Current Trends Comorbidity of Chronic Conditions and Disability among Older Persons -- United States, 1984

Although the coexistence of chronic conditions (i.e., comorbidity) is considered common in the older population, there has been little systematic evaluation of the prevalence, patterns, and impact of comorbidity in representative populations (1). Data from the Supplement on Aging (SOA) to the 1984 National Health Interview Survey were analyzed to evaluate the prevalence and impact of comorbidity.

The National Health Interview Survey, conducted by CDC's National Center for Health Statistics, is a continuing survey of the civilian noninstitutionalized population of the United States. In 1984, all respondents aged greater than or equal to 65 years and a 50% sample of those aged 55-64 years were asked to also respond to questions on the SOA. The SOA was designed to collect information about chronic conditions, physical limitations, and other health-related and social information about middle-aged and older persons (2). In total, 16,148 interviews were conducted. This report presents results for the 13,807 persons aged greater than or equal to 60 years, representing an estimated U.S. population of 37,256,000 in this age group in 1984.

Emphasis was placed on nine common chronic conditions in the population aged greater than or equal to 60 years, including: arthritis, present in 49.0%; hypertension, 41.8%; cataracts,* 19.9%; heart disease,** 14.0%; varicose veins, 9.9%; diabetes, 9.5%; cancer (except nonmelanoma skin cancer), 6.6%; osteoporosis/hip fracture, 5.5%; and stroke, 5.4%.

The proportion of the population greater than or equal to 60 years of age with two or more of the nine chronic conditions increased with age and, for each age group, was higher for women than for men (Table 1). For persons aged greater than or equal to 80 years, 70% of women and 53% of men had two or more of the nine conditions.

Prevalence of comorbidity is directly related to the prevalence of each of the individual conditions. Hypertension and arthritis, the two conditions with the highest prevalence, co-occurred in 24.1% of persons greater than or equal to 60 years of age; cataract and arthritis were both reported by 11.7% (Figure 1). The remaining six pairs of the most common comorbid conditions had coprevalences that ranged from 5.5% to 9.6%.

If the prevalences of two conditions are assumed to be independent, their expected coprevalence is the product of their individual prevalence rates. However, for each of the eight most common pairs of conditions, the observed comorbidity exceeded the expected (Table 2). Except for the comorbidity of cataract with hypertension in men, each of these increases was statistically significant (p less than 0.001, adjusted for the complex sampling design).

Respondents were asked if they received assistance with six activities of daily living: getting in and out of bed or chair, walking, using the toilet, bathing or showering, dressing, and eating. The percentage of men and women receiving assistance with one or more of these activities increased directly with the number of chronic conditions (Table 3). Reported by: JM Guralnik, MD, AZ LaCroix, PhD, DF Everett, MS, National Institute on Aging, National Institutes of Health. Office of Vital and Health Statistics Systems, National Center for Health Statistics; Office of the Director, Center for Chronic Disease Prevention and Health Promotion, CDC.

Editorial Note

Editorial Note: Analysis of the 1984 SOA data indicates that the prevalence of comorbidity of chronic conditions in the noninstitutionalized older population is substantial. Comorbidity prevalence rates for the nine chronic conditions are highest for women, increasing from 45% in persons aged 60-69 years to 70% in persons aged greater than or equal to 80 years.

For the most commonly reported pairs of conditions, the observed coprevalence is consistently higher than predicted by their independent distributions. The explanation may be apparent for two of these pairs: coronary heart disease and hypertension (a known risk factor for coronary heart disease) and hypertension and diabetes, which share overweight as an underlying risk factor. For the other six pairs of conditions, however, increased rates of coprevalence were not anticipated. Although these are modest increases, their impact may be substantial. For example, the independent distributions of hypertension and arthritis predict that 7.6 million persons aged greater than or equal to 60 years have both conditions. However, the SOA data indicate that this pair of conditions occurred in approximately 9 million persons--1.4 million more than expected.

At least three factors may contribute to the increase in observed coprevalence for conditions not generally recognized as being associated. First, those persons with one condition may have more contacts with the medical-care system and, therefore, greater likelihood of any second condition being diagnosed. Second, persons who report having one disease may be more likely to report having other diseases. Third, in some persons, genetic, environmental, and behavioral factors may increase general susceptibility to disease, resulting in the occurrence of multiple diseases in the later years of life.

The SOA data also suggest an association between the number of conditions present and the proportion of persons with disability (as assessed by ability to perform activities of daily living). This association was present even though the conditions were not weighted for severity; in addition, the potential impact of these conditions on disability varied considerably (e.g., stroke has a greater potential impact than varicose veins). Despite these important limitations, the number of conditions present may represent a useful measure of the burden of illness on older persons, as reflected by associated disability. Because functional limitations increase with age and number of chronic conditions, comprehensive public health strategies should include disability prevention as well as health promotion and disease prevention.

References

1. Rice DP, LaPlante MP. Chronic illness, disability, and increasing longevity. In: Sullivan S, Lewin ME, eds. The economics and ethics of long-term care and disability. Washington, DC: American Enterprise Institute for Public Policy Research, 1988:9-55.

2. NCHS, Fitti JE, Kovar MG. The supplement on aging to the 1984 National Health Interview Survey. Hyattsville, Maryland: US Department of Health and Human Services, Public Health Service, 1987:DHHS publication no. 87-1323. (Vital and health statistics; series 1, no. 21).

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