Lifespan. David Sinclair
Читать онлайн книгу.call what happens to us a “loss of resilience,” and we generally have accepted it as part of the human condition.
There is nothing more dangerous to us than age. Yet we have conceded its power over us. And we have turned our fight for better health in other directions.
WHACK-A-MOLE MEDICINE
There are three large hospitals within a few minutes walk of my office. Brigham and Women’s Hospital, Beth Israel Deaconess Medical Center, and Boston Children’s Hospital are focused on different patient populations and medical specialties, but they’re all set up the same way.
If we were to take a walk into the lobby of Brigham and Women’s and head over to the sign by the elevator, we’d get a lay of this nearly universal medical landscape. On the first floor is wound care. Second floor: orthopedics. Third floor: gynecology and obstetrics. Fourth floor: pulmonary care.
At Boston Children’s, the different medical specialties are similarly separated, though they are labeled in a way more befitting the young patients at this amazing hospital. Follow the signs with the boats for psychiatry. The flowers will take you to the cystic fibrosis center. The fish will get you to immunology.
And now over to Beth Israel. This way to the cancer center. That way to dermatology. Over here for infectious diseases.
The research centers that surround these three hospitals are set up in much the same way. In one lab you’ll find researchers working to cure cancer. In another they’re fighting diabetes. In yet another they’re working on heart disease. Sure, there are geriatricians, but they almost always take care of the already sick, thirty years too late. They treat the aged—not the aging. No wonder so few doctors today are choosing to specialize in this area of medicine.
There’s a reason why hospitals and research institutions are organized in this way. Most of our modern medical culture has been built to address medical problems one by one—a segregation that owes itself in no small part to our obsession with classifying the specific pathologies leading to death.
There was nothing wrong with this setup when it was established hundreds of years ago. And by and large, it still works today. But what this approach ignores is that stopping the progression of one disease doesn’t make it any less likely that a person will die of another. Sometimes, in fact, the treatment for one disease can be an aggravating factor for another. Chemotherapy can cure some forms of cancer, for instance, but it also makes people’s bodies more susceptible to other forms of cancer. And as we learned in the case of my grandmother Vera, something as seemingly routine as orthopedic surgery can make patients more susceptible to heart failure.
Because the stakes are so exceptionally high for the individual patients being treated in these places, a lot of people don’t recognize that a battle won on any of these individual fronts won’t make much of a difference against the Law of Human Mortality. Surviving cancer or heart disease doesn’t substantially increase the average human lifespan, it just decreases the odds of dying of cancer or heart disease.
The way doctors treat illness today “is simple,” wrote S. Jay Olshansky, a demographer at the University of Illinois. “As soon as a disease appears, attack that disease as if nothing else is present; beat the disease down, and once you succeed, push the patient out the door until he or she faces the next challenge; then beat that one down. Repeat until failure.”100
The United States spends hundreds of billions of dollars each year fighting cardiovascular disease.101 But if we could stop all cardiovascular disease—every single case, all at once—we wouldn’t add many years to the average lifespan; the gain would be just 1.5 years. The same is true for cancer; stopping all forms of that scourge would give us just 2.1 more years of life on average, because all other causes of death still increase exponentially. We’re still aging, after all.
Aging in its final stages is nothing like a bushwalk, where a bit of rest, a drink of water, a nutritional bar, and some fresh socks can get you another dozen miles before sunset. It’s more like a fast sprint over an ever-higher and ever-closer set of hurdles. One of those hurdles will eventually send you for a tumble. And once you’ve fallen one time, if you do get up, the odds of falling again just keep getting higher. Take away one hurdle, and the path forward is really no less precarious. That’s why the current solutions, which are focused on curing individual diseases, are both very expensive and very ineffective when it comes to making big advances in prolonging our healthspans. What we need are medicines that knock down all the hurdles.
WHY TREATING ONE DISEASE AT A TIME HAS LITTLE IMPACT ON LIFESPAN. The graph shows an exponential increase in disease as each year passes after the age of 20. It’s hard to appreciate exponential graphs. If I were to draw this graph with a linear Y-axis, it would be two stories tall. What this means is your chance of developing a lethal disease increases by a thousandfold between the ages of 20 and 70, so preventing one disease makes little difference to lifespan.
Source: Adapted from A. Zenin, Y. Tsepilov, S. Sharapov, et al., “Identification of 12 Genetic Loci Associated with Human Healthspan,” Communications Biology 2 (January 2019).
Thanks to statins, triple-bypass surgeries, defibrillators, transplants, and other medical interventions, our hearts are staying alive longer than ever. But we haven’t been nearly so attentive to our other organs, including the most important one of all: our brains. The result is that more of us are spending more years suffering from brain-related maladies, such as dementia.
Eileen Crimmins, who studies health, mortality, and global aging at the University of Southern California, has observed that even though average lifespans in the United States have increased in recent decades, our healthspans have not kept up. “We have reduced mortality more than we prevented morbidity,” she wrote in 2015.102
So prevalent is the combined problem of early mortality and morbidity that there is a statistic for it: the disability-adjusted life year, or DALY, which measures the years of life lost from both premature death and poor state of health. The Russian DALY is the highest in Europe, with twenty-five lost years of healthy life per person. In Israel, it is an impressive ten years. In the United States, the number is a dismal twenty-three.103
The average age of death can vary rather significantly over time, and is affected by many factors, including the prevalence of obesity, sedentary lifestyles, and drug overdoses. Similarly, the very idea of poor health is both subjective and measured differently from place to place, and so researchers are divided on whether the DALY is rising or declining in the United States. But even the more optimistic assessments suggest that the numbers have largely been static in recent years. To me, that in itself is an indictment of the US system; like other advanced countries, we should be making tremendous progress toward reducing the DALY and other measures of morbidity, yet, at best, it seems we’re treading water. We need a new approach.
It doesn’t take studies and statistics to know what’s happening, though. It’s all around us, and the older we get, the more obvious it becomes. We get to 50 and begin to notice we look like our parents, with graying hair and an increasing number of wrinkles. We get to 65, and if we haven’t faced some form of disease or disability yet, we consider ourselves fortunate. If we’re still around at 80, we are almost guaranteed to be combating an ailment that has made life harder, less comfortable, and less joyful. One study found that 85-year-old men are diagnosed with an average of four different diseases, with women of that age suffering from five. Heart disease and cancer. Arthritis and Alzheimer’s. Kidney disease and diabetes. Most patients have several additional undiagnosed diseases, including hypertension, ischemic heart disease, atrial fibrillation, and dementia.104 Yes, these are different ailments with different pathologies, studied in different buildings at the National Institutes of Health and in different departments within universities.
But aging is a risk factor for all of them.
In
100
Have we made a deal with the medical devil that’s backfired? Olshansky certainly thinks so, contrasting the quest for human longevity and health to the dark narrative of Faust’s ultimately pyrrhic deal with Mephistopheles. “It’s possible that humanity has squeezed about as much healthy life out of public health interventions as possible and that the human body is now running up against inherent limits that the genetically fixed attributes of our biology impose.” S. J. Olshansky, “The Future of Health,”
101
The numbers are indeed staggering: close to 800,000 Americans die annually of cardiovascular-related diseases; medical costs related to cardiovascular issues are expected to be over $818 billion by 2030 and lost productivity costs above $275 billion. “Heart Disease and Stroke Cost America Nearly $1 Billion a Day in Medical Costs, Lost Productivity,” CDC Foundation, April 29, 2015, https://www.cdcfoundation.org/pr/2015/heart-disease-and-stroke-cost-america-nearly-1-billion-day-medical-costs-lost-productivity.
102
As treatments for patients with disease have prolonged their lives, so the amount of disease in society has augmented. This situation means that the only way to increase the human healthspan will be by “‘delaying aging,’ or delaying the physiological change that results in disease and disability,” the author argues. Along with scientific breakthroughs, changes in socioeconomic inequalities, lifestyle, and behavior can contribute to improving both healthspan and lifespan. E. M. Crimmins, “Lifespan and Healthspan: Past, Present, and Promise,”
103
According to the World Health Organization, one DALY can be thought of as one lost year of “healthy” life. The sum of these DALYs across the population, or the burden of disease, can be thought of as a measurement of the gap between current health status and an ideal health situation in which the entire population lives to an advanced age, free of disease and disability. “Metrics: Disability-Adjusted Life Year (DALY),” World Health Organization, https://www.who.int/healthinfo/global_burden_disease/metrics_daly/en/.
104
And almost everyone at that age spends a considerable part of his or her life visiting the doctor. According to the study, published in 2009 by the