A New Book Examines Why and How We Age
Humans are living longer than ever before, and Caleb Finch, professor of gerontology and biological sciences at the University of Southern California, has spent his scientific career trying to explain why. Finch, a leading researcher on aging and longevity, studies the forces that cause people to grow old, get sick, and die. Finch's new book, The Biology of Human Longevity: Inflammation, Nutrition, and Aging in the Evolution of Lifespans, synthesizes 10 years of research, defining new connections among inflammation, nutrition, and the diseases that come with advanced age.
How has the human life span changed over time?
In the last 200 years, one year of extra lifespan has been added for about every four years of historical time. Life expectancy has doubled since the industrial revolution, from about 40 years to near 80 years.
The same factors that increased lifespan in modern times were also responsible for increasing human lifespans in evolution. Life expectancy doubled from 20 years in our great ape ancestors, to 40 years, which was the general human life expectancy before the modern era.
Why are humans living so much longer now than ever before?
Aging processes in humans are directly related to the nutritional and inflammatory aspects of the environment. One example is Alzheimer's disease: Research from our lab has shown that the senile plaques that build up in that disease are related to inflammatory processes in the brain. And we now know that inflammation intensifies atherosclerosis, the hardening of the arteries that can contribute to stroke and heart attack.
Longer life spans have been a worldwide phenomenon associated with improvements in hygiene and medical care and reductions in infectious disease. Some have explained this through the reduction of infant mortality. But we're also living longer because we're staying healthier—kids have fewer infectious diseases to fight with. This reduction of inflammation and infection, along with the improvement of nutrition, has contributed to longevity by slowing many of the diseases of aging.
What is inflammation, and how does it impact health?
Inflammation comes from two major sources. The first is chronic infections, which have been reduced for most of us by advances in medical treatment. And of course, some infections we can't avoid. The second source of inflammation is the environment—what we breathe and what we eat. Obesity, for example, is a pro-inflammatory state. Fat tissues secrete inflammatory molecules called cytokines, which contribute to chronic inflammation and conditions like heart disease and diabetes. Environmental pollutants such as cigarette smoking and air pollution are linked to vascular and lung diseases. The point is that the environment governs the progress of a number of the diseases of aging, such as atherosclerosis, cancer, and Alzheimer's.
What can people do to stay healthy and live longer?
Exercise and maintaining a healthy weight—both of which have anti-inflammatory effects—are remarkably preventive for all the diseases of aging. This cuts across all the systems. What's good for your heart is good for your brain and is good for preventing cancer. The separate diseases of adult life are much more related to each other and to overall health than we previously recognized.
Research on mice, flies, and other animal models has shown that following an extremely low-calorie diet can increase their life span by as much as 35 percent. Does this mean that people could extend their lives by eating less?
This is being addressed right now in various studies of human volunteers. One thing is clear; if you are obese and diabetic, then exercise and diet are really important. Whether someone who is in good health would benefit from a severe calorie restrictive diet isn't clear. There are also risks with becoming too thin. Just look at anorexia nervosa.
Is there a maximum limit on how long humans can live?
It's an open question. All I can say is that there's been this remarkable increase in the last 200 years of survival to advanced ages. Demographic studies don't seem to indicate any slowing in this increase, at least in favored populations.
On the other hand, there are global deteriorations in the environment. The amount of airborne pollutants is increasing everywhere, and there are direct relations between the rate of vascular disease and the level of air pollutants. It's by no means certain that the lifespan increases of the last 200 years will continue at the same rate or be available to all people. My own hunch is that lifespan could increase considerably more, but it may depend on finances and access to top-level medical resources.