Introduction

Aging is a process of gradual maturation. Senescence is the process by which the capacity for cell division and the capacity for growth and function are lost over time, ultimately leading to death.

Aging is thought to have the positive component of development (eg, increased wisdom, experience, and expertise) and the negative component of decline. The term senescence is the most common term for the decline component and refers only to changes that are deleterious.

The changes that occur with aging can be categorized as those that result from aging itself and those that result from diseases, lifestyle, and exposures. Normal aging is sometimes used to refer to changes attributed to aging itself. Usual aging (sometimes also but confusingly referred to as normal aging) refers to the common complex of diseases and impairments that occur in many elderly people. However, this complex is hard to define because people age very differently: Some acquire diseases and impairments, and others seem to escape disease altogether and are said to have died of "old age." Some animals, including certain birds and fish, do not appear to age at all.

Successful (healthy) aging refers to a process by which deleterious effects are minimized, preserving function until senescence makes continued life impossible. People who age successfully avoid experiencing many of the undesirable features of aging and, whether they have a disease or not, remain functional both physically and mentally.

The percentage of community-dwelling people > 65 who report needing assistance with activities of daily living has decreased over the last 2 decades, as has the percentage of people with debilitating disease. One viable explanation for these changes is an increase in the percentage of people who are aging successfully, although there may be other explanations.

Disease vs aging: With aging, many physiologic functions decline. Many of these declines are attributed to aging itself; in other words, they are considered normal, not disease-related. The distinction between normal and disease-related may be clear or may simply be defined by statistical distribution. With presbyopia (decreased accommodation of the lens of the eye), the distinction seems clear because presbyopia occurs in virtually all elderly people and no cause or explanation has been identified other than aging itself. However, with glucose control and cognition, statistical distribution may define the distinction between normal and disease-related. Some degree of glucose intolerance is considered part of normal aging, but diabetes, although very common, is considered a disease. Cognitive decline is nearly universal with aging and is considered normal aging; however, dementia, although common in late life, is considered a disease.

This topic was last updated June 2006.