Book Review

Growing Old Gracefully

Human Longevity

N Engl J Med 1994; 331:485-486August 18, 1994

Article

Human Longevity
By David W.E. Smith. 175 pp. New York, Oxford University Press, 1993. $35. ISBN: 0-19-508313-X

This is not a book that promises extended longevity if the author's advice is followed. Examples in that category are the book by Roy L. Walford with a similar title (Maximum Life Span. New York: W.W. Norton, 1983) and a more recent one by Deepak Chopra entitled Ageless Body, Timeless Mind: The Quantum Alternative to Growing Old (New York: Harmony Books, 1993). Rather, it is a thoughtful, concise presentation of what we know about the biomedical and social determinants of human longevity.

The eight logically sequenced chapters of Human Longevity begin with a discussion of the difficulty of determining the limits of the human life span; Smith concludes that it is probably about 120 years. He goes on to discuss the changes in causes of death during this century and establishes for the reader that the current leaders are ischemic heart disease, cerebrovascular disease, and cancer. The topics of succeeding chapters include the biomedical, behavioral, and social determinants of longevity, the evolution of human longevity, and a look into the future. There is a final brief, reflective chapter, “Human Longevity Seen from the Perspective of This Book.”

Of particular interest to me are Smith's views on the relation between aging and disease. The credo within the community of gerontologists is that disease cannot derive directly from intrinsic aging processes, although a distinction between some phenomena of aging and disease is sometimes difficult. Smith introduces a different distinction. He thinks that aging consists of phenomena that have no certain relation to mortality, and senescence as capable of “causing disability and preceding mortality in ways that are often obvious.”

Smith notes that there is no common program for age-related functional decrements. Different systems decline at different rates, and in some aged persons some systems show no decline. Like almost all gerontologists, he leaves open the possibility of death due to a terminal breakdown in homeostasis, in the absence of fatal disease or trauma. He mentions Alzheimer's disease only in regard to its high prevalence in those over 85, although almost all elderly persons without dementia have the same brain lesions as those with dementia, and sometimes in equal numbers.

In the chapter on the evolution of human longevity, the principal focus is on so-called longevity-assurance genes, proposed some years ago by the late George Sacher. Smith lists a number of genes with intrinsic functions, including such familiar ones as DNA-repair genes, genes that specify free-radical scavengers, tumor-suppressor genes, and genes that ensure immune capacity. He considers that damage to these genes contributes to senescence, but their loss also has relevance to the genesis of disease. Moreover, Smith believes that “lifetime damage to DNA is an example of extrinsic aging,” but DNA damage can also result from intrinsically generated oxidative damage and other intrinsic phenomena.

In the final analysis, a resolution of the senescence-disease relation rests on reliably identifying causes of death. As Smith points out, this is no easy task. Death certificates are notably unreliable, and determining the cause of death by autopsy is hampered by the fact that the autopsy rate progressively declines from 55.3 percent among those 25 to 34 years of age to only 2.3 percent in those over 85. The prevalence of multiple diseases in the very old further confounds the determination of cause.

Smith poses an interesting question with respect to the relation of senescence and disease. If late-life diseases determine longevity, then is senescence simply an increasing predisposition to those diseases, and are the genes that control longevity simply genes for disease resistance? Resolution of the senescence-disease issue is not simply an academic exercise. Smith projects that by the year 2040 the over-85 population will have increased to 13 million from the present 2.5 million and the number of centenarians to 1 million from the present 30,000. Medical, ethical, and social issues will pose huge problems if the current prevalence rates for the three major diseases in the aged continue. But these problems may be even greater if the senescence-disease connection proves to be a direct one.

Herman T. Blumenthal, Ph.D., M.D.
St. Louis University School of Medicine, St. Louis, MO 63130