Biology of Aging

Roger B. McDonald

• Publisher: Garland Science
• Year: 2019
• ISBN:
  9780429638190
• Edition: 2
• Topic: Biowissenschaften
• Subtopic: Biologie

Biology of Aging, Second Edition presents the biological principles that have led to a new understanding of the causes of aging and describes how these basic principles help one to understand the human experience of biological aging, longevity, and age-related disease. Intended for undergraduate biology students, it describes how the rate of biological aging is measured; explores the mechanisms underlying cellular aging; discusses the genetic pathways that affect longevity in various organisms; outlines the normal age-related changes and the functional decline that occurs in physiological systems over the lifespan; and considers the implications of modulating the rate of aging and longevity. The book also includes end-of-chapter discussion questions to help students assess their knowledge of the material.

Roger McDonald received his Ph.D. from the University of Southern California and is Professor Emeritus in the Department of Nutrition at the University of California, Davis. Dr. McDonald's research focused on mechanisms of cellular aging and the interaction between nutrition and aging. His research addressed two key topics in the field: the relationship between dietary restriction and lifespan, and the effect of aging on circadian rhythms and hypothalamic regulation. You can contact Dr. McDonald at [email protected].

Related Titles

Ahmad, S. I., ed. Aging: Exploring a Complex Phenomenon (ISBN 978-1-1381-9697-1)

Moody, H. R. & J. Sasser. Gerontology: The Basics (ISBN 978-1-1387-7582-4)

Timiras, P. S. Physiological Basis of Aging and Geriatrics (ISBN 978-0-8493-7305-3)

1

Basic Concepts in the Biology of Aging

“Do not deprive me of my age. I have earned it.”

-May Sarton, poet and author (1912–1995)

IN THIS CHAPTER . . .

Biogerontology: Study of Biological Aging

Definitions of Biological Aging

How Biogerontologists Study Aging: Use of Laboratory Organisms in Human Aging Research

How Biogerontologists Study Aging: Comparative Biogerontology

How Biogerontologists Study Aging: Systems Biology

The Road Ahead

Why do we experience physical deterioration as we grow older? What are the reasons we live as long as we do? Most importantly, can we live healthier and longer lives? Humans have been asking these questions since gaining self-awareness, at least a million years ago. It has, however, only been since about 1930 that an organized scientific inquiry has focused on solving the mystery of biological aging, and only during the last 15–20 years that the underlying cause of aging has been understood. With the fundamental cause of aging described, we can now begin to answer the questions posed above. This text explores the research leading to our understanding of the cause of biological aging. We also discuss how discoveries regarding the cause of aging may lead to interventions that prolong a healthier life.

The description of the underlying cause of aging came as a surprise to many researchers because it has more to do with physics than biology. It turns out that biological aging occurs in accordance with the same physical laws that cause all matter in the universe to decay over time, the Laws of Thermodynamics. There are no genes or genetic pathways that have been evolutionarily selected to cause aging or regulate the rate of aging. Without genetic regulation, the types of dysfunction occurring with aging are random and highly individualized. In other words, “normal” aging does not exist.

We also know that many time-dependent functional losses and diseases, which were once associated with aging, are in fact related more to environmental factors than to the process of growing old. The understanding that our environment has a significant impact on health and aging reflects a major theme of this text. That is, you will learn that by controlling for or defending against the hazards of our environment, we can, for the first time in history, alter the rate of aging and prevent many diseases that appear later in life.

In this chapter, we focus on general principles and concepts used in the study of biogerontology, the scientific investigation of the biological mechanisms of how and why we age. We begin by tracing the brief history of biogerontology, from its origins to its rise as an independent subfield within the general discipline of biology. We then explore the underlying cause of aging and how biogerontologists define aging. We also examine how biogerontologists model human aging through the use of laboratory animals, the study of wild animals, and by quantitative analysis.

Biogerontology: Study of Biological Aging

Research in the biological sciences is all about searching for answers to the “how” and “why” of life. Biogerontology focuses on the “how” and “why” of aging. This relatively new field explores the biological processes that occur inside living things as they age and integrates research from many different fields, including biophysics, physical chemistry, molecular biology, neurobiology, biochemistry, genetics, evolutionary biology, medicine, and gerontology (the study of human aging and the problems of the aged). The scope of the field is broad—it can cover everything from molecular protein damage occurring inside the smallest cells to arterial atherosclerosis in a full-grown human adult.

Biologists began studying aging when human life spans increased

Although serious research in the life sciences can be traced back 400 years, the mechanisms of aging have been investigated rigorously for only the past 70–80 years. Why have the life sciences paid so little attention to the mechanisms of biological aging and longevity, the potential maximum age that an individual of a particular species can attain?

Until the beginning of the twentieth century, aging was an unimportant problem for biologists, because humans had relatively short life spans (the length of life of an individual organism). Between 1500 and 1900 CE, the average life span for people in Western Europe and the United States hovered between 35 and 45 years (Figure 1.1). For most of the population during this time, death commonly occurred at birth and, for women, in childbirth; childhood diseases killed millions of children under the age of 10; and infectious disease, such as influenza and tuberculosis, affected all age groups (Table 1.1). There were no compelling reasons to investigate a phenomenon—aging—that affected so few humans. Instead, biologists were focused on studying and curing the diseases that killed the majority of people before they had a chance to grow old. Thoughts about growing old were left to philosophers and theologians.

Figure 1.1 Average life expectancy at birth for humans in Western Europe and the United States from 1500 to 2010 ce. The numbers above the graph line are the percentage increases in life expectancy from one century to the next. The inset table shows life expectancy by decade for the United States since 1910. Note that the average life span did not rise above 50 years until after the 1900s. (Data from Gy Acsádi and J. Nemeskéri. 1970. History of human life span and mortality. Translated by K. Balas. Budapest: Akadémiai Kiadó. With permission from the University of Chicago Press; Arias E. 2010. U.S. life tables, 2006, Natl Vital Stat Rep 58:1–40. With permission from the National Center for Health Statistics; Goba.se. 2017. The World: Life Expectancy. http://www.geoba.se/population.php?pc=world&type=015&year=2017&st=rank&asde=&page=1.)

Table 1.1 Leading Causes of Death in United States for Years 1900 and 2015
1900	% of deaths	2015	% of deaths
Influenza and pneumonia	12	Heart disease	23
Tuberculosis	11	Cancer	22
Diarrheal disease	8	Chronic obstructive pulmonary disease	6
Heart disease	8	Unintentional injuries (medical errors)	5
Stroke	6	Stroke	5
Kidney disease	5	Alzheimer’s disease	4
Accidents	4	Diabetes mellitus	3
Cancer	4	Influenza and pneumonia	2
Senilitya	3	Kidney disease	1
Diphtheria	2	Suicide	1
aAll dementias were referred to as senility. Alzheimer’s disease had not yet been characterized.

Biogerontology became independent field of research during 1940s

Beginning around 1900, scientific and technological advances occurred that significantly increased life span. However, research on biological aging and longevity remained in the hands of only a few scientists. As a result, knowledge about the biological basis of aging and potential treatments for age-related dysfunction did not keep pace with the increase in life span. The slow pace of aging research between 1900 and the mid-1930s was due, at least in part, to the lack of national organizations that promoted aging research and provided a mechanism for scientists to exchange ideas and f...