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While an in-depth understanding of internal medicine serves as a foundation, proper care of older adults should be complemented by insight into the multidimensional effects of aging on disease manifestations, consequences, and response to treatment. In younger adults, individual diseases tend to have a more distinct pathophysiology with well-defined risk factors; the same diseases in older persons may have a less distinct pathophysiology and are often the result of failed homeostatic mechanisms. Causes and clinical manifestations are less specific and can vary widely between individuals. Therefore, the care of older patients demands an understanding of the effects of aging on human physiology and a broader perspective that incorporates geriatric syndromes, disability, social contexts, and goals of care. For example, care planning for the older patient cannot ignore the influence of life expectancy. In fact, the expected remaining years of life can guide recommendations about appropriate preventive and other long-term interventions, and shape discussions about treatment alternatives.

Demography (Chap. 70) Population aging emerged on a worldwide scale for the first time in history within the last century. Since aging influences many facets of life, governments and societies now face new social and economic challenges that impact health care, as well as family and community responsibilities. Figure 72-1 highlights recent and predicted changes in U.S. population structure. The overall number of children has remained relatively stable, but explosive growth has occurred among older populations. The percentage growth is particularly dramatic among the oldest old. For example, the 80–89-year-old group increased more than threefold between 1960 and 2010 and will increase almost tenfold between 1960 and 2050. Women already outlive men by many years and the sex discrepancy in longevity is projected to increase further in the future.

Figure 72-1

Change in the structure of the U.S. population between 1960 and 2050. (From United Nations World Population Prospects: The 2008 Revision,

Population aging occurs at different rates in varying geographic regions of the world. Over the last century, Europe, Australia, and North America have had the populations with the greatest proportions of older persons, but Asia and South America are aging rapidly, with a population structure that will resemble the "older" countries by around 2050 (Fig. 72-2). Among older persons, the oldest old (those older than age 80 years) are the fastest growing segment of the population (Fig. 72-3), and the pace of aging is projected to accelerate in most countries in the next 50 years. There is no evidence that the rate of population aging is decreasing.

Figure 72-2

Population aging in different geographic regions. (From United Nations World Population Prospects: The 2008 Revision,

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