What Should Be Considered as Normal Ageing Process?

Aging in human is a combination of two ageing processes: development or maturation, and senescence aging or decline. Development or maturation is the positive aspect of aging; humans typically acquire greater wisdom, experience, and expertise in specific fields as they grow older. Senescence aging, on the other hand, refers to the gradual loss over time of the ability of aging cells in body tissues to divide and multiply, the ability of the body to grow, and the ability to maintain good functioning.

Hayflick Limit and The Biology of Aging Cells

The biology of aging can be described at the level of cells and molecules or at the level of an entire organism. On the cellular level, cells in most human tissues eventually lose their ability to divide unless they become cancerous. In the mid-1960s, a biologist named Leonard Hayflick discovered that human cells stop dividing after about 50 or 52 divisions. It is now known that Hayflick limit is the result of the shortening of telomeres—regions of repetitive DNA at the ends of chromosomes—with each successive cell division. The telomeres protect the ends of the chromosomes from damage during cell division; some biologists think that this mechanism evolved as a protection against the unregulated multiplication of cells characteristic of cancer. After Hayflick limit is reached, the aging cells cannot divide again and is said to be senescent. It will continue to exist for some time and gradually enlarge but eventually die.

The relationship of Hayflick limit to the aging of the entire human body is not completely understood as of the early 2000s. Some cells in the human body, such as stem cells, which exist in every tissue, are not affected by Hayflick limit and will continue to reproduce throughout the lifespan. In humans, however, the body begins to enter what is called organismal senescence aging at some point between 20 and 35 years of age. Organismal senescence aging is marked by a reduced ability to respond to stress and by increased susceptibility to disease. Individual differences in the speed of the ageing process at the organismal level are thought to result from a combination of genetic and environmental factors, with genetic factors being more important in determining longevity.

Normal Ageing Process

There is some disagreement among researchers as to which changes in humans over the lifespan represent so-called normal ageing and which represent disease processes. The distinction may sometimes be a matter of statistical distribution; for example, some loss of memory (memory disease)is nearly universal in the elderly and is considered part of normal ageing, while dementia, although more common in the elderly than in younger adults, is still considered a disease process. Another example is glucose intolerance; a certain degree of glucose intolerance is thought to be part of normal ageing process; however, diabetes is still defined as a disease even though type 2 (adult-onset) diabetes is more common in older adults in the early 2000s than it was in 1950.

As of the early 2000s, the following changes in humans are considered normal ageing process:

Changes in height. Humans generally continue to grow taller until they are in their forties but then lose about 2 inches in height by age 80. The reasons for this loss of height include changes in posture, changes in the joints in the feet, and compression of the discs between the vertebrae in the spine.

Changes in weight. Adults generally gain weight until their fifties (in men) and sixties (in women), but gradually lose weight in their seventies and eighties.

Changes in body composition. People generally lose muscle as they age, replacing it with fatty tissue; however, this change can be minimized by regular exercise.

Less effective regulation of various body processes. The ability to regulate and monitor blood pressure, body temperature, response to infection, and the level of fluid in body tissues declines as humans get older.

Slowed reaction to visual or visual impairment in elderly to other stimuli. This change in response time is one reason why older drivers are at increased risk of accidents.

Changes in vision. The ability of the lens in the eye to accommodate (change its focus in seeing objects at different distances) decreases with age.

It is important to note that normal ageing process covers a range of individual responses to the ageing process. Not only do people vary among themselves in their overall rate of aging, but different organ systems may age at different rates within a given individual. For example, one person might have a well-functioning cardiovascular system and severe arthritis, while another might have strong joints and muscles but a weak heart or a visual disorder. As humans age they become less like one another biologically, so that health care regimens need to be individualized.©