Aging, Epidemiology of

The epidemiologic study of older people in the community has been pursued for many years. Although there is probably nothing unique about the application of epidemiologic methods to older populations, there are many important differences and special issues that merit separate consideration. Vital records, census counts, and demographic studies have documented the increased longevity of populations in nearly all developed countries over the past half century and the growth of the numbers of older persons. The increase in older populations has led to new opportunities for more detailed exploration of health and disease occurrence, risk factors for morbidity and mortality, and health outcomes. The growth in numbers of older persons has also caused a public health mandate for improved surveillance and control of important conditions in those populations, both in the community and in institutional settings. This entry examines differences between epidemiologic studies of older adults compared with other age groups. It also discusses issues in conducting population surveys among older persons.

There are a number of general differences in the epidemiologic study of older populations from young and middle-aged groups, including differences in the clinical manifestations of disease and conditions among older persons, alterations in medical practice, and variations of the ‘natural history’ trajectories and outcomes. As a generalization, diseases that occur in young and middle-aged persons are single entities and have few complicating secondary conditions, at least early in their history. The natural conditions occurring in youth and middle age tend to have more genetic influence. Noninvolved bodily systems tend to be generally intact, and most treatments relate to the primary condition. Social support systems for coping with these conditions are more often well developed. In contrast, health and disease states among older people differ in many ways.

1. Multiple, Simultaneous Health Conditions (Comorbidity). The presence of multiple health conditions and physiological dysfunctions is the rule in older people, whether an acute or severe disease is present or not. This necessitates that epidemiologic assessment of older people contain detailed information on a wide range of organ systems. Otherwise, many will not be detected. Having one condition may lead to increased medical surveillance for other conditions (‘detection bias’), thus altering the natural history of the latter condition. Also, the presence of comorbidity requires that studies of disease causation consider how the conditions other than the one of primary interest affect the risk factors. For example, if [Page 12]one is exploring the role of tobacco use in Condition X, it is important to know if comorbid Condition Y, which may have clinically emerged earlier, had an effect on smoking habits.

2. Increased Prevalence of Common Clinical Signs and Symptoms. Surveys of older persons reveal that prevalence rates for common clinical signs and symptoms are higher than in younger populations, having several implications for understanding health status. First, even if there is no obvious major acute or chronic illness present, these clinical phenomena may negatively affect personal comfort and function. Pain syndromes are notoriously present at high rates and have important consequences. Chronic leg cramps is an important, if less well-studied, example. Another implication of common signs and symptoms is that there may be a loss of diagnostic specificity. For example, if dry and itching skin is a potential indicator of clinical or subclinical hypothyroidism, possibly leading to a diagnostic inquiry, a prevalence rate of 40% among older persons may preclude those skin symptoms as potential diagnostic indicators, because relevant thyroid conditions are much less common. This then becomes a challenge for the clinician and the epidemiologist, because there may be less intense diagnostic activity for thyroid disease.

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