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Biology LibreTexts

23.8: Adulthood

  • Page ID
    22632
  • Hmong Adults

    This colorful family portrait includes an elderly woman and her young-adult granddaughter from the Hmong ethnic group in Laos. Both grandmother and granddaughter are adults, but they are obviously far apart in age. What ages define the beginning and end of adulthood?

    Black H'mong family – Grandmother, mother, grandson- Sapa Vietnam
    Figure \(\PageIndex{1}\): Image used with permission (CC BY-NC 3.0; Hanay; via wikimedia.org; Black H'mong family Grandmother, mother, grandson Sapa Vietnam.JPG)

    Defining Adulthood

    Adulthood is the life stage between adolescence and death, but assigning exact ages to the beginning and end of adulthood is not easy. The event that marks the end of adulthood (death) is clear cut, but the age at which it occurs varies considerably. The beginning of adulthood is equally difficult to identify exactly. A person may be physically mature and a biological adult by age 16 or so, but not defined as an adult by law until older ages. For example, in the U.S., you cannot join the armed forces or vote until age 18, and you cannot take on many legal and financial responsibilities until age 21.

    Stages of Adulthood

    Shelby Harris 2011
    Figure \(\PageIndex{2}\): This 110-year-old man has been an adult for more than 90 years. (Rikeshia Davidson; public domain; via wikimedia.org; Shelby Harris 2011.jpg)

    Adulthood is generally the longest stage of life, potentially lasting for up to 80 years, or even longer. The man in Figure \(\PageIndex{2}\), for example, is pictured celebrating his 110\(^{\text{th}}\) birthday, so he has already experienced over nine decades of adulthood! Although most physical growth and maturation are finished by the time adulthood starts, many changes occur during these decades of life. As a result, adults of different ages may be quite different from one another. Therefore, it makes sense to divide the long period of adulthood into stages, such as the stages of early adulthood, middle adulthood, and old age.

    Early Adulthood

    Early adulthood coincides more-or-less with the 20s and early 30s. During early adulthood, people generally form intimate relationships, both in friendship and in love. Many people become engaged or marry during this time. Often, they are completing their education and becoming established in a career.

    Strength and physical performance typically reach their peak between 20 and 35 years of age (see photo below). Both males and females reach their peak fertility in the 20s, and for females, fertility starts declining in the 30s. Health problems in young adults tend to be relatively minor. Cancer is rare in this stage of adulthood, but there are a few exceptions, notably testicular cancer, cervical cancer, and Hodgkin’s lymphoma. The most common causes of death in young adulthood are homicides, car crashes, and suicides.

    Serena williams
    Figure \(\PageIndex{3}\): In 2010 at the age of 30, Serena Williams became the oldest female tennis player to be ranked number one in the world. Most professional tennis players peak in their 20s. (CC BY-NC 3.0; Wikigo; via wikimedia.org; Serena williams.jpg)

    Middle Adulthood

    Middle adulthood lasts from roughly the mid-30s to the mid-60s. Note that this age range is longer than the stage of life commonly called “middle age,” which is usually considered to range from about 45 to 65. During middle adulthood, many people raise a family and strive to attain career goals. Community involvement is also common in this life stage.

    Ellen Langer
    Figure \(\PageIndex{4}\): World-renowned psychologist Dr. Ellen Langer was 61 years old when this photo was taken. Nearing the end of middle adulthood, she was at the height of her career, and her most influential work — a book named Counterclockwise — was about to be published. The book deals with the subject of aging. (Robert Scoble from Half Moon Bay, USA [CC BY 2.0]) via wikimedia.org; Ellen Langer.jpg)

    Middle adulthood is the stage when most people start showing physical signs of aging, such as wrinkles and gray hair, like the gray-haired woman in the photo below. Typically, vision, strength, aerobic performance, maximal heart rate, and reaction time also start to decline during middle adulthood, although there is great individual variation in the ages at which these changes occur.

    Fertility continues to decline in females until menopause occurs, typically around age 52, after which a woman is no longer fertile. Male fertility starts to decline after age 40. Most middle adults start to diminish in height — especially females who have osteoporosis, which is common after menopause. Up to 1 cm of height per decade may be lost. Some people experience a small degree of cognitive loss during middle adulthood, but this usually goes unnoticed, because life experiences and accumulating wisdom generally compensate for the loss. Middle adulthood is also the time when many people develop chronic diseases such as type 2 diabetes, cardiovascular disease, or cancer. These diseases are the chief causes of death in middle adulthood.

    Old Age

    Old age begins in the mid-60s and lasts until the end of life. Most people over 65 years of age have retired from work, freeing up their time for hobbies, grandchildren, and other interests. On the other hand, retirement may lead to less social contact and loneliness. Many elderly adults may also be exposed to prejudicial treatment because of their age (ageism). For these and other reasons, depression is very common during old age, and people over the age of 65 have the highest rate of suicide.

    Physical and Cognitive Changes in Old Age

    Physical declines that started in middle age continue during old age. Declines generally occur in stamina, strength, reflex times, and the senses. As they grow older, most people become increasingly frail, with loss of muscle mass and lessened mobility. However, there are many exceptions. Some people remain fit and active in old age. The man in the photo below is an outstanding example.

    Fauja Singh in 2007
    Figure \(\PageIndex{5}\): Fauja Singh was 96 years old when this photo was taken in 2007. Singh took up marathon running when he was 89 years old and continued running competitively until the age of 102. As of 2016, he still held world records for the 90+ age group in several different running events. He has attributed his amazing abilities in old age to never smoking or drinking alcohol, eating a vegetarian diet, avoiding fried foods, going to bed early, and thinking positive thoughts. (Mithrandirthewise at en.wikipedia [Public domain] via wikimedia.org; Fauja Singh in 2007.jpg)

    Many people suffer from multiple chronic health conditions in old age. The immune system becomes less efficient, increasing the risk of serious illnesses, such as cancer and pneumonia. As people age, the number of brain cells also decreases. Nearly half of those over the age of 85 years exhibit at least mild cognitive impairment. Diseases such as Alzheimer’s disease that cause serious and permanent losses of mental function also become more common.

    Age at Death

    Old age ends at death, but when is death likely to occur? The average age at death is reflected in the statistical measure known as life expectancy. Life expectancy is defined as the average time an individual is expected to live. It is based on the year of their birth and their current age and gender. In the United States in 2015, life expectancy at birth was 77 years for males and 82 years for females.

    Life expectancy is just an average, and many people outlive the life expectancy value for their year of birth and gender. In fact, by the year 2050, a projected half a million Americans will be at least 100 years old, thanks to a large number of baby boomers and advances in health care. Is there an upper limit on old age? In 2016, scientists identified the maximum human lifespan as 115 years on average, with an absolute upper limit of 125 years. These numbers may increase if scientists learn how to slow down aging. This requires understanding the causes of aging.

    Causes of Aging

    Why do we decline in so many ways as we age? Why is there an upper limit on the human lifespan? The causes of aging (and ultimately death) are not known for certain, but a number of factors have been proposed. These factors fall into two general categories: programmed factors and damage-related factors.

    Programmed Factors

    Telomere caps
    Figure \(\PageIndex{6}\): The white spots at the ends of these gray human chromosomes are telomeres. Cells lose the ability to divide when their telomeres become too short through repeated previous cell divisions. (CC BY-NC 3.0; U.S. Department of Energy Human Genome Program)

    Programmed factors follow a biological timetable and may be a continuation of the timetable that regulates childhood growth and development. An example of a programmed factor is the shortening of telomeres. Telomeres are regions of repetitive nucleotide sequences at the ends of chromosomes (Figure \(\PageIndex{6}\)). They may normally serve a variety of functions, such as protecting chromosomes from fusion with neighboring chromosomes. Telomeres become shorter each time a cell divides, and when telomeres become too short, the cell stops dividing and dies.

    Damage-related factors include internal and external assaults on the organism that produce cumulative damage to DNA or cells. Many damage-related factors have been proposed, including the following:

    • Exposure to environmental mutagens: Mutagens may damage DNA, and DNA damage can prevent cells from dividing. There are several checkpoints in the cell cycle where cell division is halted if DNA damage is detected.
    • Accumulation of waste products in cells: Waste products may interfere with normal cellular metabolism. The amount of waste might reach a level at which cells can no longer function.
    • excessive amounts of highly reactive chemicals called free radicals (for example, OH-): Free radicals can damage DNA and cells, and contribute to diseases such as cancer and cardiovascular disease. These diseases are major causes of death in the later decades of life. Some causes of excess free radicals include exposure to environmental pollutants, drinking alcohol, eating trans fats, and smoking tobacco.

    Feature: Reliable Sources

    Male borderline underweight
    Figure \(\PageIndex{7}\): This man’s weight is at the lower end of the normal range for his height. Maintaining a low body weight might help him live longer by slowing the aging process — or at least it might if the calorie-restriction theory of anti-aging is correct. In this context, calorie restriction refers to eating a low-calorie diet while still maintaining proper nutrient intake. Calorie restriction, in turn, leads to low body weight. (Fredrik; public domain. via wikimedia.org; Male borderline underweight.jpg).

    Popular media outlets sell books, diets, and programs that promote the calorie-restriction theory of anti-aging. They make money by telling people how and why to eat less in order to live longer. Is this just hype or wishful thinking? Or are there real longevity benefits to calorie restriction? Research reliable sources to find answers to these questions.

    Summary

    • Adulthood is the stage of life between adolescence and death. The age at which death occurs varies considerably. The age at which adulthood starts varies depending on whether adulthood is defined as biologically or legally. Adulthood is usually the longest stage of life, potentially lasting for many decades. It is generally divided into stages, such as the stages of early adulthood, middle adulthood, and old age.
    • Early adulthood coincides more-or-less with the 20s and early 30s. During this stage, many people complete their education, start a career, and form intimate relationships. They may marry and start a family. Strength and physical performance typically reach their peak during early adulthood, as does fertility in females.
    • Middle adulthood lasts from about the mid-30s to the mid-60s. Many adults raise a family and attain career goals during this stage. This is also the stage when most people start showing physical signs of aging and experience physical declines, including a decline in fertility. Some cognitive loss may also occur, and many people develop chronic diseases such as type 2 diabetes during middle adulthood.
    • Old age begins in the mid-60s and lasts until death. Most people over the age of 65 have retired and have more free time. Some may have less social contact and experience loneliness, and many experience ageism. Physical declines that started in middle adulthood continue during old age. Most people become increasingly frail and have a greater risk of serious illnesses such as cancer. Cognitive impairment is common in old age and may become very serious in cases of disorders such as Alzheimer’s disease.
    • The average age at death is given by the statistical measure called life expectancy, which varies by birth year and gender. For people born in the United States in 2015, life expectancy was 77 years for males and 82 years for females. Increasing numbers of Americans are living to be older than 100. The average maximum human lifespan is estimated to be 115 years, with an absolute upper limit of 125 years.
    • The causes of aging (and ultimately death) are not known for certain. Factors that have been proposed fall into two general categories: programmed factors and damage-related factors. An example of the former is the shortening of telomeres, and an example of the latter is mutations in DNA due to exposure to environmental mutagens.

    Review

    1. Define adulthood.

    2. Why is it difficult to give exact ages for the beginning and end of adulthood?

    3. List the stages of adulthood.

    4. Describe the stage of early adulthood.

    5. What is the age range of people in middle adulthood, and what are some of the changes that typically occur during this life stage?

    6. Define old age, and describe this stage of life.

    7. What does life expectancy measure? Identify two factors that influence life expectancy. What was the life expectancy of Americans born in 2015?

    8. What is the maximum human lifespan?

    9. Discuss possible causes of aging.

     

    10. A 40-year-old person is typically considered to be ________________.

    A. in old age

    B. middle-aged

    C. in middle adulthood

    D. B and C

    11. Compare the chief causes of death between early adulthood and middle adulthood.

    12. Why do you think scientists are studying how to lengthen telomeres?

    13. Free radicals and mutagens both cause damage to ________ .

    14. True or False: Once a person reaches adulthood, their height stays constant.

    15. True or False: Life expectancy is generally lower in females than in males.

    Explore More

    In some regions of the world called "blue zones" people live to very old ages. Watch this video to learn about the characteristics of their lifestyles that they have in common:

    Dr. David Sinclair is a researcher who studies the causes of aging, and how we may be able to inhibit the process. Watch the talk below to learn more about this exciting research.