Human Longevity: How Old Can We Grow?

By James R. Carey

With the first members of the baby boom generation due to celebrate their 65th birthdays in 2011, some of the most contentious debates in demography today are centered on questions concerning the human life span. Because of the sheer number of baby boomers in the United States, the economic ramifications for accurately predicting survival rates are enormous; even small differences between actual rates and the government’s predictions will determine whether Medicare and Social Security programs are solvent or insolvent. Future changes in longevity will affect all social institutions and fundamental beliefs throughout the world—it is not possible to change one segment of any society without affecting the entire network of relations both within and between societies.

The increase in life expectancy at birth in the United States from less than 48 years in 1900 to nearly 77 years in 2000 is considered by most demographers as one of the greatest achievements of the 20th century. Recent evidence from Swedish death records showing that human life span (the record age reached by some individuals) has been increasing for at least the past 130 years suggests that we are not yet approaching our longevity potential.

One of the most compelling arguments that human longevity will continue to increase is based on an extrapolation model published recently in Science by my colleague James Vaupel, founding director of the Max Planck Institute for Demography in Germany. Vaupel identified the country with the highest life expectancy for each of the past 160 years (referred to as “best-practice data”) and showed that life expectancy increased linearly by 2.5 years per decade (three months per year) beginning in 1840, with a life expectancy of 45 years in Sweden, through 2000, with a life expectancy of 85 years in Japan. This “best practice” model thus forecasts a life expectancy of 100 years in at least one developed country in the world by the end of the century; in other words, a centenarian life span in the future could well become the norm rather than the exception.

One of the challenges in forecasting mortality patterns is that virtually nothing is known about why some individuals live to middle age and others live to extreme ages. Indeed, the life-style recommendations that follow from biomedical and social studies are unremarkable: Do not smoke, use alcohol in moderation, stay socially connected, exercise, avoid fatty diets, shed excess weight and minimize risk of accidents. Simply put, there is not a single “secret” to long life, and there is certainly no crystal ball for predicting scientific breakthroughs that can delay aging and prolong life.

However, there are several basic health and biomedical concepts that are likely to have an important bearing on future improvements in life expectancy. These include

• healthful living, which consists of avoiding disease and disability, maintaining mental and physical function, and continuing engagement with life;

• disease prevention and cure, as cutting-edge and emerging medical technologies such as molecular medicine, gene therapy and pharmacogenomics are brought to bear on debilitating diseases like arthritis, cancer, cardiovascular diseases and stroke;

• organ replacement and repair, as tissue-engineering technologies are used to produce bioengineered bone, blood vessels, liver, muscle and nerve conduits that are used to repair or replace tissues and organs in aging bodies; and

• aging arrest and rejuvenation, with the development of therapies to modify the aging process. Reducing the rate of actuarial aging would increase life span far more than would improvements from any other single mechanism.

Increases in longevity are already having and will continue to have several important impacts on society.

Some individuals will live to new extreme or record ages. Although the record-holders themselves have virtually no direct effect on society, they are important harbingers of the future and a positive reflection of the extreme manifestations of improved health. Just as the first appearance of nonagenarians (90s) and centenarians (100s) was probably in the 19th century and of supercentenarians (110s) in the 20th century, someone this century will probably break the current record of the Frenchwoman who died in 1997 at the age of 122 years and 164 days.

People will remain functional and healthy at older ages. The 60- and 70-year-olds of today have the same mortality risk as the 45- and 61-year-olds in 1900. In other words, the frail elderly of yesterday are the more robust seniors of today and tomorrow. It is this new and expanded group of healthy elderly who will shape future societies through their voting, entitlements and spending.

And finally, life cycles will change. As life span and life expectancy increase, people plan their lives differently and thus change the timing, sequencing, duration and spacing of key events, including marriage and childbearing, education, working life and retirement.

In long-lived societies the average age of childbearing will probably increase. At the same time, though, childbearing will be compressed into a narrower band of the life cycle, increasingly between the ages of 30 and 40 years, as women delay having children but face reduced fertility as they age. However, that upper childbearing age might increase if the reproductive technologies that enable women to conceive, gestate and give birth to children at older ages become less expensive, widely available and adopted by large numbers of women.

In the future society of long-lived people, a new rhythm of social maturity will impinge upon other aspects of family life in subtle ways. For example, the increase in the age of parenthood will affect the degree of parental authoritarianism, and the prevalence of one-child families will affect the patterns of health assistance, of flows of money in both directions and of child care.

The expansion of early adulthood will also likely continue. Whereas the chronological threshold to adulthood was age 21 in the baby boom generation, that threshold is now believed to be moving toward age 30. This expansion of early adulthood has a number of societal implications, including a possible mismatch of institutions and individual timing. For example, more young adults may have no health insurance because they are too old to be covered by their parents’ plans but are not yet economically secure enough to have their own. On the other hand, young adults will have more time for career and partner searches—social and sexual interactions with potential spouses may last a decade or more, and career experiments of entry, exit and re-entry are possible due to less time pressure to support a family and achieve economic independence.

The sequence of life events may also change. The traditional sequence in the first half of the 20th century was get an education, leave the nest, enter the labor force, marry and begin a family. With the extended transition into adulthood, childbearing might precede marriage, entry into the work force might precede departing the nest, and divorce might be followed by a return to the nest.

As our society ages, new generational constellations will begin to emerge, including four- and even five-generation families with new contexts for sorting out needs and resources of the family. With most families consisting of two parents and a single child, extended families will no longer have aunts, uncles and cousins. Instead, these groups of kin will be partly replaced by the enduring presence of long-lived older family members—great-grandparents through great-grandchildren.

The age at which full retirement benefits start is likely to continue to rise, to the early to mid-70s in the near term and to the late 70s, early 80s and beyond as life expectancy continues to increase. To maintain the stock of human capital available to the U.S. economy, strategies will have to be adopted that keep workers in the labor force for longer periods of time. Highly skilled and educated older people, instead of being retired, may be offered continuing professional relationships that preserve their skill and knowledge for the employer while giving the workers flexibility. A model already in use comes from academia: the professor emeritus.

Education in the long-lived society will become a seamless web in which primary and secondary education, undergraduate and graduate training, professional schooling and apprenticeships, internships and on-the-job training, and continuing education and lifelong learning are a continuum. The pace of science and society will be so rapid that those who do not adopt a lifelong strategy of continuing education will be left behind. Universities will need to adapt to these changes by expanding distance-learning capabilities to better accommodate the educational demands of older people in the workplace who cannot attend classes on campus.

We have just begun the “century of biology,” and eventually some of the most profound secrets of life will be discovered, including those that further extend human life span. The deep currents of change arising from aging societies and increasing numbers of long-lived people will continue to affect our state, our country and our world in unexpected and even startling ways. By simply living our lives, we are an inextricable part of a historical demographic stream that is transforming our world from one consisting of mostly youth to one consisting of an unprecedented number of older people, some of whom will live to ages never before realized and all of whom will shape societies in ways never before imagined.