29 Aging Starts Right After Growing Ends

Sabine Zempleni and Sydney Christensen

The world's oldest runner, Fauja Singh, on life since his retirement | Running | The Guardian

Image copyright 2013 TheGuardian.com Included under the provisions of fair use under U.S. copyright law.

Fauja Singh is 102 and is believed to be the world’s oldest runner. Since taking up running, aged 89, he has run nine full marathons. Singh retired from competitive races in February after completing a 10K race in Hong Kong. But he still jogs every day in east London.” The Guardian 2013

Marathon running at the age of 102? Watch Mr. Singh run his last competitive race: https://www.bbc.com/news/av/uk-21565970 .

What allows a person to live a long and healthy life with this level of activity? Why are some seniors able to start running marathons in their 80s, while others are not able to walk up a flight of stairs? Many scientists are interested in the biological mysteries of aging. The ultimate goal of geriatric research is to understand why some people live such a long and active life, then use this knowledge to help others achieve a long quality life as well.

During this chapter we will define adulthood and old age, and look at a very broad definition of aging.


Before we jump in, make sure to review (or learn) previous course material about life-expectancy:


The oldest reported age at death that was ever recorded was 122 years and 164 days, the age at death of Jeanne Calment, a French supercentenarian. This brings up the question: Is there is a natural limit to life? Although the answer is heavily debated by scientists who either align with the “limited” or “limitless” perspective, it is agreed upon that life-expectancy has undergone enormous changes over the last 100 years:

  1. Since the end of the 19th century life expectancy has immensely increased.
  2. The number of octogenarians, nonagenarians and centenarians (80-100 year olds) is steadily increasing.

We will start with a couple of definitions.

Life expectancy is the average amount of time a person is expected to live given their birth year or period. The most common life expectancy used is the life expectancy at birth, which expresses the average years a newborn infant can expect to live. Keep in mind that this average includes infants who die in the first year of life, young individuals having a car accident, and so on.

In addition to the life expectancy at birth, we can also look at the life expectancy for 65 or 75 year old adults. This will allow us to understand how long a 65 year old person can expect to live after surviving childhood diseases, accident prone teen and young adult years, and middle age with early heart attacks.

Over the last 150 years, the life expectancy at birth in the US rose from an average of 40 years to an average of almost 80 years today. If you look at the life expectancy graph above, you also see that since the 1950s, life expectancy has steadily risen without much fluctuation.

By the way, the deep dip in 1918 reflects the impact of the Spanish flu pandemic; we might see a dip stemming from the COVID-19 pandemic as well.


The COVID-19 pandemic dip: The statistics are in. As expected we saw a dip in life expectancy in 2020 related to the huge number of COVID-19 deaths worldwide. This was expected based on the 1918 flu pandemic data, which featured a similar dip. During a pandemic many people die, and this impacts the life expectancy of the infants born during those years. At this point, US researchers are ringing the alarm bells though. While other comparable countries recovered from the dip in life expectancy, the US life expectancy keeps steeply declining for a second year in a row. Here is the article: https://www.npr.org/sections/health-shots/2023/03/25/1164819944/live-free-and-die-the-sad-state-of-u-s-life-expectancy


The question is now: what contributes to the steady and smooth rise in life expectancy?

Amazing medical innovations during the 20th century are the major contributors. Development of vaccines and antibiotics reduced the mortality of children and adults alike. Before the discovery of vaccines and antibiotics, infectious diseases were the top cause of death. A simple cold, the flu, or any other infectious disease could cause death at any time during life. Many children died due to diseases most parents are not familiar with today: polio, measles, mumps, rubella, diphtheria, tetanus and pertussis. Before some parents started refusing childhood vaccinations, these dangerous diseases were almost eradicated.

New medical procedures and drug development expand life today, even if a person develops a non-communicable diseases.

Improved hygiene (personal, medical, and food safety) prevents the spread of communicable diseases. The chlorination of water stopped epidemics of gastrointestinal diseases in industrialized countries almost completely.

The other big factor is improved nutrition. Our food system not only became safer, but food became cheaper and more widely available. Social programs such as SNAP (formerly food stamps) ensure that people living in poverty will not starve to death.


If you ever have some time, I recommend reading The Jungle (1906) by Upton Sinclair, an American journalist and novelist. He went undercover in the Chicago stockyards to describe the harsh conditions and exploited lives of immigrants in Chicago. You will also learn a lot about the food production system back then. I only made it 3/4 through the book because the conditions described were so horrible that I could not take it any longer!


When looking at the life expectancy for 65 and 75 year olds we see that it has continued to increase during the last decades. This is absolutely amazing! Unfortunately, this is not the case for everyone:

Equity: There are disparities in life expectancy associated with both race and sex. The life expectancy at birth is 6 years higher for white Americans than Black Americans. We have previously discussed this diversity issue; recall that Black Americans suffer more from T2D and other chronic diseases, as well as maternal mortality. Women live longer than men.

Comparison to other countries: The life expectancy in the US might be high, but it is not exceptional. Other industrialized countries make more progress (see graph above).

Healthy life expectancy: Long life is not enjoyable if the quality of life is low, thus the healthy life expectancy takes the years of ill health into account. It is the average amount of years in good health a person can expect at birth. The average in the US is approximately 66 years, and hasn’t increased in the last two decades. This gap of 13 years is the reason why many seniors live their last years with a low quality of life.



You Will Learn:

1. Aging is the gradual, progressive loss of physiological function over a lifetime.

  • The Definition of Old Has Changed Throughout History
  • Biologically, an adult is defined by having reached physical maturity. Physical maturity includes that growth is mostly completed and sexual maturity is reached.
  • There are several categories of adults: Young adulthood, middle adulthood, older adulthood.
  • There Are Several Categories of Old: Young-old, middle-old and old-old

2. The onset and acceleration of the aging process varies widely.

3. Effective age can be estimated taking chronic disease symptoms into account.



Aging is the Gradual, Progressive Loss of Physiological Function Over a Lifetime 


Becoming an adult has several dimensions: biological, psychological, and social. From the standpoint of nutrition sciences, we are mostly interested in the biological dimension.

Biologically, an adult is defined as having reached physical maturity: the point at which growth is mostly completed and sexual maturity is reached.

This simple definition would include everybody from 19 to 120 years old, and we can all agree that a 19 year old is very different from a 120 year old. Once we reach adulthood, our bodies do not remain in the same physiological state for the rest of our life. While we will not grow and physiologically mature anymore, there are still many physiological changes occurring.


This is why we subdivide adulthood into three general age groups:

  • Young adulthood:  19 – 30 years old
  • Middle adulthood: 31 – 50 years old
  • Older adulthood:   51 – 70 years old

Keep in mind that this is a very rough definition. You will later learn that for many people the chronological age does not necessarily match the physiological age.

Young adulthood: the time when our body is physiologically at its peak: peak bone density is reached, lean body mass is highest, metabolic processes tend to run flawlessly. Aging processes are present, but not noticeable.


Emerging Adulthood: Notice that the biological definition does not fully describe this age group. When we look at young adults from a socio-psychological standpoint, it is clear that being an adult is not as easy as reaching the age threshold of 19 years. Many 19 year olds start college and certainly do not feel like an “adult.” This phase in life can be described as emerging adulthood: a time of identity exploration marked by instability and self-focus. Although most young adults feel in-between childhood and adulthood, the timing when young people transition into adulthood and feel like an “adult” can greatly vary.


Middle adulthood: After age 30, the aging process is ongoing, but is only barely noticeable in healthy adults living a healthy, active lifestyle . 

Older adulthood: Age 50 is usually the time when aging starts to become more noticeable. People notice their age, even if they are healthy and fit. Joints become stiffer and achy, weight becomes much harder to maintain. If the person has had an unhealthy lifestyle, symptoms of chronic diseases start showing.


The image depicting the leading causes of death (middle of the infographic above) illustrates that aging tends to speed up in later life.

The main causes of death for young adults are injuries, followed by homicides and suicides. Chronic diseases play only a minor role. As we age, the causes of death are more influenced by the aging process and lifestyle—shifting towards cancer and heart disease—especially in older adults.

You might have noticed that the adulthood definition only reaches until the age of 70. Is everybody above just old and not an adult anymore?



Next Question: What Is Old?

Old people are often separated from older adults because they start having different needs. Of course they are still adults! For teens and young adults, being old seems to start at middle age, sometimes even earlier. This is then countered by remarks such as 50 is the new 30 ~ I agree 🙂 For the sake of this course, we will use the scientific definition though.


Brief Excursion: Ageism Is Prevalent In Our Society

Worldwide we see a shift towards youth-centered societies. Speed, adaptability, mobility, and technology savviness are valued along with youthful beauty. Seniors are increasingly seen as slow, incompetent, taking up more resources than they provide value to society, and as having too much power. This trend gives rise to intergenerational tensions and increasing ageism.

When you study the section about aging, you will learn that we distinguish between unavoidable, physiological aging processes and factors accelerating the aging process. This distinction is necessary to study nutrition sciences and ultimately develop interventions. But, this approach has an inherited danger for ageism. By showing centenarians—we amplify what is possible in an encouraging, positive way—but we need to be careful that this positive approach does not lead to individual blame.

Complex ageism also sneaks into our interactions with seniors in daily life and health care settings.

When we think about ageism, we initially tend to think about hostile ageism. Hostile ageism is a negative view of seniors as incompetent, too slow to keep up with technological developments, too set in their ways to be adaptable and mobile in a work setting, too weak to participate fully in life. In short, hostile ageism assumes that seniors are not able to contribute to society, but use up lots of resources.

The other facet of ageism we tend to be less aware of is called benevolent ageism. At first glance, this approach to interacting with the elderly seems positive. Seniors are approached warmly, but are seen as incompetent and vulnerable or in need of help to function. Decisions are made in the best interest of the seniors, and they are treated similarly to children. People engaging in benevolent ageism mean well, but reduce the autonomy and self-efficacy of the elderly person. If you talk with seniors, it is common to hear that benevolent ageism is pervasive and extremely aggravating.

In conclusion, we all need to evaluate how we interact with seniors. It is important not to stereotype by numerical age. Seniors of the same age can range from very vulnerable to fully autonomous. It is the job of a healthcare professional to evaluate each health care situation individually, and involve the patient in the decision making process as much as possible.



The Definition of Old Has Changed Throughout History

I read an interesting article about defining the beginning of old age throughout history when I prepared for this class (I have posted a link at the bottom of the page if you are interested.) Age has always been used to organize members of a society, and discussions have always been sparked by questions such as who is an adult, when is the peak of life, and what is old age?



For a long time, “being old” was defined by how well somebody functioned in daily life, and from that idea benchmarks were deducted.

Women were considered to age about 10-20 years earlier than men. This stemmed mostly from the inability to bear children after menopause or—as young and fertile was considered the beauty standard back then—the loss of sexual attractiveness. Based on these factors, women were at times considered old after reaching an age of 40–45 years. Men were considered at their peak during those years. Interestingly, the scientific facts are quite the opposite. If women survived childbirth, they outlived men in all societies during all times.

Other times, the “old” benchmark was set about 5–10 years before the predictable death. For example, during colonial times the age of death was between 40 and 65 years. Later, the definition varied with the ability to work, and this varies with occupation. If a job is physically demanding, old age is reached earlier.

The definition of old age is also determined by cultural norms, and may rely on questions such as can the person still contribute fully to society? What are the tasks the society expects? Is the person able to perform job related tasks and tasks of daily life? Is the person still independent? These ideas refer most closely to biological age and onset of frailty. Cut-offs for being old vary by cultures. While the US tends to have a cut-off at 65 years, in many developing countries this age cut-off for old is set earlier, sometimes as soon as 50 years.

Where does this 65 year cut-off in the US stem from? When the pension system in Western countries was developed, old age was equated with receiving a pension or going into a deserved retirement. The age cut-off was set to 65 years which became the new definition. Today, people live longer and the age of retirement shifts along to ensure that social security funds are sufficient. During the last decades we realized more and more that retirement age does not necessarily describe the starting date for old age.



We Narrowed It In: There Are Several Categories of Old

Setting the “start of old age” to 65 in the US somewhat narrowed the life stage of “old.” However, a group of all 65+ year old adults is not a homogenous group. Therefore science developed additional categories.

The idea of having several categories of old is not new. According to Hippocrates there is a springtime of old age which lasts to 70 years, a green old age from 70 to 75, a real old age from 75 to 80 and ultimate old age from 80 to 90. People reached 100, but it was a rare event.


Today there are several scientific definitions; a rough estimate places the young-old from 65 to mid 70s, middle-old from 75 to 85 and then the 85+ as old-old. This chronological definition helps when study participants need to be categorized to allow comparability across different studies, but for health care purposes, this definition does not work well. We all know 80 year old people who are more fit than 70 year old people.

Today, we determine if somebody is a old by chronological age. But if somebody ages prematurely or stays youthful for a long time, then chronological age does not line up with the effective age. In order to understand this discrepancy, and adjust (as a health professional) how we communicate and work with seniors, we need to understand the aging process.



The Onset and Acceleration of the Aging Process Varies Widely


First, here is the bad news: all physiological functions lose efficiency throughout life. And yes, that process starts right away once growth and physiological maturation is completed.

During growth, tissue is built and modified; however, once growth and maturation is completed, the focus shifts to maintenance of tissue. After many cell divisions due to tissue growth and maintenance, cells start aging. This in turn triggers loss of some organ and tissue function, as well as adaptability to our environment.

The good news is that initially this is a slow process. Once older adulthood is reached, the wear and tear starts to speed up slowly, and reaches the fastest acceleration in the senior years.

Some loss of efficiency and adaptability is clearly visible: the need for reading glasses, having trouble seeing at night while driving, getting less flexible, and some loss of strength. Does that describe your parents and grandparents?

Other changes are less visible:

  • Our immune system will age, and immune cells will not fight off pathogens as easily. Many older people—not all though—are sick more often and tend to experience communicable diseases such as the flu or cold more severely.
  • After eating, returning to homeostasis takes longer which increases the risk for developing, for example, T2D.
  • Other systems become less able to endure the environment we are living in. Ask any aging adult and they will tell you that while they can deal with stress, high temperatures, or strenuous exercising, it becomes increasingly harder to bounce back afterwards.
  • Declining function and decreasing capacity to endure stressors increase the risk for disease and injury with age.


What is returning to homeostasis after a meal?

When we start a meal, the smell and taste of food triggers neurological and hormonal signals to get our body ready for digestion. Once eating starts, an array of digestive and metabolic processes are started:

  • Mouth: Taste receptors and the somatosensory system signal incoming food type. Digestive enzyme production increases depending on the detected macronutrients. Gastric juice production and GI motility also increase.
  • Stomach: Stretch receptors regulate intake of food amount and short-term satiety
  • Small intestine: Receptors provide information about nutrient composition of food and activate appropriate metabolic pathways. Stretch receptors provide information about amount.
  • Metabolism: Presence of nutrients in the blood circulation and cells modulate metabolic pathways.

Once all nutrients are metabolized or stored, this machinery goes back to normal, which is called returning to homeostasis. Slower return to homeostasis makes us more vulnerable for chronic diseases. For example, blood glucose levels stay elevated longer, increasing the risk for T2D.



Effective Age Can Be Estimated Taking Chronic Disease Symptoms Into Account

The primary focus on promoting healthy behaviors is to increase the likelihood of a long life, with minimal chronic disease and cognitive decline. It would be great if we knew how well we would age, and could receive some sort of treatment if aging progresses too fast!

While science is not anywhere close to providing treatment for aging, scientists have developed the concept of the “effective age” based on what we know today about the aging process.



Even in healthy individuals, the risk for age-related chronic diseases such as cancer, T2D, CVD, Alzheimer’s, dementia, or reduced cognition increases due to cellular aging processes. More details about cellular aging later.

Individual differences come in part from genetic predisposition, but lifestyle choice is another much larger factor. Developing chronic diseases early due to an unhealthy lifestyle speeds up aging, reduces quality of life, and hastens death.

This is how the concept of the effective or biological age was developed. Effective age tries to calculate the true age based on risk factors for chronic diseases. Mathematical calculations collect the risk factors, calculate a risk level, and plot the risk level against the chronological age.

Based on scientific data, the red curve depicts the relationship between risk level and chronological age in healthy adults. Using this curve, this risk level is extrapolated (see infographic above, upper right side) to the biological/effective age. If the risk level is low, the effective age is lower than the chronological age. If the risk level is high, the effective age is higher than the chronological age.

This concept could be used to design personalized health care, but at this point in time the science is not precise enough. Currently, the primary purpose of the effective or biological age is to generate awareness.


Calculate Your Heart Age

Here is an example to calculate effective heart age: NYC Health: Calculate Your Heart Age.

Other calculators are designed to calculate lung and brain age. Effective age calculators were developed to show people diagnosed with an age-related disease how the disease can impact the aging process and the risk of dying. Studies showed that many patients are motivated by this.


Effective age is a very crude estimate of aging though, and assumes that developing a chronic disease has the largest impact on aging. This brings up the question of how scientists research the complex concept of aging. In order to gain a better understanding of the aging process, aging is broken up into several components:

  • Physical capabilities: Describes the appearance of an adult. How much strength does the person have? Does the person function in daily life without undue effort? Only partially? Is the person still able to exercise intensely?
  • Physiological functioning: Determined by running lab tests on blood and urine, physiological functioning describes the biophysical and biochemical processes, homeostatic control mechanisms, and communication between cells.
  • Endocrine function: Part of physiological functioning, and describes changes in hormone secretion and interaction (for example: HPG axis, HPA axis, insulin secretion).
  • Immune Functioning: Ability of the immune system to work in a balanced way, including chronic systemic inflammation as well as the ability to identify and remove threats efficiently.
  • Cognitive functioning: Includes everything from mild cognitive decline (forgetting things, less ability to focus, learn or memorize) to the development of dementia and Alzheimer’s disease.

Some of the aging processes I just described are unavoidable. They are determined by wear and tear as well as genetic predisposition. During the next chapters, you will learn about the physiological and molecular aging processes, including how chronic diseases accelerate aging processes.


Editor: Sydney Christensen, Meryn Potts

NUTR251 Contributors:

  • Spring 2020: Ericka Knapp, Brittany Southall, Miranda Haverdink, Kennedie Engles, Krissy Krager, Kendyl Heuertz
  • Fall 2020: Bryson Krull, Kaitlyn Higgins, Morgan McCain, Collin Mahler



Avendano M, Kawachi I. Why do Americans have shorter life expectancy and worse health than do people in other high-income countries?. Annu Rev Public Health. 2014;35:307-325. doi:10.1146/annurev-publhealth-032013-182411

Covey HC. The definitions of the beginning of old age in history. Int J Aging Hum Dev. 1992;34(4):325-337. doi:10.2190/GBXB-BE1F-1BU1-7FKK, https://pubmed-ncbi-nlm-nih-gov.libproxy.unl.edu/1607219/ (you need to go through the UNL library system to PubMed to have access)



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Nutrition Through the Life Cycle Copyright © 2020 by Sabine Zempleni and Sydney Christensen is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License, except where otherwise noted.

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