The increase in the number of older people represents a profound demographic revolution with the potential for impact that will exceed even that of the Industrial Revolution.
The proportion of the world's population over the age of 60 years doubled in the last century and will increase 2-to 3-fold during the first century of this millennium (Fig. 1).
Although aging has been considered largely a crisis for the global economy and health care services, the potential capacity for excellent health in older age, allowing older people to make a positive contribution to society should be recognized.
Compression of morbidity and substantive positive cohort effects mean that it is almost certainly misleading to extrapolate from current levels of disease and disability to future generations of older people, potentially upending doomsday economic scenarios.
Fig. 1. Percentage of the world population aged 60 years or older over the last century and projections for the next century
Aging is a universal process whose manifestations are familiar and unambiguous, and old age in humans and even animals can be recognized readily after minimal assessment.
Despite this, an accepted definition of aging and a detailed understanding of the biological mechanisms underpinning aging are elusive.
Aging has been defined as the progressive loss of function accompanied by decreasing fertility and increasing mortality and disability.
In addition, aging has dramatic effects on the response to pharmacological, surgical, and rehabilitative interventions.
Altered responses to therapeutic interventions might be considered in any future definitions of aging, since mortality and disability are key indicators of the performance of most therapeutic interventions.
The prevalence of markers of disease, diseases per se, disability consequent on disease, and mortality rate increases exponentially in old age (Fig. 2).
Consequently, old age is considered to be the major risk factor for many, if not most, diseases in developed countries.
For example, representative percentages of people aged 70 years or older with various common chronic diseases are arthritis, 58%; hypertension, 45%; heart disease, 21%; cancer, 19%; diabetes, 12%; and stroke, 9%.
Fig. 2. The relationship between age and the rate of disease
The high prevalence of disease promotes high use of medications in older people.
The prescription of medications is the most frequent therapeutic intervention undertaken by clinicians.
Older people use on average two to five prescription medications on a regular basis, and polypharmacy, defined as the use of five or more medications, occurs in 20 to 40% of this age group.
Although the potential benefits of appropriately prescribed and monitored medications are without question, the hazards and negative outcomes of medications in older people are also well recognized and have received extensive comment.
The incidence of adverse drug reactions correlates with age, and as many as one in five hospital admissions are medication-related in older people.
A recent Norwegian study indicated that adverse drug reactions were the cause of death of 18% of older hospitalized patients.
It is of concern that the very population that receives the most medications may not always have a favorable risk-benefit ratio.
This paradox has occurred in part because there is inadequate evidence and knowledge about the responses of geriatric patients to medications.
Older people are poorly represented in clinical trials, with up to 35% of published trials excluding older people on the basis of age without justification.
Therefore, there is a pressing need to increase the number of older people in clinical drug trials and to increase understanding of the effects of the biological processes of aging on drug action.
Conversely, it has been argued that older people are denied useful pharmacotherapy because of ageist attitudes and unjustified concerns about adverse effects.
Geriatric therapeutics must also take into account specific geriatric diseases (dementia, osteoporosis) and syndromes (falls, gait and balance disturbances, incontinence, failure to cope) and the growing use of antiaging medications.