Successful Aging: A Neuroscientist Explores the Power and Potential of Our Lives

by Daniel J. Levitin

Children who are delivered via Caesarean section show a reduced diversity of their gut microbiome.

The full extent of gut-brain interactions is still unknown, but links between these interactions and an imbalanced microbiome have been implicated in mental disorders as diverse as autism, schizophrenia, ADHD, bipolar disorder, and multiple sclerosis. A credible although still unconfirmed view is that an imbalanced microbiome during infancy and childhood can lead to these conditions and diseases later in life. But that doesn’t mean the conditions are irreversible. Probiotics as contained in foods and supplements can introduce or reintroduce beneficial bacteria into the gut.

But where it really gets interesting is the effects that probiotics can potentially have on cognition, emotion, and behavior. Small-scale trials have shown that a single probiotic, Bifidobacterium infantis, can alleviate depression and anxiety, and a cocktail of Lactobacillus helveticus and Bifidobacterium longum can reduce cortisol levels—an indicator of stress. A preliminary report finds that a probiotic mixture containing Bifidobacterium lactis, Lactobacillus bulgaricus, Streptococcus thermophilus, and Lactobacillus lactis can substantially alter brain activity in the mid- and posterior insula, regions associated with anxiety disorders and attentional focus. Kefir, yogurt, and other fermented milk products containing probiotics have been shown to have a positive effect on mood and the brain’s emotional centers. And emerging evidence suggests that eating more fiber promotes gut health and microbiomic balance.

it’s usually suggested that probiotics be taken with a meal that contains prebiotics. Prebiotics are specialized plant fibers found in many fruits and vegetables, especially those that contain complex carbohydrates. These carbohydrates aren’t digestible, so they pass through the digestive system to become food for the bacteria and other microbes. Dozens of foods act as prebiotics, including apples, asparagus, bananas, chicory root, garlic, honey, mushrooms, seaweed, wheat bran, yams, and yogurt.

Pontzer notes that one reason hunter-gatherers tend not to have obesity is the lack of variety in any given individual hunter-gatherer’s diet. When we have a lot of food choices, we tend to overeat because the variety of flavors is enticing. “It’s the reason you always have room for dessert at a restaurant even when you’re full,” Pontzer says. Even though you’re full “and you can’t eat one more bite of steak, you’re still interested in the cheesecake because it’s sweet and that button hasn’t been worn out in your brain yet.”

Why don’t diets work? First off, the fact that a multi-billion-dollar diet industry still exists suggests that there’s something fundamentally broken about the way we look at food and eating.

Diets don’t work because they are based on restriction. God forbid you touch carbs, our most fundamental source of energy, lest they go straight to your waistline. Restriction subsequently fosters deprivation, and ultimately, you’re left craving all of the foods you’ve been told are off-limits. . . .

The big idea of intuitive dieting is that your body knows what kinds of food you need—that it has an intuitive drive toward protein, carbs, and fats you can trust. Or perhaps it’s the trillions of microbes in your gut that send signals to your brain to generate that intuitive drive. Maybe your body knows what it wants to eat. The four additional principles of intuitive dieting are: try to eat when you’re hungry; try to stop when you’re no longer hungry; learn to cope with emotions in alternative forms, other than eating; and place no restrictions on types of food eaten unless for medical reasons.

intuitive eating involves a reframing of eating for physical rather than emotional or social reasons. Thus, knowing that any food option is on the table, so to speak, makes you less likely to binge eat the forbidden foods. Proponents of intuitive eating, such as Mallory Frayn, talk about cultivating a less obsessive, healthier relationship with food and allowing the body to experience a healthy variety—in moderate amounts—of all the foods that are available to us. And all of this should be informed by good sense, and the knowledge that although you might consume them once in a while, the chocolate-cake-and-onion-rings diet is not a good long-term strategy for optimal health.

The key to diet seems to be not what you eat, but what you don’t. The American diet is too high in processed foods, sugar, salt, and red meat. Junk food is addictive—it overstimulates the brain’s reward system, which evolved in an era when fats and sweets were hard to come by. Apart from that, the fact is, we just don’t know enough about nutrition to say that there is a single best diet. As a report on the state of nutritional advice at Stanford University noted, “The history of nutrition science is littered with the remains of hypotheses that were once the next big thing.”

what does seem to be clear is that large amounts of refined sugar, deep-fried foods, and heavily processed foods are unhealthy. Apart from that, eating a variety of different foods, in moderation, and eating more vegetables than the average American currently consumes, all appear to contribute to longevity and health. Reducing the use of tobacco and alcohol is also indicated. After reviewing hundreds of papers, I find that the best dietary advice for older adults is the much-quoted phrase in Michael Pollan’s 2008 book In Defense of Food: “Eat food. Not too much. Mostly plants.” And allow yourself to have fun now and then. Eat a little ice cream. Have some chocolate.

EXERCISE Movement matters

we humans were not made to be sedentary. We evolved in a world that required us to explore the environment, to move. Without that stimulation the brain ceases to function at its full potential . . . and can easily go into a tailspin. In his new book, Physical Intelligence: The Science of How the Body and the Mind Guide Each Other Through Life, Scott Grafton, a neuroscientist and practicing neurologist at UC Santa Barbara, proposes that the enormous complexity of the human brain is primarily there to organize movement and action. When we cease to move, to explore our environment, when we no longer use our brains to organize physical action, could it be that it slows down, atrophies, and becomes disorganized?

we can ask, how to best maintain whole organismal health and well being for anyone? Step one is to eliminate the brain/body dualism. Just because some aspects of mental life and mind are intuitively separable from brain, doesn’t mean the brain (or mind for that matter) is ever really free of the body.

What is the single factor with the largest effect that benefits mental health, body structure (including brain structure), functioning across multiple domains, and longevity? It is physical activity (or its imprisoned corollary, “exercise”).

Why is all this physicality good for us? Well, there is a long list of probable reasons. My book touches on just those that make sense from a perspective of movement science: skill, adaptation and perceptual fidelity in the natural world. But there are lots of others—problem solving, social enrichment, mind-body coordination, and fresh air.

Our brains were built to move our bodies toward food and mates, and away from predators. Exercise is important for two reasons. The obvious one is that it oxygenates the blood. The brain runs on oxygenated glucose, carried by hemoglobin in the blood, and a fresh supply of oxygen is good. The nonobvious reason is that our brains, because they were built to navigate in unfamiliar surroundings, don’t do well when they’re not challenged by having to problem solve. Every step you take on a treadmill or elliptical is helping you with the first of these two imperatives—getting your blood oxygenated—but they don’t help your brain to keep its navigational skills and memory systems honed. Every minute you walk on an unpaved trail, whether in a park or in the wilderness, requires you to make hundreds of microadjustments to foot pressure, angle, and pace. These adjustments stimulate the neural circuitry of your brain in the precise way that it evolved to be used. The area that is most stimulated is your hippocampus, that seahorse-shaped structure that is critical to memory formation and retrieval. This is why so many studies show that memory is enhanced by physical activity. This way of looking at things is known as embodied cognition, the idea that physical properties of the human body, particularly the perceptual and motor systems, play an important role in cognition (thinking, problem solving, action planning, and memory). In this way of thinking, the sensation of movement is inext...

The body influences the mind just as the mind influences the body.

the most successful intellectuals are those who embrace the physical, and the most successful athletes are those who embrace the intellectual. Among my university colleagues, those who keep physically active are by far the most productive,

A systematic meta-analysis showed that for adults with mild cognitive impairment, exercise had a significant beneficial effect on memory. Adults with mild cognitive impairment have a considerably increased risk of progressing to dementia, and this specific risk is increased by atrophy of the hippocampus.

Aging is an irreversible and inescapable process. But the effects of aging are, in some cases, reversible and, if not completely escapable, at least subject to delay. There are many factors under our control—diet, gut microbiota, social networks, sleep, regular visits to the doctor. But the single most important correlate of vibrant mental and physical health is physical activity. This doesn’t mean the other correlates (diet and sleep) aren’t important—they are—and it doesn’t mean that if you engage in more physical activity you don’t need to follow other healthy practices. What it does mean is that you might want to take this seriously—particularly if, like many people, your attitude about getting active is “Yeah, yeah—I’ll start tomorrow.”

Mick Jagger (age seventy-five) works with a personal trainer. “I train five or six days a week. . . . I alternate between gym work and dancing, then I do sprints. I’m training for stamina.” Jane Fonda (age eighty-one) works out every day with long walks and weights. As Dylan Thomas advised, they are not going gently into the night. Interacting with the world also enhances creativity. The interactions don’t have to be especially complex, and they certainly don’t have to be boundary pushing or dangerous.

those who were made to walk around a rectangular path, showed significantly higher scores in a battery of creativity tests, including a divergent thinking task—we saw these in Chapter 4, on problem solving. The researchers asked participants to generate as many uses as they could for an everyday object—in this case chopsticks. Sample answers that indicate divergent thinking included using them as drumsticks, as a conductor’s baton, as a child’s magic wand, as a coffee stirrer, or to toast marshmallows. You get the idea. And the researchers found that simply walking around outside enabled a person to come up with more answers.

To me, “older adults” are those who are manifestly slowing down, physically and mentally, who can’t do many of the things they used to do, and who are discovering that the things they might want to do are becoming constricted by physical and mental limitations. A large part of the story of people who manage to stay young, in spite of their chronological age, relates to synaptic plasticity—the ability of the brain to make and form new connections. As we’ve seen, plasticity is influenced by your genetic makeup, your lifetime of experiences, and the culture in which you live. It is also influenced by your daily routines, especially as you get older. The act of transmitting information across synapses, and the forming of new synaptic connections, requires a dramatic increase in the amount of energy used in the brain.

Most effective is to engage in aerobic exercise just before learning something new. When you get your heart rate up just before a mental task, you prime the brain with increased blood flow, which creates an enriched setting for mental activity.

Sarcopenia is the loss of muscle tissue—similar to what osteoporosis is for bone. It is a leading contributor to functional decline and loss of independence in older adults. Fortunately, it can be reversed. In one study, twelve sedentary men aged sixty to seventy-two significantly increased their leg strength and muscle mass with a twelve-week strength-training program three times a week. In another study, eight weeks of resistance training created significant improvements in frail nursing home residents aged ninety to ninety-six. They saw a 174 percent gain in strength, and walking speed improved almost 50 percent. So it’s not just about endurance or blood oxygenation—maintaining muscle strength is essential as well.

For those who don’t want to do more, but really want to do less, Wisløff and others have shown that even shorter, less structured workouts are still remarkably beneficial. High-intensity interval training (HIIT) is a very short workout—thirty seconds to a minute of running, climbing stairs, or cycling—followed by a minute or two of cool-down activities, such as walking or slow pedaling. Repeat the cycle for only ten minutes and you’ve just done a HIIT. “While anything helps, a bit more is probably better,” University of Michigan researcher Weiyun Chen commented.

“We now have more than 10 years of data showing HIIT yields pretty much the exact same health and fitness benefits as long-term aerobic exercise, and in some groups or populations, it works better than traditional aerobic exercise.” The problem with most exercise programs is that the people who need them don’t find them enjoyable and therefore don’t stick with them. Time-efficient workouts, like HIIT, provide an alternative, one that the majority of participants find far more enjoyable, and that avoids the monotony of traditional programs.

How intense does a HIIT workout need to be? You should try to achieve 90 to 95 percent of your maximum heart rate during the short, high-intensity periods.

you’ll know you’ve reached the desired intensity if you can no longer carry on a conversation while running or cycling. You can still run or bike. You just can’t talk.

Even the teensiest, tiniest, barely measurable amount of physical activity improves brain function—not as much as the HIIT mentioned previously, but it is significant and it matters. The very largest improvements we’ve seen for reducing risks of cardiovascular disease and diabetes, and improving memory, come not from moderately active people who engage in a more systematic and intense program, but from sedentary people who engage in the barest minimum of physical activity—even just getting up and walking a bit.

One of the problems with exercise is that, like with dieting, people start out with overly ambitious plans that are difficult to maintain. The majority of people fail to follow through with these plans because they lose interest or find them boring or too difficult to integrate into their daily routines. For those who are out of shape, the thought of going to a gym may be intimidating. It is a fact of the gym industry that a large proportion of people who take out gym memberships end up not using them—this is one of the reasons that so many gyms require that you pay for a year in advance!

We cannot just tell people that they need to exercise more; it does not work. Our work clearly shows that we need to demonstrate lifestyle modifications that can be adopted by most of the population and get away from sending people to gyms.

Outdoors, anything can happen. And that’s the most potent way of keeping the brain flexible and active that we have so far discovered. A bustling city street can render some of these same effects, minus the hidden and ancient power of naturescapes to be mentally soothing and stimulating at the same time.

Scottish doctors have begun issuing prescriptions for “rambling and birdwatching.”

Doctors in Quebec have begun prescribing free visits to the Musée des Beaux-Arts Montreal (Montreal Museum of Fine Arts) for patients suffering from a number of physical and mental health issues, to enjoy the benefits that art can have on one’s health. Walking indoors through a museum (or even a mall) provides a high chance of coming across people and things you haven’t seen before, and the amount of ground you cover can be surprising.

When I met with His Holiness the Dalai Lama, he was eighty-three years old and had just published his 125th book. “How do you stay so mentally fit?” I asked him. “Sleep,” he said without missing a beat. “Nine hours a night.” “Every night?” “Every night.” Sleep is restorative.

The idea that older adults need less sleep is a myth. They tend to get less sleep, but they still need the eight hours that the rest of us need. Today, about half of adults sleep less than seven hours a night. Why?

First, we electrified the night. Light is a profound degrader of our sleep. Second, there is the issue of work: not only the porous borders between when you start and finish, but longer commute times, too. No one wants to give up time with their family or entertainment, so they give up sleep instead. And anxiety plays a part. We’re a lonelier, more depressed society. Alcohol and caffeine are more widely available. All these are the enemies of sleep.

We have stigmatized sleep with the label of laziness. We want to seem busy, and one way we express that is by proclaiming how little sleep we’re getting. It’s a badge of honor. When I give lectures, people will wait behind until there is no one around and then tell me quietly: “I seem to be one of those people who need eight or nine hours’ sleep.” It’s embarrassing to say it in public. . . . Humans are the only species that deliberately deprive themselves of sleep for no apparent reason.

Healthy, productive sleep allows the body to engage in cellular repair mechanisms—normal cellular housekeeping and immune-system responses—and helps us to process difficult emotions and replenish our energy levels.

One of the functions of sleep is to process the most emotionally intense experiences of the previous day, to separate the facts from our feelings so that we can reach a quasi-objective view of things. The other reason for doing so is so that the emotions themselves can be entered into and stored in memory. It is of value to be able to access a memory based not just on a particular time or a particular place (which we can all do), but also on a particular emotion. All the experiences you’ve had of being humiliated, for example, can be bound together through emotional memory, in order to help you extract patterns and (hopefully) modify your future behavior. Sleep-deprived people show a 60 percent greater activation in their amygdala during waking hours than those who are not sleep-deprived. Because the amygdala is part of the brain’s fear circuit and is known to trigger aggression, anger, and rage, this finding highlights the relation between sleep deprivation and emotional regulation. When your mom told you that you were being crabby because you didn’t get enough sleep, she was probably right.

Too little sleep, or—perhaps counterintuitively—too much sleep, impairs problem solving, attention to detail, memory, motivation, and reasoning.

If I haven’t frightened you into taking sleep seriously yet, sleep deprivation is now strongly associated with Alzheimer’s. Alzheimer’s disease occurs when a certain kind of protein, amyloid, builds up in the brain, where it forms clumps that collect between neurons, which in turn disrupt cell function. During proper, restorative sleep, these amyloid deposits get cleaned out of the brain through the action of the cerebrospinal fluid. When you’re sleep-deprived—either from short duration or poor-quality sleep—these amyloid deposits don’t get cleaned out, and they tend to selectively attack regions in the brain responsible for sleep, which then makes it even more difficult to sleep and, consequently, more difficult to clear out the amyloids. A vicious, sleepless, memory-killing cycle.

The areas most impacted by sleep deprivation were the hippocampus (memory) and the thalamus (control of sleep-wake cycles). It is becoming clear that a lack of sleep, particularly a chronic lack, can lead to Alzheimer’s disease.

Passing through non-REM and then REM sleep adds up to a sleep cycle. A great deal gets done during such cycles, and it appears that we need five or six of them to reach full restoration. How do you know whether you’re getting enough sleep? Unless you’ve got certain medical conditions or are taking medications that cause fatigue, a simple rule of thumb is that if you can’t wake up in the morning without an alarm clock and you feel sleepy before lunch, either you are sleep-deprived or, as we saw in Chapter 8, your circadian clock is misaligned. To determine your personal amount of sleep needed, find a two-week period when you can afford to experiment, a period during which you’re not under any particular stress or deadlines and when you have free evenings—no late-night dinners.

go to sleep when you’re tired and wake up when you feel like waking up, without an alarm. Keep a log of your sleep and wake times. If, like most of us, you’ve been sleep-deprived for some time, you’ll need to pay back your sleep debt. Near the end of the two weeks, however, your body should have settled into a rhythm and you should be able to wake up without the alarm, feeling refreshed.

Treatment for hypersomnia involves slowly removing any prescription drugs that may be causing excessive sleepiness, avoiding alcohol, and resetting your sleep cycle. When that doesn’t work, modafinil or armodafinil upon awakening is generally safe, is tolerated well, and helps to maintain daytime wakefulness without causing jitters, nervousness, or sleep difficulties at night.

The American Academy of Sleep Medicine recommends the timed use of melatonin supplements to promote adaptation to new time zones or to help individuals having trouble sleeping for other reasons (such as age-related disturbances of the sleep-wake cycle). Melatonin taken in midafternoon (in conjunction with avoiding blue light) will advance the circadian clock, causing the body to think that nighttime has come early. The effect is somewhat mild, certainly not as powerful as a sleeping pill, but for many, this gentle nudging of the clocks is enough to promote sleep. As Johns Hopkins University sleep researcher Luis Buenaver says, “Your body produces melatonin naturally. It doesn’t make you sleep, but as melatonin levels rise in the evening it puts you into a state of quiet wakefulness that helps promote sleep.”

Melatonin levels in the blood are highest in young people (55–75 pg/ml) and start to decline after the age of forty, with the fastest decrease found from sixty years of age onward, reaching very low levels in the elderly (18–40 pg/ml). New research suggests that melatonin may have protective effects against many cancers, which may be part of the reason that as people age—and melatonin levels go down—they are more susceptible to cancers.