This
article appeared in Aging Today, November/December 1997, copyright American
Society on Aging, 1997. It appeared in the newspaper's Research Today section,
aupported by a grant from the AARP Andrus
Foundation.
Toward Independence: Learning How Chronic Illness Disables Elders
The subtle gravitational pull of chronic illness on an elder's ability to function and remain independent was a surprisingly undercharted region of gerontological research until the past decade.
Only in 1988, for example, were the tiny battery cells known as mitochondrial DNA, microbiologic power cells that transmit 90% of the energy our bodies need to function, linked by scientists to human diseases. In "Mitochondrial DNA in Aging and Disease" in Scientific American's August 1997 issue, DNA research leader Douglas C. Wallace, of the Emory University School of Medicine in Atlanta revealed that mutations in these microscopic cells "may play a role in the aging process and in chronic, degenerative illnesses that become common late in life--such as Alzheimer's disease and various motor disturbances."
The intricacies of cellular science are fascinating, such as how mitochondrial DNA cells are attacked and mutated by voracious toxic by-products called oxygen free radicals in ways that may contribute to both illness and the normal declines of aging (losses in stamina, memory and the senses). Yet they are only part of the complex interrelationship of ailments and physical functioning that remains to be understood. Strides in longitudinal and clinical research have also been made in the past decade. They are helping scientists begin to grasp how preventive and treatment measures can interrupt the linkages between specific chronic ailments and disabilities that may lead to premature institutionalization for elders.
"As the size of the older population grows and life expectancy continues to increase," wrote the National Institute on Aging's (NIA) Jack M. Guralnik and colleagues last year, "treatment and prevention strategies that address the functional consequences of disease and the burden of disability . . . will become increasingly important."
Guralnik, chief of the Epidemiology, Demography and Biometry Office at NIA in Bethesda, Md., coauthored a state-of-the-art review of research literature with colleagues Linda P. Fried and Marcel E. Salive in Annual Review of Public Health, 1996 (17:25 - 46). The article, dryly titled "Disability as a Public Health Outcome in the Aging Population," focused on nearly 100 scientific studies, most published in the past decade, which contributed to the effort to reduce the prevalence of disability in the aging population and "increase the number of years in which older people lead highly functional, independent lives."
The authors reported that about 6.5 million Americans aged 65 or older had problems with mobility or disabilities related to vital activities of daily living (ADLs), such as eating or using the toilet, according to a special survey on disability included in the 1990 United States Census.
They noted that women are particularly affected by disabling conditions. Although studies have shown that older men and women acquire disabilities at about the same rate, more elderly women than men endure with disabilities simply because they live longer than males, even when disabled. The Women's Health and Aging Study revealed that in a typical week, one in three of disabled women surveyed did not leave their neighborhoods, 15% did not exit their homes and 12% stopped using rooms in their homes because of their disabilities.
ELDERS ARE RESILIENT
Guralnik and colleagues stressed in their literature review that although data from numerous studies demonstrate that disability in either ADLs or instrumental activities of daily living (IADLs), such as shopping or cooking, are major predictors of both mortality and other adverse outcomes, from illness to injurious falls, the evidence is clear that older people are resilient.
The authors wrote, "Contrary to the belief that disability progresses in an inexorable downhill course, multiple longitudinal studies have demonstrated that it is not rare for individuals to report less disability in follow-up evaluations" to earlier initial assessments. California's Alameda County Study, for example, found that during a six-year period, 13% of men and 20% of women who reported having disabilities actually improved in functioning.
However, said the Guralnik research overview, evidence shows a diminishing likelihood that an elder can bounce back the longer disability persists. This suggests that more specific and better interventions are needed to give a boost to the many who might recover. The authors stated, though, "Compared to the extensive research devoted to understanding the pathophysiology and risk factors for specific diseases, relatively little work has examined the risk factors for functional decrements in aging."
The authors explain that more study is needed to understand the intricate pathways between disease and disability, the mechanisms by which specific diseases cause disability and how multiple illnesses interact to cause debilitation. Almost a decade ago, they reported, A.B. Ford and colleagues estimated in the Journal of the American Geriatrics Society that arthritis was responsible for 34% of physical disability in elders. Stroke, visual impairment, heart disease and dementia together accounted for about half of disability and the remaining 15% derived from peripheral vascular disease, lung disease, depression, diabetes, hearing impairment and hypertension.
Further, medical science must learn more about the influences of such nondisease factors as social isolation and depression, which may compound the effects of illness. Research has also uncovered evidence of demographic and behavioral effects (for example, smoking and lack of exercise). A 1993 study in the American Journal of Epidemiology, with Guralnik as lead author, found that the loss of mobility was 1.5 times more common among the economically poorest subjects than among the members of the cohort with highest incomes, even after adjusting for "a long list of chronic conditions." Poverty itself needs to be better understood as a contributing factor for disability.
Numerous studies point to a better understanding of the intertwining effects of multiple conditions on disability. For example, in a 1994 study in the Journal of Gerontology: Medical Science, C. Boult and colleagues assessed the effects of four chronic conditions (cerebrovascular disease, arthritis, coronary artery disease and diabetes) on ADL and IADL disability and mortality. During four years, those with none of the conditions stood a 3% chance of becoming disabled and a 4% chance of dying. Elders with all four conditions had a 13% chance of incurring a disability--and nearly one in four died.
Guralnik and colleagues added, "From the standpoint of prevention of disability, targeting particular diseases that act synergistically with other disease in causing disability could be very important in reducing overall population risk of disability."
KEY CHALLENGES
A key challenge for researchers is to find ways to measure changes in disability more accurately than customary self-reports by older patients or proxy reports by caregivers. For example, Mark E. Williams and colleagues at the University of North Carolina have examined timed manual performance tasks, such as opening and closing padlocks, as part of a comprehensive geriatric assessment approach aimed at predicting disability.
Although self-reported disability has "stood the test of time" as a reliable gauge of disability, wrote Guralnik and coauthors, many questions remain about performance measures, such as their cost-effectiveness and how well they reflect performance of tasks by elders done at home as opposed to a laboratory setting. Eventually, said the authors, "In the clinical setting, these measures may work well to establish the link between specific disease and specific disabilities."
A related challenge for researchers is learning to spot disability before it becomes full-blown. Such a "preclinical" state of functional loss has only been hypothesized, but evidence is increasing that it exists. In a 1995 study in the New England Journal of Medicine, a team led by Guralnik found that performance by nondisabled older individuals in tests of gait (walking) velocity, balance and ability to rise from a chair "was highly predictive of the subsequent onset, one and four years later, both of ADL disability and disability in mobility." They found that elders who tested with the lowest scores "were four to five times more likely to have disability four years later than those with the best scores."
The literature review applauded both continued observational studies, which will help to develop new interventions that can be studied in randomized controlled trials, and the emergence of new treatment approaches using broad-based interventions to reverse the effects of functional impairments resulting from multiple causes.
"What remains to be studied," the authors concluded, "is whether the kinds of interventions that improve aspects of functioning, such as gait, strength and balance, can ultimately prevent or delay the onset of disability and loss of independence." *
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