Internal Medicine, 159(19), 2349–2356.
25. Northrup, C. (2006). The Wisdom of Menopause: Creating Physical and Emotional Health and Healing During the Change. New York NY: Bantam Books.
26. Friedland, R. P., et al. (2001). Patients with Alzheimer’s disease have reduced activities in midlife compared with healthy control-group members. Proceedings of the National Academy of Sciences of the United States of America, 98(6), 3440–3445.
27. Weuve, J., et al. (2004). Physical activity, including walking, and cognitive function in older women. Journal of the American Medical Association, 292(12), 1454–1461.
28. Adlard, P., & Cotman, C. (2004). Voluntary exercise protects against stress-induced decreases in brain-derived neurotrophic factor protein expression. Neuroscience, 124(4), 985–992.

Additional reading

• Adlard, P., Perreau, V., & Cotman, C. (2003). The exercise-induced expression of BDNF within the hippocampus varies across life-span. Neurology of Aging, 26(4), 511–520
• Bugg, J., DeLosh, E., & Clegg, B. (2006). Physical activity moderates time-of-day differences in older adults’ working memory performance. Experimental Aging Research, 32(4), 431–446
• Gage, F. H. (2002). Neurogenesis in the adult brain. Journal of Neuroscience, 22(3), 612–613
• Hall, C. D., et al. (2001). The impact of aerobic activity on cognitive function in older adults: a new synthesis based on the concept of executive control. European Journal of Cognitive Psychology, 13(1–2), 279–300
• Small, G., et al. (2006). Effects of a 14-day healthy longevity lifestyle program on cognition and brain function. American Journal of Geriatric Psychiatry, 14(6), 538–545
• Turner, N. (2009). The Hormone Diet: A 3-Step Program to Help You Lose Weight, Gain Strength and Live Younger Longer. New York NY: Rodale Books

This article is provided courtesy of the International Council on Active Aging www.icaa.cc