Abstract
In the past century, the average duration of life of people living in developed countries rose by 30 years. Most of this gain was a result of advances in public health that saved the young by warding off communicable diseases. However, in the latter half of the 20th century, improvements in lifestyle modification and advances in biomedical technology enabled people at middle and older ages to experience extended lives. Thus, aging as we know it today is a new phenomenon—experienced by a small but rapidly growing segment of our world. As appealing as our longer lives may be, there was a price to pay for life extension—the rise of noncommunicable fatal and disabling diseases. It was a fair exchange, but now humanity is left with the difficult task of dealing with this Faustian trade. A new approach to public health in a rapidly aging world has been proposed (the longevity dividend), with the idea that extending healthy life by slowing aging may prove to be the most efficient way to combat the fatal and disabling diseases that plague us today. Here, I articulate the case for why we now need to turn our attention to combating aging itself.
‘The benefits of most public health interventions that are now well established and the recognized harmful health consequences of some behavioral risk factors were rarely considered as accepted doctrine when first identified.’
Life expectancy increased dramatically since the beginning of the 20th century: in most developed nations, people can now expect to live decades longer than their ancestors did just 3 or 4 generations ago. Most of the rise in longevity was driven by basic advances in public health and improved nutrition, but more recently, improved behavioral risk factors or lifestyle choices (eg, reduced smoking) and treatments for specific diseases have extended life further. Challenges to rising life expectancy have also emerged: the global pandemic of adult and childhood onset obesity and the resurgence of some lethal and disabling infectious diseases among them.
More recent declines in death rates in the past quarter century, especially at middle and older ages, are largely a product of a successful “disease model” in which physicians and scientists have found ways to delay the onset and progression of fatal diseases or extend the lives of those who have them. The contemporary disease model is an outgrowth of the approach to infectious diseases that arose centuries ago, in which each disorder is treated as it arises, as if it were independent of all other conditions.
The longer lives we now enjoy have come with both desirable and undesirable side effects. On the positive side, healthy life spans have risen rapidly for many during the past century, offering unique opportunities to individuals and societies to benefit from many more healthy, active, and productive years than ever before in history. 1 In fact, my colleagues and I have demonstrated that even in the oldest region of the life span in the United States today (those aged 85+ years), there are a surprisingly large percentage of people who are in nearly perfect mental and physical health, living their lives in large measure as if they were decades younger. 2 In addition, the absolute number of healthy older people will rise rapidly in the coming decades because of upward shifts in age structure, and there is reason to be optimistic that the healthy lifestyles adhered to by many when they were younger will pay off in the coming decades in the form of even further extensions of healthy life.
However, a Faustian trade—the rise of chronic fatal and disabling conditions at unprecedented rates in recent decades—also accompanies our longer lives. One should keep in mind that children saved from dying of communicable diseases that killed many before the age of 10 years throughout human history now live long enough to experience the complications that accompany aging bodies. Few would argue against such a trade, but the fact that it occurred is undeniable. Whereas the good news is that a much longer portion of our total life spans are lived in relatively good health, the rise of cardiovascular disease, cancer, Alzheimer’s, and a host of other conditions are largely a product of living long enough to experience them. Further life extension will no doubt accelerate growth in the prevalence of aging-related fatal and disabling conditions, and variation in lifestyle and genetics guarantees that disparities in health, quality, and duration of life will remain a part of our aging landscape. Nevertheless, there is still plenty of room for lifestyle medicine to have a significant positive impact on the health of our population in the coming decades.
A New Paradigm of Health Promotion and Disease Prevention for the 21st Century
The benefits of most public health interventions that are now well established and the recognized harmful health consequences of some behavioral risk factors were rarely considered as accepted doctrine when first identified. In fact, some unassailable public health interventions today are not only still rejected by some, but almost every major discovery in the history of public health initially faced disbelief, vehement skepticism, and even scorn. What I want to emphasize in this essay is that the scientific study of aging is now leading us in the direction of a major breakthrough that has the potential to revolutionize public health in our aging world. Obstacles once again stand in the way.
Here, I will describe the Longevity Dividend Initiative (a contemporary effort to extend the period of healthy life by slowing the biological processes of aging) 3 and some of the obstacles that stand in the way of what many consider to be one of the most exciting breakthroughs in the history of science and public health. The concept of the Longevity Dividend should be thought of as a supplement to lifestyle medicine approaches to public health that have a long history of success and that still offer plenty of room to improve health and duration of life for most.
Healthy Life Extension
The most precious of all commodities is life itself, and if there is one attribute most of us share, it is the desire to remain alive. The yearning for healthy life is equally important, perhaps more so, especially for those struggling to regain health that has been lost. One would think, therefore, that the case for extending our healthy years would be universally accepted and easy to make, regardless of how it is achieved. Sadly, this is not the case.
In public health, examples of interventions that in the past had a profound influence on the length and quality of life include the development and dissemination of clean water, sanitation, indoor living and working environments, and refrigeration. During the past century, epidemiologists made the public aware of the life-shortening effects of smoking and other harmful risk factors and the life-extending effects of proper diet and exercise, among others.
In the modern world of medicine and medical technology, trips to the doctor, dentist, or other health professional are justified today as forms of primary prevention. When a health issue arises, such as a serious infection, cancer, or heart disease, it is now routine to seek out and trust modern medical treatment as the best approach to regaining one’s health. In fact, a strong endorsement for the efficacy of medicine’s ability to extend healthy life comes from its validation by the insurance industry.
These 3 pillars of healthy life extension have earned our trust, and deservedly so, but now concerns are being raised about how much more healthy life can be manufactured using these approaches. The reason is the biological aging of our bodies.
In the past half century, a combination of public health and medicine enabled most people born in the developed world to live past 65 years, and for them, a large percentage live past the age of 85 years. As appealing as this is, the problem that arises with extended survival is that a less tractable risk factor has emerged—the biological aging of our bodies. Public health can manufacture only so much survival time through lifestyle modification, after which medical technology has an important life-extending impact; but even these methods of life extension eventually lead the survivors to face the increased and accelerated ravages of the biological aging of our bodies.
Think of the effect of aging on the body as the same as the effect of miles on your car. Very few things go wrong with most cars during the first 3 years and 36 thousand miles, and for some automobiles. the warranty period has been extended to 10 years and 100 000 miles. Operate these cars beyond their warranty period, and a cluster of problems emerges. These problems are an inevitable by-product of the passage of time and the accumulation of damage that arises from operating the machine—they are not programmed to occur at a set time by the auto manufacturers. Although planned obsolescence is part of the manufacturing ethos for some manufacturers of certain products, what I mean here is that a specific “death time” is not built into a car.
The same principles hold true for human bodies. Once we operate our bodies beyond the equivalent of their biological warranty period, a large number of health issues begin to emerge and cluster tightly into later regions of the life span. Among scientists who track these events, this is known as competing causes, which is another way of saying that a large number of lethal and disabling conditions accumulate in aging bodies. Ameliorating any 1 lethal condition independent of all others leaves the person with a remaining high risk from all other remaining conditions. With time (and age), the treatments devised through medicine (that tend to focus on 1 disease at a time) and risk factor modification then become progressively less effective as survivors move further into older age windows where aging-related diseases cluster ever more tightly together. Keep in mind that just like automobiles, our bodies are not programmed with aging or death genes that are set off at a predetermined age. Aging is best thought of as an inadvertent by-product of fixed genetic programs that evolved under the direct force of natural selection for early life developmental events: aging is a product of evolutionary neglect, not evolutionary intent.
Recognizing the fact that competing causes places a damper on the future effectiveness of medical interventions that are disease oriented, scientists in the field of aging have proposed that the next big step in public health and healthy life extension is to attack the seeds of aging rather than just its consequences, as we do now. The idea is to slow the aging of our bodies such that 1 year of clock time is matched by less than 1 year of biological time. In this way, we would retain our youthful vigor for a longer time period and, if delayed aging interventions work the way we hope they do, experience a compression of the infirmities of old age into a shorter time frame at the end of life. Delaying the biological aging of our bodies is the only viable approach to addressing the increasing importance of competing causes and the rise of aging as an ever more important risk factor for disease. This effort to transform aging science into a new paradigm for combating disease and extending the period of healthy life is referred to as the Longevity Dividend Initiative. 4
It is at this juncture where one of the main problems occurs. The contemporary proposal to slow aging as a means to extend healthy life has historical linkages to medical deception, charlatanism, and greed. 5 Historically, the quest for immortality was couched within a “prolongevity” message suggesting that ingesting or injecting substances with alleged antiaging properties could manufacture youth. One of the most famous among these is the alchemist’s dream to transmute lead into gold, which was thought to confer properties of immortality to those who ingested minute quantities.
In the late 19th century, the French physiologist Charles-Edouard Brown-Sequard claimed to have discovered the secret to rejuvenation. Brown-Sequard crushed the testicles of domesticated animals, extracted “vital” substances from them, and then inoculated older people against the “aging disease.” Modern versions of these ancient antiaging potions were described by the US Government Accounting Office as posing the “potential for physical and economic harm.” 6
Finally, some scientists in the field of aging have formed companies designed to attract outside investors interested in cashing in on a possible breakthrough in the field of aging. 7 Although this approach enables some aging science to occur that would not otherwise be funded, it can and has led to exaggerated claims and unproven interventions that reach the marketplace before they are fully evaluated using the tools of science. This too creates suspicion among the public who already have a difficult time distinguishing between medical fraud and genuine public health interventions.
Taken together, these historical and contemporary roadblocks to legitimacy have delayed the entrance of aging science into the realm of accepted discourse as a legitimate and, quite frankly, valuable and needed public health intervention. However, these are not the only roadblocks.
Religious Arguments
Religious objections are sometimes posed in response to proposals to enhance public health by modulation of aging. The objection usually starts from the assertion that tampering with aging is equivalent to tampering with god’s plan for us—an effort that should not be pursued. However, this argument loses its power when those proposing it admit that both they and their children have been vaccinated against lethal childhood diseases. It is hard to imagine that god’s plan is to kill most children from communicable diseases before reaching the age of 10 years, but up until the 19th century that was humanity’s fate. Most people who make this argument also admit that they would seek medical attention if they (or their loved ones) experience heart disease or cancer. Why is one form of disease prevention acceptable, whereas another is not?
Population Growth
When delayed aging was first proposed as a public health intervention in the 1950s, rapid population growth was a concern because the growth rate (GR) in the post–World War II era was about 3%. To place this GR into perspective, at that rate, it takes the population 26 years to double in size. Thus, there was reason to be concerned about the population GR during most of the last half of the 20th century; this was alarming to both demographers and environmentalists. Although the rate of population growth has attenuated considerably since 1950, the momentum for population growth will remain with us through the middle of this century. However, environmental concerns have escalated considerably. Population growth and resource depletion should be on our minds, and these are issues that are appropriate to raise when having a discussion about healthy life extension.
The thing is, those making this argument believe that delayed aging will dramatically accelerate population growth, wipe out the reductions in the GR achieved in recent decades, further challenge resource depletion, and generate a new set of population and environmental headaches. As it turns out, none of these concerns is valid.
With regard to population growth, I have estimated how the GR would change with the hypothetical extreme scenario of immortality (ie, no more deaths; table 1 in Olshansky 8 ). Under the extreme scenario of immortality, the GR would be about 1.5% (ie, the GR would be defined by the birth rate because the death rate would be zero), which is 3 times faster than the current GR of about 0.5%. However, longer lives tend to be accompanied by lower fertility, so I estimate a GR under conditions of hypothetical immortality of about 0.9%—still twice the current GR. Because immortality is not likely to happen any time soon and because the longevity dividend associated with delayed aging would yield only marginal increases in life expectancy, the actual population GR would only rise slightly if the Longevity Dividend is achieved.
In fact, the population GR would also rise marginally with a hypothetical cure for cancer or heart disease. I have yet to hear anyone argue that cures for these diseases should not be pursued because success would be accompanied by accelerated population growth and resource depletion. The bottom line is that the Longevity Dividend Initiative will have a negligible effect on population growth and the environment, but it will have a dramatically positive impact on work, retirement, health care financing and costs, and physical and psychological well-being. 9
Delayed Aging Means Increased Infirmity
Perhaps the most common misconception and fear about aging science and the Longevity Dividend Initiative is the belief that delayed aging will extend the period of infirmity at the end of life—the fear that most people have as they approach older ages. There is an irony to this view because although there may be disagreements among the scientists involved on exactly how to accomplish the goals we have set, the one thing we all have in common is the final and most important goal of extending the period of healthy life. An intervention that does not meet the test of extending the health and functionality of both body and mind together would not be pursued—in fact, such an intervention would be seen as harmful.
Articulating the Case for the Longevity Dividend
The case for the Longevity Dividend is extremely compelling and, in theory, should be easy to make to funders, public health professionals, and the general public. Here is the line of reasoning: (1) treating diseases worked well in the past to extend healthy life, but aging has emerged as the primary risk factor for the most common fatal and disabling diseases; (2) the longer we live, the greater the influence of aging on disease expression; (3) aging science offers medicine and public health a new and potentially far more effective weapon for preventing disease, extending healthy life, and avoiding the infirmities associated with old age4,10; (4) failing to take this new approach could leave people who reach older ages in the future even more vulnerable to rising disability than they are now; (5) aging science represents a new paradigm of public health that will lead to more effective methods of delaying most fatal and disabling diseases, extending healthy life, and reducing the prevalence of infirmities more commonly experienced at older ages.11-13
Language used to describe the Longevity Dividend must be unambiguous. Much like the introduction of antibiotics in the mid-20th century and the broad dissemination of basic measures of public health a century ago, humanity is once again fortunate enough to witness the rise of a new paradigm in human health. Aging science has successfully turned the spotlight on the origins of our aging bodies and minds and the fatal and disabling diseases that accompany us in our later years. What the scientific study of aging reveals shakes up a long-held assumption that aging is an inevitable and immutable by-product of the passage of time, 14 and these new discoveries fundamentally challenge the fatalist view that aging and death are nature’s way of removing the old to make way for the young.
Science has now demonstrated that aging is inherently modifiable. Furthermore, there is now reason to believe that aging science can be translated into new, more effective medical and public health interventions that will be able to combat fatal and disabling diseases far more effectively than any intervention available today, yielding an extension of the period of healthy life in ways that could not even be conceived of just a few years ago.
Although people who benefit from advances in aging science will probably live longer, it is the extension of healthy life that is the primary goal, along with reductions in the infirmities of old age and increased economic value to individuals and societies that would accrue from the extension of healthy life. These goals and ideals for extending healthy life match perfectly the outcomes that are being pursued through lifestyle medicine.
It is only a matter of time before aging science acquires the same level of prestige and confidence that medicine and public health now enjoy, and when that time comes, a new era in human health will emerge. There are an abundance of formidable obstacles standing in the way, including strongly held views of how to proceed, a history of association with dubious aging interventions, and misconceptions about the goals in mind and the impact of success on population growth and the environment. Once the air clears and aging science is translated into effective and safe interventions that can be measured and documented to extend our healthy years, the 21st century will bear witness to one of the most important new developments in the history of medicine.
Footnotes
Acknowledgements
Author’s Note
This article is based on a talk delivered at the American College of Lifestyle Medicine 2013 Annual Meeting, October 2013.