Study finds ‘Gradient of Disability’ linked to household income of older adults

Low-income Americans ages 55 to 84 are far more likely than their wealthier peers to feel limited in doing basic physical activities such as climbing stairs and lifting objects, according to a new study. The research, published in the August 17, 2006, issue of The New England Journal of Medicine, shows, for example, that people ages 55 to 64 who are living below the poverty line are six times more likely than the wealthiest group to say they have functional limitations.

The study was conducted by the National Institute on Aging (NIA), part of the National Institutes of Health, in collaboration with the University of California, Berkeley, and the University of Toronto.

The researchers report that those living below the poverty line are the most likely to say they have functional limitations, and, up to age 84, the odds of having such limitations drops with each incremental increase in income. They also note that older people are less likely to report functional limitations with each increase in educational level, a measure that is closely tied to income.

“We found that a ‘gradient of disability’ exists across the full socioeconomic spectrum, as functional limitations proved inversely related to household income,” says senior author Jack M. Guralnik, M.D., Ph.D., chief of the NIA’s Laboratory of Epidemiology, Demography and Biometry.

Improved understanding of the relationship between socioeconomic status and disability is critical as the U.S. population ages, Guralnik notes. The rate of disability decreased 1 to 2 percent annually during the 1980s and 1990s, when trends were last reported, and the rate of decline was smaller among those in the poorest socioeconomic groups.

Guralnik and co-authors Meredith Minkler, D.P.H., University of California, Berkeley, and Esme Fuller-Thomson, Ph.D., University of Toronto, analyzed data for more than 335,000 community-dwelling people 55 and older who participated in the Census 2000 Supplementary Survey. Nearly one in four respondents reported having a functional limitation, defined as a long-lasting condition that substantially limits one or more basic physical activities, such as walking, climbing stairs, reaching, lifting or carrying.

Functional limitation differences by income level were evident among those 55 to 64 years, 65 to 74 years, and 75 to 84 years, but differed more dramatically in the younger age groups. Among all respondents under age 85, even those whose incomes were at six times the poverty threshold had significantly higher odds of reporting functional limitations, compared with the wealthiest group.

The poverty threshold in 2000, the year the data were collected, was $8,259 for a person age 65 or older who lived alone and $17,761 for a four-person household. The highest income category used in the analysis — 700 percent or more of the poverty line — began at $57,813 for an older adult living alone and $124,327 for a four-person household.

The research was supported by the Retirement Research Foundation and the NIA. The NIA leads the federal effort supporting and conducting research on aging and the medical, social and behavioral issues of older people. For more information on research and aging, go to www.nia.nih.gov. Publications on research and on a variety of topics of interest on health and aging can be viewed and ordered by visiting the NIA Web site, or can be ordered by calling toll free 1-800-222-2225.

The National Institutes of Health (NIH) — The Nation's Medical Research Agency — includes 27 Institutes and Centers and is a component of the U.S. Department of Health and Human Services. It is the primary federal agency for conducting and supporting basic, clinical and translational medical research, and it investigates the causes, treatments, and cures for both common and rare diseases. For more information about NIH and its programs, visit www.nih.gov.