Absorption of nutrients: As people age, the amount of water in the body decreases. As a result, the body's ability to absorb water-soluble nutrients, such as vitamin C, is reduced. This also means that there is less saliva and lubricating fluids, such as vaginal secretions.

In patients who are older than 65 years old, the intestines cannot absorb calcium from the diet as well. As a result, the body produces parathyroid hormone, which stimulates the body to take some of the calcium from bones and put it in the bloodstream. This can lead to osteoporosis, a condition in which the bones become hollow and brittle.

Digestion: As people age, less stomach acid is produced. The body uses stomach acid to break down foods. Therefore, elderly patients may have difficulty digesting foods.

Fertility and hormonal changes: As females age, they are less likely to become pregnant. This gradual decline in fertility usually starts very subtly in the late 20s to age 35. Once a female goes through menopause, she is no longer able to have a baby. Most females go through menopause when they are 40 years old or older. Common symptoms of menopause include hot flashes, irritability, vaginal dryness, mood swings, anxiety, difficulty concentrating, loss of sex drive, weight gain, depression, and tender breasts. After menopause, women have an increased risk of developing osteoporosis, a condition that causes the bones to become hollow and brittle. This is because the lower levels of estrogen in the body accelerate bone loss.

As males age, they tend to experience a decrease in their sex hormone, which is called testosterone. This process is called andropause. Most males go through andropause when they are between the ages of 40 and 55 years old. Common symptoms of andropause include fatigue, depression, hot flashes, night sweats, infertility, decreased sex drive, and erectile dysfunction. Erectile dysfunction, also called impotence, occurs when a male is unable to achieve or maintain an erection.

Incontinence: As people age, they are more likely to experience a condition called incontinence. This occurs when a patient is unable to control urination or defecation.

Physical characteristics: As humans age, their hair typically turns gray or white. Some individuals (male and female) may experience hair loss or thinning.

The skin may become wrinkled or have beige-colored spots, which are commonly called age spots. Some areas of the skin, such as under the eyes or under the chin, may sag.

As people age, fat is more likely to increase while muscle decreases. In general, fat is most likely to accumulate in the thighs and stomach. Researchers estimate that the proportion of fat to muscle may increase by as much as 30% with age. This is because the body's ability to remove fats from the body is limited in elderly people. Therefore, more fats, including cholesterol, are stored in the body.

Protein formation, which is reduced, leads to shrinkage in muscle mass and decreased bone formation. Therefore, reduced protein formation may contribute to the development of hollow, brittle, bones. Muscle strength of coordination lessens over time. As a result, people tend to lose mobility, agility, and flexibility as they age.

Body weight typically declines after the age of 55 due to the loss of lean tissue, water, and bone density.

Senses: Hearing, especially the ability to hear high-pitched tones, declines with age.

The ability to smell and taste also declines with age.

Vision generally declines with age. An estimated 42% of people ages 52-64 experience presbyopia, which describes a reduced ability to focus on close-up objects. An estimated 73% of people ages 65-74 and, and 92% of people older than 75, experience presbyopia.

Removing wastes from the blood: Over time, the liver and kidneys, which are responsible for filtering wastes and toxins from the blood, become less efficient. As a result, drugs that are broken down by liver are not inactivated as quickly in the elderly as they are in younger patients. This means that elderly patients may require lower dosages of some medications in order to prevent side effects from occurring. The changes in the kidneys may reduce the patient's ability to urinate and increase the amount of water retained in the body.

General: In general, specific tests are not needed to diagnose aging. Individuals, especially elderly patients, should visit their doctors annually. If the patient's health is regularly monitored, preventative steps can be taken to treat or slow the signs and symptoms of aging. Individuals should also visit the eye doctor annually, especially if they drive or operate heavy machinery, including a car.

Erectile dysfunction: After a physical examination, several tests are available to determine the cause of erectile dysfunction.

A complete blood count may be taken to determine if the patient has low levels of iron in the blood. Low levels of iron may lead to erectile dysfunction.

A blood test may also be performed to determine whether or not high levels of fat in the blood are causing the condition.

Low levels of sex hormones, including testosterone, may also indicate erectile dysfunction.

A duplex ultrasound, which takes pictures of the penis, may also be performed. An ultrasound helps the healthcare provider evaluate blood flow to the penis. It can detect leaking arteries, hardened or blocked arties, or tissue scarring, which may be causing erectile dysfunction.

Hearing: If hearing loss is suspected, a healthcare provider may recommend a specialized doctor called an audiologist. The audiologists will ask questions about the patient's medical history and perform a hearing test called an audiogram to determine the severity of hearing loss. During an audiogram, the patient is exposed to various sounds that have different pitches and frequencies.

Menopause: If it is suspected that a patient is going through menopause, a blood sample may be taken to measure the amount of follicle stimulating hormone. Patients who have high levels of the hormone (50 international units of follicle stimulating hormone per liter of blood or more) have undergone menopause.

Osteoporosis: A bone density test is used to diagnose osteoporosis. A dual energy X-ray absorptiometry (DEXA) takes pictures of the bones in the body and calculates their density. If a DEXA machine is not available, bone density scans can also be done with a dual photon absorptiometry and computerized tomography (CT) scan.

The results are reported as either a T-score or Z-score. A T-score compares the patient's bone density to healthy young women, while a Z-score compares the patient's bone density to other people of the same age, gender, and race. In either score, a negative number means that the patient has less dense bones than normal. Scores from 0 to -1 mean that the patient has borderline bone mass. The patient should repeat the test in two to five years to monitor the condition. If the patient's T-score ranges from -1 to 2.5, he/she has low bone mass and is at risk for developing osteoporosis. If the patient's T-score is lower than -2.5, osteoporosis is diagnosed. These patients should have their bone density tested every year or two.

As individuals age, they have an increased risk of developing many diseases and serious health problems, which may be fatal. Older individuals have an increased risk of developing Alzheimer's disease, stroke, heart attack, osteoporosis, diabetes mellitus, Parkinson's disease, arthritis, and eye diseases, such as cataracts or glaucoma.

General: There are several theories as to why the body loses functioning as it ages. Researchers believe that several factors may be involved.

Cross-linking theory: The cross-linking theory of aging is based on the observation that as individuals age, the proteins, DNA, and other molecules in the body develop inappropriate attachments, or cross-links, to one another. These unnecessary links decrease the mobility of protein and other important molecules in the body. When proteins become damaged or are no longer needed, an enzyme called protease destroys them. However, cross-linkages prevent protease from doing its job. As a result, dysfunctional and unneeded proteins remain in the body and can cause damage.

For instance, cross-linking of the skin protein called collagen has been show to be partly responsible for wrinkled skin. Cross-linking proteins in the lens of the eye has also been shown to cause age-related cataracts. In addition, it has been suggested, but not proven, that cross-linking of proteins in the walls of arteries or the kidneys may be partly responsible for hardening of the arteries (atherosclerosis) and age-related kidney dysfunction.

Although many scientists agree that cross-linking plays a role in aging, there is not enough scientific evidence to confirm that this process is a primary cause of aging.

Free radical theory: The most common theory of aging is called the free radical theory. Many researchers believe that molecules, called free radicals, damage the body's tissues. Free radicals are produced when the body fights against infections. Although free radicals are needed for the body to produce energy, maintain immunity, transmit nerve signals, produce hormones, and contract muscles, they may also contribute to the process of aging.

Free radical damage begins at birth and continues through adulthood. However, when individuals are young, the effects are minimal because the body has many different ways to repair and replace cells to maintain proper functioning. As individuals age, the damage caused by free radicals increases.

Studies have shown that free radicals attack the structures of the body cells and create substances called lipofuscins. When lipofuscins build up in the body, they show up as darks spots on the skin, which are commonly called age spots. Lipofuscins also interfere with the body's ability to repair damage cells and reproduce new ones. As a result, lipofuscins lead to decreased energy levels and they prevent the body from building muscle mass. They also destroy enzymes that are needed for daily functioning.

Studies have also shown that free radicals attack substances in the body called elastin and collagen. These substances help keep the skin smooth, moist, and flexible. As a result, free radicals may cause changes in the appearance of the skin, such as folds or wrinkles.

Genetic theory: It has been suggested that an individual's genetic makeup regulates the rate at which he/she ages. This is called the telomerase theory of aging. However, it does not necessarily mean that patients will live to be the same age as their parents. This is because many other factors, including diet and lifestyle, may influence a person's internal biological clock.

Telomeres are proteins on the ends chromosomes that carry genetic information. Every time a cell divides in the body the telomeres shorten. The shortening of telomeres is believed to cause cellular damage because the cell is unable to make a correct copy of itself. Over time, this process leads to cellular dysfunction, aging, and death.

Wear and tear theory: According to the wear and tear theory of aging, tissues and organs eventually die after years of damage. An individual's genetic makeup (DNA) sustains repeated damage from toxins, radiation, and ultraviolet light throughout the course of a lifetime. Although the body can repair DNA damage, not all of those repairs are accurate or complete. As a result, damage slowly accumulates over time.

For instance, one study evaluated the effect of a lifetime of exposure to stress hormones, such as cortisol. The body produces cortisol in response to physical and emotional stress. Researchers found that the amount of cortisol in the body rises with age. Although cortisol levels decline at night in younger adults, the levels do not fall as far in older adults. The researchers concluded that the increased levels of cortisol might be the result of wear and tear of lifelong exposures to stress.