The American Cancer Society estimates that this year, 241,000 women will learn they have breast cancer and 40,000 women will die of it. Fortunately, a growing list of effective therapies developed during the past decade has helped extend lives, one reason that deaths from breast cancer have been dropping slowly since 1990. Living among us are more than 2 million women who have undergone breast-cancer treatments.
Modern miracle drugs like tamoxifen and raloxifene routinely cut risk for breast cancer in women whose medical histories or genes make them especially vulnerable to it. But reams of research also suggest that exercise—an activity as old as the human race—substantially reduces the odds of ever getting the disease, lengthens survival and considerably enhances quality of life for women with breast cancer.
Scientists don’t completely understand why exercise is so important, but they’re actively looking for answers. Roughly two thirds of all breast cancers are considered estrogen-positive; that means that the hormone estrogen fuels their growth. The rest are estrogen-negative. Many experts believe regular exercise lowers the amount of estrogen circulating through the body in the bloodstream. So for certain types of breast cancer, less estrogen equals less fuel. Exercise also pares off hormonally active fat tissue. Fat manufactures a substance called aromatase that converts hormones known as androgens to estrogen. After menopause, when the ovaries stop cranking out high levels of estrogen, this hormonal cascade becomes the major source of estrogen in a woman’s body.
Recently two large, carefully designed studies suggested exercise may work through more than just hormonal mechanisms linked to estrogen. In a study published last month in the Archives of Internal Medicine, researchers speculated that exercise might affect tumor aggressiveness. The researchers found that long-term moderate or strenuous activity over a lifetime cut risk for developing estrogen-negative invasive breast cancers (though not estrogen-positive cancers). Since fewer therapies are effective against estrogen-negative cancers, that’s heartening news. Some earlier research on exercise suggests it lowers risk for estrogen-positive cancers, too. Scientists are also looking beyond estrogen at the effects exercise has on insulin, leptin and certain growth factors.
Regular exercise early in life, particularly around puberty, and exercise vigorous enough to suppress other reproductive hormones may make a difference, too. A 2005 multicenter study on lifetime activity matched more than 4,000 white and black breast-cancer survivors with controls. Researchers found a 20 percent decrease in breast-cancer risk for the most versus least active women.
After a woman is diagnosed, exercise can dramatically lengthen survival and lower the odds of another tumor. For up to 14 years, the Nurses’ Health Study tracked nearly 3,000 participants diagnosed with breast cancer. Researchers found that recurrence rates and deaths from breast cancer (and from all causes) dipped 26 to 40 percent among those who exercised most, compared with their sedentary peers. Brisk walking or equivalent energy-burning activity for three to five hours a week—about 30 minutes a day—netted the biggest benefits. But even being active for one to three hours a week reduced risk to some degree.
Excess pounds lower the likelihood of survival after breast cancer. But for many women, maintaining a healthy weight is often a struggle, especially during treatment. Chemotherapy or radiation can make women feel too tired to exercise. Steroids given to help ease certain side effects of chemotherapy prompt a ravenous appetite. Nausea can lead to almost continuous nibbling of comfort foods to settle queasy stomachs. Some anticancer medications that work by tampering with hormones may have a hand in weight gain, too. One such hormonal drug is tamoxifen, which keeps estrogen from entering breast cells by blocking receptors inside the cells that allow access. Studies have yet to confirm a connection, but many women on tamoxifen complain of watching the scale inch upward. No matter what the root cause is for weight gain, exercise of all sorts helps burn calories. And paradoxically, for those who feel too wiped out to fit exercise in, some evidence shows light to moderate activities may actually alleviate treatment-induced fatigue.
Doctors once believed upper-body resistance training was apt to trigger the chronic swelling and discomfort of lymphedema in women treated for breast cancer. Lymph is a thin, milky fluid that collects in spaces between cells. Carrying germ-battling immune cells, it seeps through a lacy network of channels in the body before draining into the circulatory system. Lymphedema occurs when lymph backs up, often in an arm or sometimes in the torso, after surgery or radiation alters lymph channels. Several recent studies suggest that a gradual approach and proper precautions make resistance training unlikely to raise the risk of developing Lymphedema or worsening it if it already exists.
That’s important news. Resistance training helps reverse the muscle loss and fat gain called sarcopenia that often follows chemotherapy and hormonal therapy. It’s helpful in other ways, too. Osteoporosis, which sets the stage for life-altering bone fractures, may be hastened by certain anticancer treatments. Chemotherapy, for example, sometimes pushes women into early menopause by prematurely shutting down their ovaries. Since estrogen helps protects bones, losing it speeds bone-thinning, particularly in the spine and hips, which are especially vulnerable to fractures. Also known to contribute to osteoporosis is a class of breast-cancer drugs called aromatase inhibitors that cut off the most plentiful supply of estrogen after menopause by interrupting the process that converts androgens into estrogen. Resistance training slows bone loss and may even strengthen bones.
Quality of life counts, too. In clinical trials, moderate to vigorous exercise programs notched up progressively to 45-minute sessions at least three times a week eased anxiety and depression, enhanced mood and self-esteem, and helped counter fatigue.
Thus far, there are few studies of exercise in women with advanced breast cancer, although early evidence suggests that physical activity offers benefits here, too, such as less fatigue. More rigorous studies investigating links between breast cancer and exercise are underway. Don’t settle back to await developments, though. Rise from your reading and head out for a walk.
title: “Talk Transcript Mary Carmichael On Exercise And The Brain” ShowToc: true date: “2022-12-30” author: “Robert Birks”
For several decades we’ve known about one effect of exercise on the brain, the “endorphin high” that makes us feel good during and right after exercise. Recently, scientists have uncovered some longer-lasting effects of exercise on the brain. Regular exercise improves your mood, decreases anxiety, improves sleep, improves resilience in the face of stress and raises self-esteem. All these benefits don’t come because you notice what you’ve lost around your waist. Rather, they come from exercise-induced alterations inside your head.
With exercise, several biological changes occur that make your nerve cells more robust. The blood and energy supply to the brain improves. The genes in nerve cells signal the production of proteins called neurotrophic factors or growth factors. These substances induce nerve cells to grow, branch and make connections with one another (neuroplasticity) and—in some brain areas—give rise to new nerve cells (neurogenesis). These important biological processes, which are essential to adaptation and learning, tend to slow down with age and also in response to stress, after brain injury and in depression. Exercise can speed the process back up again, making it a respectable, though partial, antidote to stress and aging.
Exercise is a pretty good antidepressant, too—equal to drugs or psychotherapy in some studies. Exercise and antidepressant medications also appear to be biologically equivalent. Consider the hippocampus, a seahorse-shaped region in the temporal lobe of the brain. It is involved in regulating mood and storing memories. When neuroplasticity and neurogenesis are sluggish, the hippocampus gets smaller. Neuroscientists see this in brain scans of people with depression. Antidepressants and electroconvulsive therapy appear to spur nerve growth in this region. Exercise probably relieves—and likely also prevents—depression through the same mechanism.
Using an animal model of depression well known among neuroscientists, researchers at the Karolinska Institute in Sweden demonstrated these changes in the brain in a series of experiments. They saw that “depressed” rats grow more nerve cells in the hippocampus in response to exercise. Then, by measuring the levels of mRNA, an indicator of gene activity, they found that exercise caused an increase in the production of neuropeptide Y (NPY) in the hippocampus. Also working with rats, a group at California State University found that exercise induced an increase in brain-derived neurotrophic factor (BDNF) in the same region. These two proteins—NPY and BDNF—are important prerequisites for nerve growth and survival.
Just knowing what exercise can do for your brain won’t guarantee that you’ll jump off your couch and start jogging down the road. You still need motivation, but where does it come from? Even that is under genetic control.
Recent research finds that the brain governs how much activity your body is ready for, in part using signals from your muscles as a guide. The theory goes that the brain needs to be in charge, to regulate energy output and preserve the integrity of the whole body. In this model, the brain decides when you need to be active and when you don’t. How good a job your brain does at managing this is genetically determined. And, just as with weight control, the brain isn’t always right: just as the brains of overweight people often make them hungry, the brains of some inactive people often encourage even more inactivity.
Indeed, some researchers are beginning to wonder if genes that make a person vulnerable to depression also make exercise less pleasant—or less reinforcing. Exercise has been demonstrated so effective at reducing health risks with so few adverse effects that it should be an easy sell. Yet no one has yet found the most effective way to promote a healthy lifestyle. Information about the positive effects of exercise does not seem to be enough. To improve motivation for exercise, it would help us to better understand how our genes control our experience of exercise.
At the University of Colorado at Boulder, investigators have developed a model of exercise behavior to guide their research. They make the reasonable assumption that genes influence both our physiological responses to exercise (for example, our heart rate or body temperature) and our subjective experience of it (how our moods change or how tired we feel). They conducted a study in which participants were assigned to periods of both exercise and inactivity. The subjects’ responses were recorded. The researchers, knowing that there are two forms of a gene involved in BDNF function, also determined the genotype of each subject. The results suggested that the degree of mood improvement and the perception of exertion was partly determined by the form of the participant’s BDNF gene.
These are very early returns, so in the meantime some practical advice may help. You don’t have to invest in fancy equipment or a health club to get the benefits of exercise. Vigorous, sweat-inducing effort is a good thing, but psychological well-being or an improvement in depressive symptoms does not seem to depend upon the intensity or duration of the workout. More important is your ability to sustain an exercise routine. The research indicates that if you can stick with any program for at least two months, you’re giving yourself the best chance to feel better. Fortunately, there does appear to be a priming effect—after a while it gets easier to continue, and some people end up describing their exercise as a habit they enjoy continuing.
The type of exercise also doesn’t seem to matter much—aerobic exercise and strength training or a combination are equally effective. Thirty minutes per day of moderate exercise—a brisk walk, for example—can help. Start even smaller if you want to. Build 10 minutes of walking into your daily commute by parking a little farther from the office. Take stairs instead of an elevator. There is some evidence that exercise is more pleasant if you stay hydrated. So if you are going to exercise for any extended period, drink water before you start and again every so often during the workout. And if your exercise program is boring, keep yourself stimulated during exercise: listen to music or an audiobook.
You may have concluded that you are one of those people with I-don’t-feel-much-like-exercising genes. But if you find the science convincing, begin to picture healthy nerve cells plumping and sprouting. Does that motivate you? If not, let’s hope that scientists will soon find that gentle nudge—new information, a form of psychotherapy or a medication—that will help you feel like it and keep you moving. Whoever finds the starter motor, the genetic wellspring of motivation, will have found a key to good health.
title: “Talk Transcript Mary Carmichael On Exercise And The Brain” ShowToc: true date: “2022-12-10” author: “Alma Cam”
At this point, most adults would vow to change their habits, only to sink back into the comfort of the living-room couch. Not Chugg. After attending a Senior Olympics event with his son, Ben, a high-school track athlete, he made a drastic change: he quit his six-figure job and decided to devote himself full time to training for this summer’s National Senior Games in Louisville, Ky. (For now, he’s trying to make ends meet as an amateur art dealer.) After passing a stress test at his doctor’s office, he began walking every day, then jogging. Then he hired Ben, 15, as his coach and started running hard. Last September Chugg qualified for Louisville with a bronze medal in the 100-meter dash and a silver in the long jump at a regional meet. More important, his blood pressure is down and he hasn’t had a problematic blood-sugar reading in months. “It’s changed my life,” he says.
Chugg is an example of how high-intensity exercise can rapidly improve your health. Research has shown for decades that people who work out regularly are at lower risk for such health problems as obesity and heart disease. While the benefits of moderate exercise are much greater than little or no exercise, several recent studies have shown that vigorous exercise is even better for you. (Vigorous is defined as working at 60 percent or more of aerobic capacity; moderate is 40 to 60 percent.) Specifically, it’s more effective at lowering blood pressure, improving insulin sensitivity (which can reduce the risk of developing diabetes) and raising one’s aerobic capacity. “Almost all cardiovascular risk factors respond significantly better to vigorous exercise than to moderate exercise,” says Brian Duscha, a clinical researcher who specializes in exercise physiology at the Duke University School of Medicine.
Participating in a competitive sport can help you stick with a high-intensity routine. Many people find it difficult, if not impossible, to make the kinds of lifestyle changes necessary to go from couch potato to gym regular. Joining a team forces you to do things that you might not otherwise do. Not only is it fun, but you have an obligation to show up for practices and events. There are teammates to work out with, and there’s usually a coach on hand to keep track of your progress, help set new goals.
William Gillies, 38, used to look forward to frequent after-work pub crawls with friends. But after he joined a marathon training program organized by the New York City running shop Urban Athletics, his priorities shifted. “My coach would give me a hard time whenever I missed a session,” he says. He taught Gillies about proper nutrition and “instilled the spirit of competition” in him. Susan von der Lippe, 41, a former Olympic swimmer from Loveland, Colo., does laps with a USA Swimming masters club three mornings a week and competes in meets once a month. “The camaraderie and the competition is what keeps me involved,” she says. “I like setting myself goals and seeing how fast I can make this old body move.”
In a recent study, Duscha and his co-workers showed exactly how high-intensity exercise can improve health. The Duke group divided 282 overweight and sedentary adults (read: your average American) between the ages of 40 and 65 into four groups and had each group exercise at a different intensity three or four times a week over the course of nine months. One group did a lot of high-intensity exercise—the equivalent of running 20 miles per week fairly quickly. Two other groups did low amounts of high-intensity or moderate-intensity exercise—the equivalent of running 12 miles per week fairly quick-ly or at a moderate pace, respectively. A fourth group, the control, did no ex-ercise. Overall, says Duscha, when compared with fitness improvements in other clinical studies, the group that exercised a lot at a high intensity lowered its risk of dying from a heart attack by 24.5 percent, as compared with 14.5 percent and 8.1 percent for the other exercise groups. Those in the two high-intensity groups also reduced their concentrations of a specific LDL-cholesterol particle that can clog arteries and lowered their body-fat percentages. They also raised their aerobic capacity more than the moderate-intensity group.
Interestingly, moderate exercise appears to lose out to vigorous exercise no matter how many calories it burns. In a review published last year in The American Journal of Cardiology, David Swain, a professor of exercise science at Old Dominion University in Norfolk, Va., and Barry Franklin, director of cardiac rehabilitation at William Beaumont Hospital in Royal Oak, Mich., analyzed a dozen studies like Duscha’s that compared exercise intensity with coronary-heart-disease risk. In each case, they controlled for the subjects’ total energy expenditure, or the number of calories burned. Those who exercised vigorously had greater improvements in aerobic capacity and glucose control (which predicts one’s risk of developing diabetes) and greater reductions in blood pressure.
While doctors know that high-intensity workouts improve health more than low- intensity ones, they don’t know exactly why. One clue may lie in the inflammatory process, a cascade of events that can lead to health problems such as clogged coronary arteries. In a pilot study concluded last summer at Columbia University Medical Center, researchers found that moderate and intense aerobic exercise lowered levels of tumor necrosis factor (TNF), which plays a key role in the inflammatory process. Study leader Dr. Richard Sloan, a professor of behavioral medicine at Columbia, is planning a broader study that will examine, among other things, whether high-intensity workouts have a greater impact on inflammation than moderate-intensity ones.
Vigorous exercise also holds benefits that can’t be measured in a lab. Since Jessica Kavoulakis, 40, a lawyer from New York City, joined a marathon training program two years ago, she’s gained a new sense of purpose, ambition and self-confidence. “I saw my body do things I never thought it could do,” she says. Steve Chugg believes his improved fitness has made him a better father, a better friend and “an all-around better person, psychologically.” For Marilyn Minnick, 60, who qualified for the 2007 Senior Olympics with her three sisters and two close friends, the experience has brought the group closer. “We do things together all the time now, so it’s really fun,” she says. “We just laughed our heads off at the state games when we qualified.” Minnick’s group will compete in cycling and track and field.
How much vigorous exercise does one need? The U.S. Centers for Disease Control and Prevention recommend that adults engage in at least 30 minutes of moderate-intensity exercise—an activity you can do while breathing harder than normal and still carry on a conversation—on five or more days of the week. Another CDC option is 20 minutes of high-intensity exercise—an activity you can do for several minutes at a time but during which you’re unable to speak in complete sentences—at least three days per week.
Doctors emphasize, however, that vigorous workouts are not for everyone. Adults with risk factors for heart disease such as diabetes or high blood pressure should take an exercise stress test before starting any activity program, says Swain. Those who are healthy but sedentary should start slow and work up to a more rigorous program over the course of three to six months. “But if you cannot ever make it to a vigorous level, that’s fine,” says Duscha. “Our study results show low levels of exercise are very beneficial in reducing cardiovascular risks.”
Even though she works out with a top coach, Kavoulakis tore a hamstring muscle last year. Now recovered, she’s set on not just crossing the finish line of the New York City Marathon in November but running the event quickly enough to qualify for the Boston Marathon in April 2008. For Kavoulakis and many others, the thrill of competitive sports lies in setting goals you never thought you could achieve—then meeting them.
title: “Talk Transcript Mary Carmichael On Exercise And The Brain” ShowToc: true date: “2022-12-14” author: “Christopher Cummings”
Cardiologists have long hoped for a drug to boost HDL as efficiently and with as few side effects as the statin drugs reduce LDL (“bad” cholesterol). Together, the two approaches could provide a potent, double-barreled weapon against heart disease. While excess LDL causes formation of arterial plaques, leading to heart attacks and strokes, HDL actually clears cholesterol out of the plaques, reducing risk. “Increasing HDL is like sending out more garbage trucks to get rid of junk in the arteries,” says Dr. Ronald Krauss, a cholesterol researcher at Children’s Hospital Oakland Research Center. “If we had the right new drug to raise it, millions of people might benefit.” Torcetrapib raised HDL by 50 percent. So how did it go wrong? And is the problem specific to this drug or common to all similar medicines in development?
For the moment, pharmaceutical companies are still pursuing other drugs in the same class as torcetrapib. These pills all target a protein known as CETP, which is involved in the recycling of cholesterol. Researchers began focusing on it as early as 1990, when a study in The New England Journal of Medicine noted that Japanese subjects with naturally low levels of CETP had stunningly high HDL—often exceeding 100 milligrams per deciliter. (Normal levels are 40 or above in a man and 50 or more in a woman.)
Whether the other CETP inhibitors have a future will become clearer this weekend at the annual meeting of the American College of Cardiology. It’s common knowledge among researchers that torcetrapib raised blood pressure in early tests. Scientists will reveal just how big the increase was—and, by implication, whether that was the drug’s fatal flaw. (Roche and Merck are both working on CETP inhibitors that do not appear to raise blood pressure.)
But what if the problem with torcetrapib was more fundamental, such as an adverse effect on HDL’s basic function? Presentations at ACC could shed light on that, too. In three separate trials, Nissen and other investigators scanned thousands of patients’ blood vessels before they began taking torcetrapib, and again months later. If HDL functioned well, the trials should show that arterial plaques shrank. No matter what the results, it will take years to bring a drug like this to market.
In the meantime, what’s a person who wants to boost HDL to do? The drug Niaspan—a version of the B-vitamin niacin—raises it as much as 25 percent, although it can cause flushing that resembles menopausal hot flashes. (The “no-flush niacin” in health-food stores doesn’t raise HDL, so save your money.) You can also nudge up HDL through lifestyle changes. Exercise lifts levels by about 5 percent—or more, if you work out an hour a day. Weight loss helps, too, especially shedding abdominal fat. So does a healthy diet that’s low in trans fats and processed sugar, but high in fish, whole grains, fruits, vegetables and legumes. Quitting smoking gives you another boost. And for your reward after all that hard work, moderate alcohol intake—defined as one glass a day for women and two for men—also elevates HDL a little. True, the collective impact does not rival the 50 percent boost from torcetrapib. On the other hand, these measures help in other ways that simply raising HDL alone does not. “If heart disease is the product of the wrong diet, obesity and smoking cigarettes, it’s hard for me to believe the answer is for everyone to take medications,” says Dr. Sidney Smith of the University of North Carolina, Chapel Hill, past president of the American Heart Association. It’s a message we should all take to heart.
title: “Talk Transcript Mary Carmichael On Exercise And The Brain” ShowToc: true date: “2022-12-08” author: “Louie Givens”
For several decades we’ve known about one effect of exercise on the brain, the “endorphin high” that makes us feel good during and right after exercise. Recently, scientists have uncovered some longer-lasting effects of exercise on the brain. Regular exercise improves your mood, decreases anxiety, improves sleep, improves resilience in the face of stress and raises self-esteem. All these benefits don’t come because you notice what you’ve lost around your waist. Rather, they come from exercise-induced alterations inside your head.
With exercise, several biological changes occur that make your nerve cells more robust. The blood and energy supply to the brain improves. The genes in nerve cells signal the production of proteins called neurotrophic factors or growth factors. These substances induce nerve cells to grow, branch and make connections with one another (neuroplasticity) and—in some brain areas—give rise to new nerve cells (neurogenesis). These important biological processes, which are essential to adaptation and learning, tend to slow down with age and also in response to stress, after brain injury and in depression. Exercise can speed the process back up again, making it a respectable, though partial, antidote to stress and aging.
Exercise is a pretty good antidepressant, too—equal to drugs or psychotherapy in some studies. Exercise and antidepressant medications also appear to be biologically equivalent. Consider the hippocampus, a seahorse-shaped region in the temporal lobe of the brain. It is involved in regulating mood and storing memories. When neuroplasticity and neurogenesis are sluggish, the hippocampus gets smaller. Neuroscientists see this in brain scans of people with depression. Antidepressants and electroconvulsive therapy appear to spur nerve growth in this region. Exercise probably relieves—and likely also prevents—depression through the same mechanism.
Using an animal model of depression well known among neuroscientists, researchers at the Karolinska Institute in Sweden demonstrated these changes in the brain in a series of experiments. They saw that “depressed” rats grow more nerve cells in the hippocampus in response to exercise. Then, by measuring the levels of mRNA, an indicator of gene activity, they found that exercise caused an increase in the production of neuropeptide Y (NPY) in the hippocampus. Also working with rats, a group at California State University found that exercise induced an increase in brain-derived neurotrophic factor (BDNF) in the same region. These two proteins—NPY and BDNF—are important prerequisites for nerve growth and survival.
Just knowing what exercise can do for your brain won’t guarantee that you’ll jump off your couch and start jogging down the road. You still need motivation, but where does it come from? Even that is under genetic control.
Recent research finds that the brain governs how much activity your body is ready for, in part using signals from your muscles as a guide. The theory goes that the brain needs to be in charge, to regulate energy output and preserve the integrity of the whole body. In this model, the brain decides when you need to be active and when you don’t. How good a job your brain does at managing this is genetically determined. And, just as with weight control, the brain isn’t always right: just as the brains of overweight people often make them hungry, the brains of some inactive people often encourage even more inactivity.
Indeed, some researchers are beginning to wonder if genes that make a person vulnerable to depression also make exercise less pleasant—or less reinforcing. Exercise has been demonstrated so effective at reducing health risks with so few adverse effects that it should be an easy sell. Yet no one has yet found the most effective way to promote a healthy lifestyle. Information about the positive effects of exercise does not seem to be enough. To improve motivation for exercise, it would help us to better understand how our genes control our experience of exercise.
At the University of Colorado at Boulder, investigators have developed a model of exercise behavior to guide their research. They make the reasonable assumption that genes influence both our physiological responses to exercise (for example, our heart rate or body temperature) and our subjective experience of it (how our moods change or how tired we feel). They conducted a study in which participants were assigned to periods of both exercise and inactivity. The subjects’ responses were recorded. The researchers, knowing that there are two forms of a gene involved in BDNF function, also determined the genotype of each subject. The results suggested that the degree of mood improvement and the perception of exertion was partly determined by the form of the participant’s BDNF gene.
These are very early returns, so in the meantime some practical advice may help. You don’t have to invest in fancy equipment or a health club to get the benefits of exercise. Vigorous, sweat-inducing effort is a good thing, but psychological well-being or an improvement in depressive symptoms does not seem to depend upon the intensity or duration of the workout. More important is your ability to sustain an exercise routine. The research indicates that if you can stick with any program for at least two months, you’re giving yourself the best chance to feel better. Fortunately, there does appear to be a priming effect—after a while it gets easier to continue, and some people end up describing their exercise as a habit they enjoy continuing.
The type of exercise also doesn’t seem to matter much—aerobic exercise and strength training or a combination are equally effective. Thirty minutes per day of moderate exercise—a brisk walk, for example—can help. Start even smaller if you want to. Build 10 minutes of walking into your daily commute by parking a little farther from the office. Take stairs instead of an elevator. There is some evidence that exercise is more pleasant if you stay hydrated. So if you are going to exercise for any extended period, drink water before you start and again every so often during the workout. And if your exercise program is boring, keep yourself stimulated during exercise: listen to music or an audiobook.
You may have concluded that you are one of those people with I-don’t-feel-much-like-exercising genes. But if you find the science convincing, begin to picture healthy nerve cells plumping and sprouting. Does that motivate you? If not, let’s hope that scientists will soon find that gentle nudge—new information, a form of psychotherapy or a medication—that will help you feel like it and keep you moving. Whoever finds the starter motor, the genetic wellspring of motivation, will have found a key to good health.
