“There is no difference between a young man and an old man as long as they are both sitting.” –Mark Twain
Normal aging in the absence of disease is a remarkably benign process. Physiologically, aging is essentially the gradual but steady erosion of the organ systems and of the body’s built-in capacity to repair itself. In many cases, this erosion is evident only during periods of maximal exertion or stress and many people carry on with their normal daily activities well into old age.
Since none of us can live forever, the overall goal is to keep the body in working order until everything falls apart at once at the end of life. Eventually, the body reaches a critical point, usually in very advanced age, when minor problems cannot be overcome and result in the person’s death in a relatively short time. For example, a urinary tract infection is usually just a nuisance to a college student but may be the harbinger of serious decline in an 85-year-old person. Consequently, a healthy person who is aging normally will often experience serious illness and weakening only in the last period of life. Exceptions to this ideal aging process are typically the result of diseases such as heart disease or cancer.
This series of four posts will review the main physical changes that you can expect from your aging body. Some of these changes may affect how others perceive you or how you perceive yourself but otherwise have little impact on your quality of life. Some may bring discomfort or inconvenience that is generally manageable if you are prepared and willing to make accommodations. Others can lead to more substantial impacts on your quality of life.
Changes in Height
We all lose height as we age but there is great variability both in the age of onset and the rate of loss. On average, most people lose about two inches by age 80. Some of this loss happens in the torso due to changes in posture, changes in the growth of vertebrae, a forward bending of the spine, and the compression of the discs between the vertebrae. Changes in the legs and feet also contribute to this loss, including increased curvature of the hips and knees, decreased joint space in the extremities and flattening of the arches in the feet.
Changes in Body Composition
Aging causes important changes in body composition and in the structural elements of tissues. The proportion of the body that is made up of fat increases on average from 14 percent to 30 percent between the ages of 25 and 75. At the same time, we experience a decrease in total body water (mainly the water outside our cells called extracellular water), a substantial loss of lean muscle mass and a slight decrease in bone and viscera. Specific organs show noticeable losses: the liver and kidneys, for example, lose approximately a third of their weight between ages 30 and 90. On the other hand, the prostate gland doubles in weight between ages 20 and 90.
These changes seem to be influenced by hormonal changes. They can have important implications for nutritional planning and the use of medications. For example, a dose of a lipid-soluble drug such as diazepam (Valium®) will remain in the body of an older person much longer than it stays in a younger person because the older person’s body contains more fat.
Changes in Skin
Skin changes such as wrinkling are one of the physical alterations most readily associated with aging. It may surprise you that the outer layer of the skin, the stratum corneum, changes very little as we age. The main changes occur at a deeper level. Collagen, a basic chemical building block of skin and connective tissue, decreases with age. Its structure also changes. The collagen fibers in younger skin exhibit an orderly arrangement similar to fibers in a rope. These fibers become coarser and more random with aging, eventually resembling a mass of spaghetti. It is this shift that causes a loss of elasticity and produces wrinkles.
In addition, as we age the contact area decreases between the dermis, the inner skin layer, and the epidermis, the layer that covers it. There are also reductions in the number of deeper basal cells and pigment-producing cells, the melanocytes, as well as Langerhans’ cells, those that come from the bone marrow and provide assistance to the immune system. The reduction of these cells is striking in skin that has been exposed to sunlight and is thought to contribute to the development of sun-related skin cancers, though their effect on normal aging of skin is not known.
Changes in Hair
Hair changes play a prominent role in how we perceive aging but otherwise have very little impact on one’s quality of life. Hair graying results from a progressive loss of pigment cells (melanocytes) from the hair bulbs. Although graying of hair on the head can occur at relatively young ages, the graying of hair in the armpit is thought to be one of the most reliable signs of aging.
There are also age-associated changes in hair growth rate and the amount of hair on various parts of the body. The number of hair follicles on the scalp decrease with age, and the growth rate of scalp, pubic and armpit hair tends to decline. Elderly men often experience an increased growth of eyebrow, nostril and ear hair, and elderly women sometimes see an increased growth of facial hair, possibly because of hormonal changes.
Changes in Muscles and Bones
Most people lose a substantial amount of muscle as they age. Broadly speaking, muscles decrease in strength, endurance, size, and weight relative to total body weight. However, the late onset of these changes and their unpredictable rate of appearance suggest that they may not be due to aging but rather one due to inactivity, nutritional deficiency, disease or other long-standing conditions. Curiously, both the diaphragm and the heart, two muscles that work continuously throughout life, appear to be relatively unchanged by aging.
We also experience changes in cartilage, the flexible, cushioning substance that provides the lubricating surface of most joints. Decreased water content and changes in cartilage structure and chemistry may reduce the ability for our cartilage to bounce back during repetitive stress as we grow older.
Bone loss is a universal aspect of aging that occurs at highly individual rates. While bone growth and remodeling occur throughout life, as we age the growth of bone slows and the bone begins to thin and become more porous. The internal latticework of bones also loses its horizontal supports, which significantly compromises its strength.
The skull, on the other hand, appears to thicken with age. This growth is most apparent deep in the skull and in the frontal sinuses. Bone growth also has been demonstrated well into advanced age in the ribs, the fingers, and the femur. Changes in the hip may also be important because growth in the midportion of the bone results in a wider but weaker bone.
Conditioning, nutrition, hormones and disease have a significant influence on the degeneration of muscles and bones as we age. Conditioning is the most significant because disuse or underuse accelerates the declines in bone and muscle structures. Previous posts have explored how exercise and nutrition can help you maintain strength in the muscles and other bodily systems.