The body changes with aging because changes occur in individual cells and in whole organs. These changes result in changes in function and in appearance.
As cells age, they function less well. Eventually, old cells must die, as a normal part of the body's functioning.
Old cells sometimes die because they are programmed to do so. The genes of cells program a process that, when triggered, results in death of the cell. This programmed death, called apoptosis, is a kind of cell suicide. The aging of a cell is one trigger. Old cells must die to make room for new cells. Other triggers include an excess number of cells and possibly damage to a cell.
Old cells also die because they can divide only a limited number of times. This limit is programmed by genes. When a cell can no longer divide, it grows larger, exists for a while, then dies. The mechanism that limits cell division involves a structure called a telomere. Telomeres are used to move the cell's genetic material in preparation for cell division. Every time a cell divides, the telomeres shorten a bit. Eventually, the telomeres become so short that the cell can no longer divide.
Sometimes damage to a cell directly causes its death. Cells may be damaged by harmful substances, such as radiation, sunlight, and chemotherapy drugs. Cells may also be damaged by certain by-products of their own normal activities. These by-products, called free radicals, are given off when cells produce energy.
How well organs function depends on how well the cells within them function. Older cells function less well. Also, in some organs, cells die and are not replaced, so the number of cells decreases. The number of cells in the testes, ovaries, liver, and kidneys decreases markedly as the body ages. When the number of cells becomes too low, an organ cannot function normally. Thus, most organs function less well as people age. However, not all organs lose a large number of cells. The brain is one example. Healthy older people do not lose many brain cells. Substantial losses occur mainly in people who have had strokes or who have Alzheimer's disease or Parkinson's disease.
A decline in one organ's function, whether due to a disorder or to aging itself, can affect the function of another. For example, if atherosclerosis narrows blood vessels to the kidneys, the kidneys function less well because blood flow to them is decreased.
Often, the first signs of aging involve the musculoskeletal system. The eyes, followed by the ears, begin to change early in mid-life. Most internal functions also decline with aging. Most bodily functions peak shortly before age 30 and then begin a gradual but continuous decline. However, even with this decline, most functions remain adequate because most organs start with considerably more functional capacity than the body needs (functional reserve). For example, if half the liver is destroyed, the remaining tissue is more than enough to maintain normal function. Thus, disorders, rather than normal aging, usually account for most of the loss of function in old age.
Even though most functions remain adequate, the decline in function means that older people are less able to handle various stresses, including strenuous physical activity, extreme temperature changes in the environment, and disorders. This decline also means that older people are more likely to experience side effects from drugs.
Bones and Joints
Bones tend to become less dense. Thus, bones become weaker and more likely to break. In women, loss of bone density speeds up after menopause because less estrogen is produced. Estrogen helps prevent too much bone from being broken down during the body's normal process of forming, breaking down, and re-forming bone.
Bones become less dense partly because they contain less calcium (which gives bones strength). The amount of calcium decreases because the body absorbs less calcium from foods. Also, levels of vitamin D, which helps the body use calcium, decrease slightly. Certain bones are weakened more than others. Those most affected include the end of the thighbone (femur) at the hip, the ends of the arm bones (radius and ulna) at the wrist, and the bones of the spine (vertebrae).
Changes in vertebrae at the top of the spine cause the head to tip forward, compressing the throat. As a result, swallowing is more difficult, and choking is more likely. The vertebrae become less dense and the cushions of tissue (disks) between them lose fluid and become thinner, making the spine shorter. Thus, many older people become shorter.
The cartilage that lines the joints tends to thin, partly because of the wear and tear of years of movement. The surfaces of a joint may not slide over each other as well as they used to, and the joint may be slightly more susceptible to injury. Damage to the cartilage due to lifelong use of joints or repeated injury often leads to osteoarthritis, which is one of the most common disorders of later life.
Ligaments, which bind joints together, and tendons, which bind muscle to bone, tend to become less elastic, making joints feel tight or stiff. These tissues also weaken. Thus, most people become less flexible. Ligaments tend to tear more easily, and when they tear, they heal more slowly. These changes occur because the cells that maintain ligaments and tendons become less active.
Muscles and Body Fat
The amount of muscle tissue (muscle mass) and muscle strength tend to decrease. This process is called sarcopenia, which literally means loss of flesh. Loss of muscle mass begins around age 30 and continues throughout life. By age 75, the percentage of muscle mass is typically half of what it was during young adulthood. Muscle mass decreases possibly because the muscles are used less and begin to shrink. Also, the levels of growth hormone and testosterone, which stimulate muscle development, decrease. Muscles cannot contract as quickly because more fast-contracting (fast-twitch) muscle fibers are lost than slow-contracting (slow-twitch) muscle fibers.
Most older people retain enough muscle mass and strength for all necessary tasks. Many older people remain strong athletes. They compete in sports and enjoy vigorous physical activity. However, even the fittest notice some decline as they age.
Regular exercise to strengthen muscles can partially overcome or significantly delay loss of muscle mass and strength. In muscle-strengthening exercise, muscles contract against resistance provided by gravity (as in sit-ups or push-ups), weights, or rubber bands. If this type of exercise is done regularly, even people who have never exercised can increase muscle mass and strength. Conversely, physical inactivity, especially bed rest during an illness, can greatly accelerate the loss. During periods of inactivity, older people lose muscle mass and strength much more quickly than younger people do. For example, to make up for the muscle mass lost during each day of strict bed rest, people may need to exercise for up to 2 weeks.
By age 75, the percentage of body fat typically doubles compared with what it was during young adulthood. Too much body fat can increase the risk of health problems, such as diabetes. The distribution of fat also changes, changing the shape of the torso. A healthy diet and regular exercise can help older people keep body fat from increasing too much.
As people age, the following occur:
A change in vision is often the first undeniable sign of aging.
Changes in the lenses of the eye can cause or contribute to the following:
The pupil of the eye reacts more slowly to changes in light. The pupil widens and narrows to let more or less light in depending on the brightness of the surroundings. A slow-reacting pupil means that older people may be unable to see when they first enter a dark room. Or they may be temporarily blinded when they enter a brightly lit area. Older people may also become more sensitive to glare. However, increased sensitivity to glare is often due to darkened areas in the lens or to cataracts.
Fine details, including differences in shades and tones, become more difficult to discern. The reason is probably a decrease in the number of nerve cells that transmit visual signals from the eyes to the brain. This change affects the way depth is perceived, and judging distances becomes more difficult.
Older people may see more tiny black specks moving across their field of vision. These specks, called floaters, are bits of normal fluid in the eye that have solidified. Floaters do not significantly interfere with vision. Unless they suddenly increase in number, they are not a cause for concern.
The eyes tend to become dry. This change occurs because the number of cells that produce fluids to lubricate the eyes decreases. Tear production may decrease.
The appearance of the eyes changes in several ways:
Most changes in hearing are probably due as much to noise exposure as to aging. Exposure to loud noise over time damages the ear's ability to hear. Nonetheless, some changes in hearing occur as people age, regardless of their exposure to loud noise.
As people age, hearing high-pitched sounds becomes more difficult. This change is considered age-associated hearing loss (presbycusis). For example, violin music may sound less bright.
The most frustrating consequence of presbycusis is that words become harder to understand. As a result, older people may think that other people are mumbling. Even when other people speak more loudly, older people still have difficulty understanding the words. The reason is that most consonants (such as k, t, s, p, and ch) are high-pitched, and consonants are the sounds that help people identify words. Because vowels are lower-pitched sounds, they are easier to hear. So older people may hear “Ell me exaly wha you wan oo ee,” rather than “Tell me exactly what you want to keep.” To help, other people need to articulate consonants more clearly, rather than simply speak louder. Understanding what women and children say may be more difficult than understanding what men say because most women and children have higher-pitched voices. Gradually, hearing lower pitches also becomes more difficult.
Many older people have more trouble hearing in loud places or in groups because of the background noise. Also, earwax, which interferes with hearing, tends to accumulate more.
Mouth and Nose
Generally, when people are in their 50s, the ability to taste and smell starts to gradually diminish. Both senses are needed to enjoy the full range of flavors in food. The tongue can identify only five basic tastes: sweet, sour, bitter, salt, and a relatively newly identified taste called umami (commonly described as meaty or savory). The sense of smell is needed to distinguish more subtle and complex flavors (such as raspberry).
As people age, taste buds on the tongue decrease in number and sensitivity. This change affects tasting sweet and salt more than bitter and sour. The ability to smell diminishes because the lining of the nose becomes thinner and drier and the nerve endings in the nose deteriorate. However, the change is slight, usually affecting only subtle smells. Because of these changes, many foods tend to taste bitter, and foods with subtle smells may taste bland.
The mouth tends to feel dry more often, partly because less saliva is produced. Dry mouth further reduces the ability to taste food.
As people age, the gums recede slightly. Consequently, the lower parts of the teeth are exposed to food particles and bacteria. Also, tooth enamel tends to wear away. These changes, as well as a dry mouth, make the teeth more susceptible to decay and cavities (caries) and thus make tooth loss more likely.
With aging, the nose tends to lengthen and thin, and the tip tends to droop.
The skin tends to become thinner, less elastic, drier, and finely wrinkled. However, exposure to sunlight over the years greatly contributes to wrinkling and to making the skin rough and blotchy. People who have avoided exposure to sunlight often look much younger than their age.
The skin changes partly because the aging body produces less collagen (a tough, fibrous tissue that makes skin strong) and elastin (which makes skin flexible). As a result, the skin tears more easily.
The fat layer under the skin thins. This layer acts as a cushion for the skin, helping protect and support it. The fat layer also helps conserve body heat. When the layer thins, wrinkles are more likely to develop, and tolerance for cold decreases.
The number of nerve endings in the skin decreases. As a result, people become less sensitive to pain, temperature, and pressure, and injuries may be more likely.
The number of sweat glands and blood vessels decreases, and blood flow in the deep layers of the skin decreases. As a result, the body is less able to move heat from inside the body through blood vessels to the surface of the body. Less heat leaves the body, and the body cannot cool itself as well. Thus, the risk of heat-related disorders, such as heatstroke, is increased. Also, when blood flow is decreased, the skin tends to heal more slowly.
The number of pigment-producing cells (melanocytes) decreases. As a result, the skin has less protection against ultraviolet (UV) radiation, such as that from sunlight. Large, brown spots (age spots) develop on skin that has been exposed to sunlight, perhaps because the skin is less able to remove waste products.
The skin is less able to form vitamin D when it is exposed to sunlight. Thus, the risk of vitamin D deficiency increases.
Brain and Nervous System
The number of nerve cells in the brain typically decreases. However, the brain can partly compensate for this loss in several ways:
Levels of the chemical substances involved in sending messages in the brain change. Most decrease, but some increase. Nerve cells may lose some of their receptors for messages. Blood flow to the brain decreases. Because of these age-related changes, the brain may function slightly less well. Older people may react and do tasks somewhat more slowly, but given time, they do these things accurately. Some mental functions—such as vocabulary, short-term memory, the ability to learn new material, and the ability to recall words—may be subtly reduced after age 70.
After about age 60, the number of cells in the spinal cord begins to decrease. Usually, this change does not affect strength or sensation.
As people age, nerves may conduct signals more slowly. Usually, this change is so minimal that people do not notice it. Also, nerves may repair themselves more slowly and incompletely. Therefore, in older people with damaged nerves, sensation and strength may be decreased.
Heart and Blood Vessels
The heart and blood vessels become stiffer. The heart fills with blood more slowly. The stiffer arteries are less able to expand when more blood is pumped through them. Thus, blood pressure tends to increase.
Despite these changes, a normal older heart functions well. Differences between young and old hearts become apparent only when the heart has to work hard and pump more blood—for example, during exercise or an illness. An older heart cannot speed up as quickly or pump as fast or as much blood as a younger heart. Thus, older athletes are not able to perform as well as younger athletes. However, regular aerobic exercise can improve athletic performance in older people.
Muscles of Breathing and the Lungs
The muscles used in breathing, such as the diaphragm, tend to weaken. The number of air sacs (alveoli) and capillaries in the lungs decreases. Thus, slightly less oxygen is absorbed from air that is breathed in. The lungs become less elastic. In people who do not smoke or have a lung disorder, these changes do not affect ordinary daily activities, but these changes may make exercising more difficult. Breathing at high altitudes (where there is less oxygen) may also be harder.
The lungs become less able to fight infection, partly because the cells that sweep debris containing microorganisms out of the airways are less able to do so. Cough, which also helps clear the lungs, tends to be weaker.
Overall, the digestive system is less affected by aging than most parts of the body. The muscles of the esophagus contract less forcefully, but movement of food through the esophagus is not affected. Food is emptied from the stomach slightly more slowly, and the stomach cannot hold as much food because it is less elastic. But in most people, these changes are too slight to be noticed.
Certain changes cause problems in some people. The digestive tract may produce less lactase, an enzyme the body needs to digest milk. As a result, older people are more likely to develop intolerance of dairy products (lactose intolerance). People with lactose intolerance may feel bloated or have gas or diarrhea after they consume milk products.
In the large intestine, materials move through a little more slowly. In some people, this slowing contributes to constipation.
The liver tends to become smaller because the number of cells decreases. Less blood flows through it, and liver enzymes that help the body process drugs and other substances work less efficiently. As a result, the liver may be slightly less able to help remove drugs and other substances from the body. And the effects of drugs—intended and unintended—last longer.
Kidneys and Urinary Tract
The kidneys tend to become smaller because the number of cells decreases. Less blood flows through the kidneys, and at about age 30, they begin to filter blood less well. As years pass, they may remove waste products from the blood less well. They may excrete too much water and too little salt, making dehydration more likely. Nonetheless, they almost always function well enough to meet the body's needs.
Certain changes in the urinary tract may make controlling urination more difficult:
These changes are one reason that urinary incontinence (uncontrollable loss of urine) becomes more common as people age.
In women, the urethra (the tube through which urine leaves the body) shortens, and its lining becomes thinner. The decrease in the estrogen level that occurs with menopause may contribute to this and other changes in the urinary tract.
In men, the prostate gland tends to enlarge. In many men, it enlarges enough to interfere with the passage of urine and to prevent the bladder from emptying completely. As a result, older men tend to urinate with less force, to take longer to start the stream of urine, to dribble urine at the end of the stream, and to urinate more often. Older men are also more likely to be unable to urinate despite having a full bladder (called urinary retention).
The effects of aging on sex hormone levels are more obvious in women than in men. In women, most of these effects are related to menopause, when the levels of female hormones (particularly estrogen) decrease, menstrual periods end permanently, and pregnancy is no longer possible. The decrease in female hormone levels causes the ovaries and uterus to shrink. The tissues of the vagina become thinner, drier, and less elastic (a condition called atrophic vaginitis).
The breasts become less firm and more fibrous, and they tend to sag. This change makes finding lumps in the breasts more difficult.
Some of the changes that begin at menopause (such as lower hormone levels and vaginal dryness) may interfere with sexual activity. However, for most women, aging does not greatly detract from enjoyment of sexual activity.
In men, changes in sex hormone levels are less sudden. Levels of the male hormone testosterone decrease, resulting in fewer sperm and a decreased sex drive (libido), but the decrease is gradual. Although blood flow to the penis tends to decrease, many men can have erections and orgasms throughout life. However, erections may not last as long, may be slightly less rigid, or may require more stimulation to maintain. A second erection may require more time. Erectile dysfunction (impotence) becomes more common as men age.
The levels and activity of some hormones, produced by endocrine glands, decrease.
For most people, the changes in the endocrine system have no noticeable effect on overall health. But in some, the changes may increase the risk of health problems. For example, the changes in insulin increase the risk of type 2 diabetes.
The amount of active bone marrow, where blood cells are produced, decreases. Therefore, fewer blood cells are produced. Nonetheless, the bone marrow can usually produce enough blood cells throughout life. Problems may occur when the need for blood cells is greatly increased—for example, when anemia or an infection develops or bleeding occurs. In such cases, bone marrow is less able to increase its production of blood cells in response to the body's needs.
The cells of the immune system act more slowly. These cells identify and destroy foreign substances such as bacteria, other infecting microbes, and probably cancer cells. This immune slowdown may partly explain several findings associated with aging:
Despite the immune system slowdown, autoimmune disorders become more common. With aging, the immune system may become less able to distinguish the body's own cells from foreign substances that invade the body. Consequently, the immune system may be more likely to attack its own cells—an autoimmune reaction.
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Last full review/revision August 2007 by Richard W. Besdine, MD