March 2010 Issue

Think Exercise for Brain Health
By Diane Welland, MS, RD
Today’s Dietitian
Vol. 12 No. 3 P. 24

Research linking fitness to peak cognitive performance is mounting and providing good reason to get up and get active.

Every dietitian knows there are plenty of good reasons to encourage clients to exercise regularly. In addition to keeping obesity at bay and stress levels manageable, physical activity reduces the risk of cardiovascular disease, colon and breast cancer, type 2 diabetes, osteoporosis, and even depression. Now researchers say another benefit belongs on this list: improved brain function.

An increasing amount of evidence points to the theory that physical activity—specifically aerobic activity—keeps the mind sharp and the brain healthy, not only by preventing natural age-related declines but also by enhancing and improving cognitive functions (eg, learning, memory, multitasking).1-3 Although the research is still in its early stages, it has consistently reported these positive associations across the life span—from the very young to the very old—and in both men and women.1,3

These important findings give dietitians and their clients more reason to get up, get out, and get moving, regardless of age.

A Little Goes a Long Way
Although scientists recognized the link between physical activity and cognition in the 1930s, it wasn’t until the past decade or two, when several large observational studies found physically fit individuals performed better on cognitive function tests and had faster psychomotor speed than their sedentary counterparts, that scientists began seriously investigating this relationship.1 Given our aging population, longer life spans, and rising rates of Alzheimer’s disease and dementia, it’s not surprising that most of these studies focus on older adults.2 What is surprising is that it doesn’t take much exercise to make a difference.

A 2004 Harvard University study by Weuve and colleagues examined cognitive function and self-reported exercise habits (particularly walking) of 18,766 nurses aged 70 to 81 over a two-year period. The researchers found a direct relationship between physical activity and cognition showing that the more active the women were, the higher they scored on a variety of cognitive measures and the less cognitive decline they exhibited (about 20% lower than their sedentary counterparts). Furthermore, vigorous activity wasn’t the only exercise to yield a benefit. Walking three times per week (for a total of 11⁄2 hours) at 30 minutes per mile also improved cognitive performance.

Yaffe et al reported similar results in a July 2001 study from the University of California that specifically looked at walking and cognitive function in women older than the age of 65. That time, researchers assessed physical activity and cognitive function in nearly 6,000 women and followed up with them six to eight years later. The most active women had a 30% lower risk of cognitive decline. Interestingly, it was walking distance, not walking speed, that made a difference.

But the type of activity does matter. Only when the body gets the blood pumping (as in aerobic activity such as bicycling, running, and walking) are there changes in cognitive function.

“There’s something about aerobic activity that stimulates the brain that is not observed with nonaerobic activity like stretching, toning, and weight lifting,” says Henriette van Praag, PhD, an investigator at the Laboratory of Neurosciences at the National Institute on Aging in Baltimore. “It could be that effects of strength training are more restricted to the muscle and so may not activate the brain the same way. But we really don’t know.”

Research may soon reveal the benefits of some forms of nonaerobic activity, though. A study published in the Archives of Internal Medicine in January found that once- or twice-weekly resistance training in older women improved attention and conflict resolution compared with those subjects only in balance and tone training.

It’s Never Too Late
What does exercise do for people whose memory is already fading? Several studies show that regular exercise can reduce the risk of any further declines and may even improve cognitive function.

The latest population-based study from the Mayo Clinic in Minnesota, published in the Archives of Neurology in January, determined that moderate exercise such as walking, hiking, swimming, and taking aerobics classes in midlife (ages 50 to 65) and later life (median age of 80) reduced subjects’ odds of developing mild cognitive impairment (MCI) by 39% and 32%, respectively. Since people with MCI are more likely to develop Alzheimer’s disease later in life, scientists believe exercise may help control the disease. However, research is only preliminary.4

Start Early to Improve Function
“Typically, cognitive function declines as people get older, but some people decline faster than others,” says Charles Hillman, PhD, an associate professor of kinesiology at the University of Illinois at Urbana-Champaign. “Sedentary elderly people deteriorate more steeply than physically fit people, so exercise may have a pronounced effect. But the positive effects of exercise can also be seen in young adults and children.”

Much of Hillman’s work centers around physical fitness and cognition earlier in the life span, particularly in preadolescents (9- to 10-year-olds) and young adults. Evidence is accumulating that regular aerobic exercise can actually enhance academic achievement. Among other findings, Hillman’s studies show that compared with their less fit counterparts, children who are more fit score higher on standardized achievement tests (particularly for math and reading) and have better attention skills, processing speed, self-monitoring abilities, and working memory.1-5

“What’s interesting is that physical activity effects differ between young and old,” says Art Kramer, PhD, a professor of neuroscience and psychology at the University of Illinois and Hillman’s colleague. “In the older brain, physical activity benefits [are] largest for executive control processes, which include working memory, multitasking, planning, scheduling, and dealing with ambiguity. In kids, the effect is more general and includes a broader range of tasks.” This means that physical activity may be involved in more areas of the younger brain, too.1-6

How exercise works its magic on the brain is still unknown, but scientists believe they are beginning to unravel the mystery. One possibility is that physical activity in childhood could increase the brain’s resilience by stimulating cell growth and resulting in cognitive reserve. Similar to the way increasing bone density early in life guards against later osteoporosis, building a large cognitive reserve can help protect against cognitive decline and dementia later in life.3-7 A few longitudinal population-based studies comparing self-reported cardiovascular fitness during teenage years and early adulthood to cognitive function later in life support this theory.

 One 2009 study based in Sweden correlated better cardiovascular health among teenage boys with higher intelligence scores on tests and more education and income later in life. As researchers expected, these scores were not affected by muscle strength. Another study associated better fitness levels early in life with faster information-processing speed in adulthood.3,7,8

Cognitive reserve, however, isn’t the only theory scientists are exploring. Recent research suggests that fitness in preadolescent children may actually influence brain development and neural organization, potentially changing the brain’s structure and function.6 In fact, scientists suspect exercise-induced physical changes in the brain can happen in the old and the young.

A Brain Change
The idea that fitness can change the brain’s physiology didn’t catch on until recently, when technological advancements (eg, neuroimaging techniques such as MRI and event-related brain potential, which measures brain response) allowed scientists to examine the brain on a molecular and cellular level.1,2 Driven by a large body of animal studies and several human clinical trials, these studies did much to expand our understanding of exactly how physical activity affects brain function.   

For instance, in a 2008 Taiwanese study, mice that exercised on a treadmill for five weeks grew 2.5 times more new brain cells than their nonactive counterparts. Furthermore, these new neurons quickly assimilated into the existing brain network, increasing the quality and quantity of the neurons.9

Other animal studies show that these new brain cells are accompanied by a growth in new capillaries and a richer, more extensive vascular network. A better vasculature not only provides more oxygen-rich blood to the brain but also enhances neurotransmission by improving synaptic plasticity (the ability of two neurons to “talk” to each other).1,3-10
“In addition to stimulating the production of neurons and changing the vasculature of the brain, aerobic activity upregulates a number of growth factors like insulin-growth factor 1 and brain-derived neurotrophic factor that may grow and repair the brain,” says van Praag. “This may not happen with strength training, probably because [aerobic activity causes] increased blood flow and better transportation [of these growth factors] throughout the brain.”

Hillman concurs: “Physical fitness actually shifts where the blood flows in the brain, specifically preserving brain cells in the prefrontal cortex and the hippocampus.” These areas are associated with higher order cognition.1,10

Thanks to MRI neuroimaging techniques, scientists were able to pinpoint some of these changes in humans, specifically in older adults. A 2006 study in the Journal of Gerontology split 59 healthy 60- to 79-year-olds into two groups: an aerobic training group and a toning and strengthening group. After six months, researchers examined brain volume. Subjects in the aerobic group had significant increases in both gray and white matter compared with the nonaerobic group. These are the same regions that show substantial age-related decline.10,11

Room for Improvement
While the implications of physical activity and brain function research can have tremendous potential public policy and clinical impact on preserving brain health and reducing risk of dementia, unknowns remain. “We don’t know how much exercise we need, the duration, and at what intensity is needed to get these effects,” says van Praag.

“We know single bouts of exercise improve cognitive performance regardless of how physically fit a person is,” says Hillman. “We also know that having a fit lifestyle has long-lasting effects, which appear to be continuous. But we don’t yet know how these effects work and why.”

Other questions concern gender issues, as some research shows women have a greater cognitive response to exercise than men, and which specific areas of the brain exercise affects.12 Research has also hinted at the idea that other outside factors (eg, diet, social interaction, hormone levels) influence exercise’s effect on cognition and vice versa.1

Diet has been an especially hot topic. Unfortunately, despite a flurry of media attention, there is little real research showing a relationship between what we eat and how we think (specifically related to improving memory), much less between how exercise enhances this relationship. 

“Only two studies, both of animal origin, have found a synergistic relationship between exercise and the omega-3 fatty acid DHA,” says van Praag. “But what we really need first is to understand exactly how dietary compounds act on the brain—their mechanism. Then we can look at how exercise enhances this effect.”

The two studies van Praag is referring to are both by Fernando Gomez-Pinilla. One gave rats DHA supplements and then divided them into exercise and nonexercise groups. When evaluated for learning and memory, the DHA-exercise rats performed better on learning and memory tests than rats given DHA alone without exercise.3,13

In addition to DHA (which is found in fish), tea, cocoa, spices, and fruits such as grapes, blueberries, and strawberries are also thought to benefit memory in rodents mainly because of their flavanol content.3,14,15 Recently, a study conducted at Utah State University and presented at the 2009 International Conference on Alzheimer’s Disease connected the Dietary Approaches to Stop Hypertension diet to a lower risk of cognitive decline and dementia. Based on the results, scientists believe four of the nine food groups—whole grains, vegetables, low-fat dairy, and legumes and nuts—may be responsible for the benefit. 

Move It, Don’t Lose It
Even though the way in which exercise affects the brain is still a mystery, we do know that staying physically fit keeps the brain healthy and strong. With that in mind, there’s really no reason not to recommend activity to your clients. “Getting some mild to moderate exercise every day is easy, inexpensive, and doesn’t take much time, plus it has no side effects,” says Kramer.

What could be better than that?

— Diane Welland, MS, RD, is a dietitian and freelance food and nutrition writer based in Springfield, Va.

 

References
1. Hillman CH, Erickson KI, Kramer AF. Be smart, exercise your heart: Exercise effects on brain and cognition. Nat Rev Neurosci. 2008;9(1):58-65.

2. Kramer AF, Erickson KI. Capitalizing on cortical plasticity: Influence of physical activity on cognition and brain function. Trends Cogn Sci. 2007;11(8):342-348.

3. van Praag H. Exercise and the brain: Something to chew on. Trends Neurosci. 2009;32(5):283-290.

4. Lautenschlager NT, Cox KL, Flicker L, et al. Effect of physical activity on cognitive function in older adults at risk for Alzheimer’s disease: A randomized trial. JAMA. 2008;300(9):1027-1037.

5. Castelli DM, Hillman CH, Buck SM, Erwin HE. Physical fitness and academic achievement in third- and fifth-grade students. J Sport Exerc Psychol. 2007;29(2):239-252.

6. Hillman CH, Buck SM, Themanson JR, Pontifex MB, Castini DM. Aerobic fitness and cognitive development: Event-related potential and task performance indices of executive control in preadolescent children. Develop Psychol. 2009;45(1):114-129.

7. Dik M, Deeg DJ, Visser M, Jonker C. Early life physical activity and cognition at old age. J Clini Exp Neuropsychol. 2003;25(5):643-653.

8. Aberg MA, Pedersen NL, Torén K, et al. Cardiovascular fitness is associated with cognition in young adulthood. Proc Natl Acad Sci USA. 2009;[Epub ahead of print].

9. Chih-Wei W, Ya-Ting C, Lung Y, et al. Exercise enhances the proliferation of neural stem cells and neurite growth and survival of neuronal progenitor cells in dentate gyrus of middle-aged mice. J Appl Physiol. 2008;105:1585-1594.

10. Colcombe SJ, Erickson KI, Scalf PE, et al. Aerobic exercise training increases brain volume in aging humans. J Gerontol A Biol Sci Med Sci. 2006;61(11):1166-1170.

11. Erickson KI, Kramer AF. Aerobic exercise effects on cognitive and neural plasticity in older adults. Br J Sports Med. 2009;43(1):22-24.

12. Baker LD, Frank LL, Foster-Schubert K, et al. Effects of aerobic exercise on mild cognitive impairment. Arch Neurol. 2010;67(1):71-79. 

13. Wu A, Ying Z, Gomez-Pinilla F. Docosahexaenoic acid dietary supplementation enhances the effects of exercise on synaptic plasticity and cognition. Neuroscience. 2008;155(3):751-759.

14. Gómez-Pinilla F. Brain foods: The effects of nutrients on brain function. Nat Rev Neurosci. 2008;9(7):568-578.

15. van Praag H, Lucero MJ, Yeo GW, et al. Plant-derived flavanol (-)epicatechin enhances angiogenesis and retention of spatial memory in mice. J Neurosci. 2007;27(22):5869-5878.

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