Epidemiology of Aging

Aging and Health Outcomes

Standard categorical diseases represent the most common health outcomes in epidemiological research. Definitions of categorical diagnosed conditions, such as breast cancer and coronary heart disease, are based on the proposition that a standard set of presenting symptoms and signs reflect a single pathological condition. In general, aging is associated with an increase in the incidence and prevalence of categorical diseases. Incidence is defined as the number of new conditions diagnosed in a given population over a given period of time. An incidence rate is the number of new cases of a condition found in a given population over a specific period of time (e.g., calendar year) divided by the number of people in the population at risk for the condition during that time and then multiplied by a standard number, in most cases from 1,000 to 100,000. Prevalence refers to the number of people in a given population alive with the condition over a specific time period. The longer people survive after being diagnosed with a condition, the greater the prevalence and the higher the prevalence rate. Although age-specific incidence and prevalence rates increase for most health conditions, the increase is most pronounced for chronic conditions such as coronary heart disease, stroke, and most forms of cancer.

Research to understand the reasons for the association between aging and disease incidence and prevalence is very important, but aging and disease involves much more. For example, older people are at elevated risk not only for single conditions but also for multiple conditions. Multiple morbidity is defined as the presence of two or more health conditions diagnosed in the same older person. Comorbidity, a related term, is defined as the presence of one or more conditions among people diagnosed with an “index” condition. Results from the National Health Interview Survey indicated that the percentage of people age 60 years and older who reported having two or more of the nine most common conditions increased steadily with age. Specifically, the percentage of women who reported two or more conditions increased from 45% among those 60 to 69 years of age, to 61% among those 70 to 79 years of age, to 70% among those age 80 years and older. Among men, these percentages were 35%,47%, and 53%, respectively. The presence of, and treatment for, multiple conditions may affect the risk of subsequent diseases as well as the presentation of the symptoms of those diseases. The presence of previously diagnosed conditions, including their past and current treatments and monitoring, may affect the nature and interpretation of symptoms for current conditions. It has been observed that conditions such as falls, confusion and urinary incontinence may be the presenting symptoms for a variety of treatable diseases. It has also been reported that a myocardial infarction or a perforated ulcer may occur without pain and that pneumonia and infections may occur without fever.

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