PDF Summary:Ageless, by Andrew Steele

Though we don’t like to think about it, we’re all going to get old. But in Ageless, physicist-turned-biologist Andrew Steele contends that aging isn’t as inevitable as it seems. Steele argues that we can treat—and even cure—aging. He explains that scientists are on the cusp of discovering anti-aging therapies and treatments that could lengthen the human lifespan and enable us to live many more years in good health, thus ensuring our health is no longer dependent on our chronological age.

In this guide, we’ll examine Steele’s explanations of the processes that make us grow sicker and slower as we age, the treatments you can expect to see in the future, and the scientifically proven steps you can take right now to slow your own aging process. We’ll also put Steele’s ideas into the context of the latest research in the field, and we’ll compare his predictions to those of other experts. (Spoiler alert: Steele is very optimistic about your chances of living a long and healthy life!)

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The potential fix: Steele explains that transplanting stem cells—a process called a bone marrow transplant or a hematopoietic stem cell (HSC) transplant—could replenish your supply of these versatile cells. Scientists have also learned to generate induced pluripotent stem cells (iPSCs), enabling mature cells (like your skin cells or blood cells) to turn into any cell type.

Pushing the Ball Back Up the Hill

In his 1957 book The Strategy of the Genes, developmental biologist Conrad Hal Waddington compares a stem cell to a ball rolling down a hill, its destination determined by the ridges and valleys—the genes—it encounters on the way down. Because they can reach any destination at the bottom of the hill, stem cells could treat aging by repairing any cell or tissue.

However, in practice, this is complex, and few treatments are ready. The only stem cell therapy currently approved for patients involves transplanting blood-forming stem cells from blood or bone marrow in people with blood cancers to replenish their supply of healthy blood cells.

The generation of iPSCs, another possibility Steele mentions, is also complex. It involves pushing the ball back up the hill and then letting it roll back down again. By introducing four genes into a mature cell, scientists can turn it into a pluripotent stem cell. This kind of stem cell usually only exists early in your development, when you’re just an embryo.

Scientists hope to use iPSCs to treat age-related diseases, restore damaged tissues, and grow new organs. The potential of these iPSCs may be limited, however, because they retain a memory of the kind of cell they were before, which restricts their effectiveness. So experts are working on ways to make iPSCs that are more like embryonic stem cells, without a memory—which might yield anti-aging treatments that use stem cells.

Your Immune System Becomes Less Capable

Your immune system, which protects you from infection, is another system that becomes less functional as you age, leading to a variety of harmful repercussions. Steele explains that this decline affects many components of your immune system.

1) Your thymus deteriorates. Your thymus is an organ that produces T cells, the white blood cells you need to fight infections. It begins to decline in volume and function when you’re a child and halves in size every 15 years.

The potential fix: Sterilization stops the thymus’s decline, but Steele points out that this isn’t a practical treatment. Growth hormones or gene therapy could rejuvenate the thymus, and scientists think it might be possible to use stem cells to grow a new thymus.

2) Cells that remember past infections impair your body’s ability to fight new infections. Steele explains that memory T cells and B cells become specialized to an infection. These cells—such as the ones specialized to fighting a common virus called cytomegalovirus (CMV)—remain in your immune system for years afterward. As you age, you have fewer T cells that aren’t specialized. The ones that are specialized use up resources and cause your immune system to fixate on old infections, making it less effective against new ones.

The potential fix: Steele writes that scientists could eliminate these single-minded cells via processes that kill senescent cells. Other ideas include targeting cells that have DNA damage or extending the telomeres of aging memory T cells and B cells.

3) Your immune system gets less efficient at finding and destroying tumors, which is why cancer is more prevalent in older people.

The potential fix: Steele explains that an HSC transplant could reboot your entire immune system and boost its performance at destroying cancerous cells—but wiping out and restarting the immune system poses a lot of risks.

Mustering (and Culling) the Forces

You can think of your immune system as your body’s military force, as T. Colin Campbell and Thomas M. Campbell explain in The China Study. White blood cells, like the T cells and B cells Steele mentions, attack invading bacteria and viruses. The thymus starts training T cells before you’re born and produces all of your T cells by the time you reach puberty. Then it declines and is replaced by fat—but some experts think that growth hormones can turn it back into a functional gland. One expert has even injected himself to test the idea, but it’s not proven that the process regenerates the thymus or kickstarts T cell production, expanding your defensive force.

If your T cells are limited in number, then why does Steele suggest killing some of them off? One reason is that when your T cells become specialized to fight off an invader like CMV, they leave your immune system with fewer unspecialized cells to fight other invaders. Worse, the T cells that remain look like senescent cells, with shortened telomeres and DNA damage. Experts contend that removing these cells might be best. But when it comes to CMV, experts don’t all agree that specialized T cells hurt you. In fact, there’s some evidence that CMV might strengthen your immune system by prompting it to send a more diverse population of T cells to fight a new infection.

Dysfunctional T cells might also be the reason the immune system sometimes fails to find tumors, which Steele notes happens more often with age. (T cells latch onto protein fragments called neoantigens on the surface of a cancer cell as they pass by. But T cells are only good at recognizing neoantigens if they’re densely concentrated, so they don’t detect a tumor if only a few of its cells have a suspicious neoantigen.) Other experts agree with Steele that a bone marrow transplant could reboot the immune system. But this isn’t a procedure that patients undertake lightly: They often have to spend several weeks in the hospital, and they’re highly susceptible to infection right afterward and remain at elevated risk for a year or more.

Your Microbiome Deteriorates

Finally, your microbiome—the unique array of bacteria, fungi, and viruses in your skin, mouth, and gut—is another complex system that falls out of balance as you age. Steele explains that an imbalance among the organisms in your microbiome leads to chronic inflammation throughout your body, damaging tissues and accelerating age-related changes.

The potential fix: Steele explains that probiotics (which contain live microorganisms) or prebiotics (which fuel beneficial microorganisms) rebalance the microbiome in favor of beneficial microbes. Probiotics and prebiotics can be combined into treatments called synbiotics. Or, a microbiome transplant, using purified fecal matter from a donor, can rebalance the microbiome.

Cultivating a Healthy Forest

Some scientists describe your microbiome as an ecological community within the larger ecosystem of your body—like a local forest with its own unique population of trees, birds, animals, and insects. Your microbiome contains trillions of microbes of thousands of different species. Some are helpful and some are harmful, and it’s important to maintain a balance. Experts say that reduced microbiome diversity correlates with frailty in older people. They’ve also found that, in middle age, a healthy microbiome gets increasingly unique, with a balance of microbes specific to you. Some experts assert that the more the composition of your microbiome changes as you age, the better it’s adjusted to your body and environment.

Steele contends that probiotics and prebiotics (and synbiotics, which combine the two) can benefit your microbiome’s ecological community. But some experts say that the evidence, particularly on prebiotics, is limited. Some physicians say that the average person doesn’t need to take prebiotics and would benefit more from eating a diet that’s rich in fiber, with generous helpings of vegetables and fruits. Additionally, some experts say that the research hasn’t shown probiotics to confer any benefits for people who are already healthy.

Aging Process #3: Structures and Signals Deteriorate

A third process key to aging is the deterioration of structures and signals within and between your cells, which Steele explains plays a role in many diseases and dysfunctions associated with aging. We’ll look at five structures and signals that do extensive damage as they deteriorate: telomeres, mitochondria, DNA, epigenetics, and communications between cells.

Telomeres Shorten

Telomeres are protective structures at the end of your chromosomes that prevent them from becoming frayed or tangled, but they get shorter as the cell divides repeatedly. Steele explains that telomeres help ensure your DNA replicates correctly when a cell divides. However, the machinery that completes this process can’t copy the full length of the chromosome, so the very end of the telomere is lost each time. Shortened telomeres appear in patients with diabetes, heart disease, reduced immunity, and cancer, and are associated with a higher risk of death.

The potential fix: Steele explains that an enzyme called telomerase might help. It’s disabled in most adult cells, and adding an extra copy of the telomerase gene helps a cell live on. But, he cautions that this might not be wise, since 90% of cancers turn telomerase back on (enabling cells to divide continuously). Other ideas include using gene therapy to lengthen telomeres directly, or employing telomerase activators (like a chemical called TA-65) to reactivate telomerase genes temporarily to reap the benefits of the enzyme without significantly increasing cancer risk.

Do Telomeres Live Up to the Hype?

In The Telomere Effect, biochemist Elizabeth Blackburn compares telomeres to aglets, the protective tips that keep shoelaces from fraying as they sustain wear and tear. In addition to ensuring all the critical information in your DNA gets copied properly, your telomeres help your body enforce the Hayflick limit: the number of times—usually 40 or 60—that each of your cells can divide. Once a cell divides enough times, the telomere becomes too short for the chromosome it protects to be replicated again, so the cell stops dividing.

When the link between a person’s age and the length of their telomeres was first discovered, some scientists (and many longevity enthusiasts) thought lengthening telomeres was the key to curing aging. After all, helping cells extend their telomeres offers a way around the Hayflick limit. This seemed even more promising because Blackburn discovered that in healthy cells, telomeres rebuild themselves with telomerase, which lengthens the strand of DNA before it gets copied. But it turns out that striking a balance is tricky: If telomerase is underactive, chromosomes shorten and cells die. But if telomerase is overactive, cancer risk is elevated.

While Steele suggests using gene therapy or compounds like TA-65 to lengthen telomeres, some experts consider the entire link between telomeres and longevity debunked. Recent research suggests that short telomeres and long telomeres both lead to problems. While short telomeres predispose people to immune system problems and degenerative diseases, long telomeres seem to increase a person’s risk of developing cancer and other disorders.

Mitochondria Become Less Efficient

Mitochondria, which generate energy within your cells, also deteriorate over time and cause aging in your brain, heart, and muscles. They become less plentiful and less efficient at producing energy in several ways. First, mitochondria contain their own chromosomes, and their DNA sustains damage and accumulates mutations. Second, when the process of generating power goes wrong, mitochondria produce reactive molecules called free radicals, which damage your proteins and DNA. And finally, dysfunctional mitochondria accumulate as your body gets less efficient at recycling them (and eventually play a role in Parkinson’s and Alzheimer’s).

The potential fix: Steele writes that antioxidants could protect mitochondria against free radical damage. Scientists could also develop drugs that enhance mitophagy, your body’s process for removing damaged and ineffective mitochondria. It might also be possible to reduce the effect of DNA mutations if scientists can insert a backup copy of mitochondrial genes, or use mitolytic drugs (which are currently hypothetical) to kill cells that no longer have functional mitochondria.

Powering Up Mitochondria

Scientists characterize mitochondria as the “powerhouses” of your cells. In The Vital Question, biochemist Nick Lane explains that our mitochondria descend from a hybrid of two single-celled organisms. That’s why mitochondria have their own DNA, which is subject to damage and mutations as you age. Scientists are working on ideas for keeping mitochondria healthy, but current approaches are experimental, and some experts are skeptical about the ideas Steele cites. For instance, he mentions the idea of inserting backup copies of mitochondrial DNA into the nucleus, an idea some experts think is so ambitious, it’s not practical to try.

Similarly, some experts say the “free radical theory of aging”—which Steele invokes when he suggests using antioxidants to protect mitochondria—has fallen out of favor. But others are returning to it after the discovery in 2023 of a compound that inhibits free radical production in mitochondria. While evidence suggests that taking large doses of antioxidants doesn’t stave off aging, some experts contend that this new compound can block free radicals without inhibiting mitochondria’s energy production. This advance—along with treatments that stimulate mitophagy—could bring us closer to keeping mitochondria young and healthy.

Your DNA Gets Damaged and Mutates

DNA damage (and the mutations that result from this damage) is another form of age-related deterioration—and one of the most difficult to fix, according to Steele. Each of your cells contains DNA, the genetic code for building and maintaining your body. This code is constantly damaged by toxins, carcinogens, and radiation—but most of all by the process of metabolizing food into energy. Your body can often repair the damage, but sometimes the repair process malfunctions and causes a mutation: a change to the instructions in your DNA. Mutations change how cells behave and can cause cancer or other consequences.

The potential fix: Steele writes that researchers could improve our natural DNA repair machinery, perhaps by adding or altering genes. They could also work to counter the effects of common DNA mutations, target the genes that enable mutated cells to make thousands of copies of themselves, or experiment with using stem cells to replace mutated cells.

Therapy for Your DNA

Your body is made of trillions of cells, and each contains your DNA. Many scientists agree with Steele that DNA’s susceptibility to damage and mutation is one of the most challenging problems of aging. But why do cells accumulate damage and mutations, despite having mechanisms that protect against these problems? Experts say that evolution made these safeguards just “good enough.” If a cell repaired all the damage, the energy costs would outweigh the benefits of the repairs.

Fortunately, scientists think that we can step in to repair some of the damage that our DNA accrues, like the gene therapy ideas that Steele cites. In The Gene, Siddhartha Mukherjee asserts that gene therapy—which uses genetic engineering to modify genes that are damaged or cause disease—could be the future of medicine. However, Mukherjee notes that progress has been slow, in part due to ethical concerns: Many scientists think that while it’s acceptable to use the primary tool of genetic engineering, CRISPR, to cure a disease in an individual, the tool shouldn’t be used to make changes to the genome,.because those changes, along with any unforeseen consequences, can be passed onto the next generation.

Epigenetics Get Less Effective at Controlling Your Genetic Code

Age-related deterioration also affects “epigenetics,” the chemical code that annotates your DNA and changes how genes are expressed. Steele writes that epigenetic annotations become less effective as you age—to the extent that epigenetic marks called DNA methylation predict your “epigenetic age.” If you have an epigenetic age lower than your chronological age, then you’re biologically younger, with better health and a lower risk of death. (Shortform note: DNA methylation decreases with age, so gene expression becomes less controlled as we get older.)

The potential fix: Steele explains that when scientists create iPSCs, restoring the ability of adult cells to turn into any cell type, the epigenetic age of these cells resets to zero. Because reprogramming your body’s cells into iPSCs would cause them to stop functioning as you need them to, scientists could reprogram cells temporarily, develop drugs that mimic some of the effects of reprogramming, or change chemical groups called “epigenetic marks” on your DNA.

Backing Up the Instructions

Because all of your cells carry your entire DNA, they need instructions to tell them what kind of cell they should become and what function they need to carry out. The epigenome provides this set of instructions via chemical groups called epigenetic marks. According to David Sinclair’s “Information Theory of Aging,” detailed in Lifespan, aging occurs due to the loss of these instructions. Sinclair has conducted research which he contends proves we can reverse aging by equipping cells with a backup copy of their original epigenetic instructions.

Additionally, Steele explains that we might treat epigenetic decline with two methods detailed earlier in the guide. First, epigenetic reprogramming—which Steele cites as a potential therapy for senescent cells—makes a cell’s epigenetic profile more youthful. This means that it could restore the flagging function of the epigenome. Second, generating iPSCs, detailed in the section on stem cells, rewinds mature cells’ epigenetic age to zero, which demonstrates the power of epigenetics to affect aging.

Communication Between Cells Goes Down

Finally, some contributors to aging don’t happen inside your cells, but instead involve the deterioration of the signals in the cells’ environment. Steele explains that signals constantly travel around your body: inflammatory signals, nutrient-sensing signals (which help you process nutrients), and signaling factors in blood. All of these signals become more dysfunctional as you age.

The potential fix: Steele explains that old blood cells can be rejuvenated by young blood. But because human trials of plasma transfusions from young donors haven’t yielded results, scientists are investigating alternatives such as plasmapheresis (a procedure that removes harmful substances from blood) and drugs that modulate the signaling factors in the blood.

Sending Mixed Signals

Other experts agree with Steele that many of the signals that travel between cells and systems become less functional with age. Experts say blood is a promising anti-aging target because it circulates around your body, carrying oxygen, nutrients, and compounds involved in the aging process. It also carries many of the signals that Steele cites as deteriorating as we age: Chemicals from your white blood cells are responsible for inflammation. That includes chronic inflammation, which occurs as levels of inflammatory substances become elevated and is considered a key part of aging by some scientists.

Steele also mentions the idea of rejuvenating old blood with plasmapheresis, drug treatments, or transfusions of young blood—a method that hasn’t yielded results. But that hasn’t stopped people from trying: Venture capitalist Bryan Johnson has made headlines for taking more than 100 supplements a day, completing strenuous workouts, eating a strict diet that leaves him hungry most of the time, doing extensive medical testing—and undergoing blood-plasma transfusions from his teenage son. He stopped the transfusions after finding that they didn’t make a difference, and the FDA has warned that such infusions aren’t safe or effective.

Do Scientists Have Any Other Ideas for Slowing Down or Preventing Aging?

Many of the causes of aging that scientists have investigated are isolated to specific kinds of cells or to one part of the body. But Steele writes that we need a more holistic approach to learn how aging works and how to cure it. By looking at human biology as a system, scientists will be able to build predictive models that show how all of the components work together.

(Shortform note: When Steele talks about building predictive models of human biology, he’s talking about using vast amounts of experimental data to build models of biological systems like the human body. These models can be used to make predictions about the results of new experiments. While some scientists warn that we can’t rely on computational models to replace experiments, others predict that a model accounting for all of the systems in the human body and how they interact could change how scientists do research and develop new treatments.)

In addition to learning about human biology as a system, Steele contends that we may need to learn to modify our genes. He explains that genes seem to be responsible for only 10% of our longevity. But by studying people who have lived extraordinarily long lives, researchers could identify longevity-related genes and develop drugs to mimic their effects. Scientists could also use genetic therapy to modify our DNA by adding, replacing, or removing genes.

(Shortform note: Scientists’ estimates of how much of our longevity is genetic range from under 10% to about 25%. Which genes influence lifespan, and how, isn’t yet known. But some experts think you can be your own genetic engineer by making lifestyle choices—exercising more, managing stress better, and eating a healthier diet—that prompt your body to turn off genes that promote aging and turn on genes that fight it. Even if your genes decide 25% of your health outcomes, that leaves 75% to be affected by other factors.)

How Can We Prevent Aging With What We Know Right Now?

We’ve discussed the advances that Steele writes may be able to delay or prevent aging in the future. Though much of that science is still in the research stage, he writes that scientists already have enough evidence to know there are things you can do right now to increase your chances of living a long and healthy life. Much of the advice in this section—like eating a balanced diet or brushing your teeth—won’t sound novel. But Steele points out that we already have evidence that these measures are effective at keeping us fit and healthy as we age.

Quit Smoking and Stop Living a Sedentary Lifestyle

The first change to make is to quit if you currently smoke. Smoking increases your risk of cancer, induces DNA mutations, and causes chronic inflammation linked to cardiovascular disease. Steele explains that while smoking reduces lifespan by 10 years, quitting at age 30 restores life expectancy to normal.

(Shortform note: The consensus is strong: Smoking is one of the most unhealthy habits. While many of us know someone who’s been a lifelong smoker yet is still in good health, experts think such people have very unusual genetics, and nobody should keep smoking. Research also suggests it’s never too late to benefit from stopping smoking.)

A second change that can impact your health is shifting from a sedentary lifestyle to a routine with daily exercise. That change reduces your risk of death and disease, boosts your metabolism, improves the condition of your muscles and bones, and reduces inflammation.

(Shortform note: As Steele explains, regular exercise comes with major health benefits, and decades of studies show that aerobic exercise can lengthen your life. You don’t have to run marathons to benefit, either. In “Blue Zones”—places like Okinawa, Japan and Ikaria, Greece where rates of chronic disease are lower and life expectancies are higher—people naturally exercise by walking to work, climbing stairs, and doing active chores like gardening.)

Eat a Balanced Diet, But Skip the Vitamins

Another significant lifestyle choice is your diet. Steele explains that while it’s difficult to conduct rigorous research, the healthiest option seems to be to eat a balanced diet of different foods, without an excess of sugar, fat, or alcohol. Eating less meat and more fruit and vegetables may improve health, according to Steele, and he contends that losing excess weight might reduce your risk of disease. Additionally, he notes that evidence does not support the efficacy of vitamins and supplements (unless you have a nutritional deficiency). Similarly, Steele advises against taking longevity drugs: We don’t yet have evidence that the options available actually work.

Finding the Right Diet

Choosing a healthy diet sounds simple enough, but what does it really entail? A few proven strategies include cutting processed meat, eating dark-colored fruits and vegetables, and skipping processed foods and beverages. Taking a healthy approach to weight can also help: Some experts say that the variations in weight that go with “yo-yo dieting” are worse for your body than maintaining a stable weight. You might shift your focus from losing weight to eating a diet that emphasizes healthy foods (like vegetables, fruits, tree nuts, and yogurt) and limits starchy foods and junk foods (which are high in fat, sugar, or salt but low on healthy nutrients).

Additionally, Steele isn’t the only scientist to advise against supplements. In In Defense of Food, Michael Pollan writes that research has shown little to no benefit in taking supplements each day. (Yet Pollan does recommend taking a multivitamin and fish oil after age 50 to offset your body’s declining ability to absorb nutrients.) In How Not to Die, Michael Greger explains that ideally, all of the nutrients your body needs would come from whole foods. There’s one caveat: If you’re eating a plant-based diet, you might need to supplement it. It might be wise to consult with a nutritionist to be sure, as Tim Ferriss advises in The 4-Hour Body.

Brush Your Teeth and Get Enough Sleep

Steele writes that it’s also important to brush your teeth twice daily with fluoride toothpaste and clean between your teeth, which impacts the population of bacteria in your mouth. These bacteria contribute to gum disease and to diseases throughout your body via chronic inflammation.

(Shortform note: Experts agree that your dental health influences the rest of your body, as your mouth is the entry to your digestive and respiratory tracts. The harmful bacteria involved in tooth decay and gum disease contribute to cardiovascular disease and pneumonia.)

Another important lifestyle choice is the amount of sleep you get. Steele writes that sleeping at least seven hours every night, but not more than eight hours, reduces your risk of death and enables your brain to flush out amyloids.

(Shortform note: Experts agree that good sleep is as crucial as diet and exercise. As you sleep, your body repairs damage and your brain flushes out toxins. In Why We Sleep, Matthew Walker explains that your brain also secures memories for long-term recall and clears short-term memory, which prepares you to learn, remember, and concentrate. Experts say adults need seven to nine hours of sleep each night: You might need more than eight hours if your sleep need is higher, you’re catching up on sleep, or you’re sick.)

Take Precautions Against Infectious Disease and Watch Your Cardiovascular Health

Evidence is overwhelmingly in favor of taking precautions against infectious disease. Steele advises keeping up with vaccinations, washing your hands, cooking food thoroughly, and staying home if you’re unwell. This can protect you in the short term by preventing infection and in the long term by reducing chronic inflammation.

(Shortform note: Preventing infection is common sense: Nobody wants to spend a week sick in bed nor to develop chronic inflammation or post-viral symptoms. Even common viruses can have debilitating long-term effects. An example is “long Covid,” which increases the risk of heart, lung, liver, and kidney problems or dementia.)

Steele also recommends monitoring your cardiovascular system. He writes that regularly measuring your blood pressure and heart rate can help you keep an eye out for signals you need to lose weight, get more exercise, improve your diet, or talk to your doctor.

(Shortform note: Experts agree that blood pressure and heart rate are two vital signs to watch. Your blood pressure is the force with which your blood pushes against the walls of your arteries. Your heart rate is the number of times your heart beats each minute. Tracking them can help safeguard your health: In Outlive, Peter Attia contends that the key to avoiding decline is to prevent four chronic diseases—heart disease, cancer, neurodegenerative disease, and type 2 diabetes.)

Protect Your Skin From Sun Exposure

Finally, Steele advises that you protect your skin from the sun by wearing sunscreen, avoiding exposure when the sun is high, and blocking sunlight with clothing. This prevents the DNA damage that occurs when UV light breaks bonds between molecules. When your body repairs this damage incorrectly, mutations occur and cancer risk increases.

(Shortform note: Experts say UV exposure increases your risk of skin cancer and cataracts, and causes your skin to age prematurely. They estimate that sun exposure is responsible for up to 80% of wrinkles, brown spots, texture changes, and visible blood vessels. Sunscreen slows these signs of aging.)

An Often-Overlooked Anti-Aging Strategy

One proven method for protecting your health as you age that Steele doesn’t mention is maintaining strong relationships with other people. Strong social connections protect your health and can have a profound impact on your longevity. If you have social relationships that help you feel a sense of belonging, those social bonds can prevent serious illnesses, improve your ability to cope with anxiety and depression, and help you to live a healthier lifestyle.

As you’re weighing Steele’s recommendations and strategies, it might also help to keep in mind that a healthy lifestyle isn’t an all-or-nothing endeavor. Some experts note that when you’re trying to motivate yourself to make healthier decisions, the aggregate of your choices matters more than trying to behave perfectly. Small decisions accumulate and are significant in the long run.

This might be particularly encouraging if you’re impatiently waiting for the high-tech anti-aging advances that Steele describes to materialize: You might not yet be able to pop a pill that promises to help you live to 120, but you can make many smaller decisions that meaningfully impact your chances of living a long and healthy life.