Mohammed T. Abou-Saleh

CHRONOLOGICAL AND FUNCTIONAL AGEING 73Figure 13.2. Scenarios for change in average burden of populationdisability level, 1997–2050. Compression of morbidity and alternatives13.2. The total length of the bars in this figure represent lifeexpectancy observed for 1997 and projected by the Census Bureaufor 2050. The length of the unshaded segments of the barsrepresents active or disability-free life expectancy, and the shadedareas of the bars represent the average number of years in thedisabled state. In scenario 1, the onset of disability has beenpostponed the same number of years as life expectancy hasincreased, and the number of years spent in the disabled state isunchanged from 1997. In scenario 2, there has been a compressionof morbidity. Finally, in scenario 3, although disability-free lifeexpectancy in 2050 has increased compared with 1997, it has notkept pace with increases in life expectancy and there is anexpansion of population morbidity.A vigorous debate over the prospects for a compression ofmorbidity began with a landmark paper by Fries, in which hemade the claim that the compression of morbidity was inevitablein the coming years 21 . He argued that in all species the maximumlifespan is fixed, that human beings are quickly approaching thislimit, and that with a stable life expectancy any postponement ofdisease and disability would result in a compression of morbidity.Although this logic is correct, others have pointed out that lifeexpectancy is probably not going to reach its maximum level forat least the next half century and we must consider that any of thealternative scenarios depicted in Figure 13.2 are possible in theface of increasing life expectancy.Repeat estimation of active and disabled life expectancy overtime using identical techniques in the same target populationwould allow for a direct assessment of compression of morbidity,but these data are not available. However, disability prevalence,which is not equivalent to disabled life expectancy but reflects across-sectional picture of the proportion of the population that isdisabled, can be estimated, and a great deal of attention has beenfocused on longitudinal trends in disability. In the 1970s there wassome evidence of a rising prevalence of disability, but in the 1980srates appear to have declined 24–26 .For example, Manton et al. 24,27 have reported an averageannual adjusted decline of 1.1% in the prevalence of acomposite measure of severe disability in the population aged65 and over, from the US National Long Term Care Survey forthe period 1982–1994. Freedman and Martin 26 reported similardeclines in a more specific measure of difficulty in walking or useof mobility aids from the Survey of Income and ProgramParticipation: for example, the prevalence of disability definedby this criterion declined during the 10 year study period from30.6% to 27.2% at age 65–79 and at age 80 and over from44.0% to 40.9%. Although there is a scarcity of longitudinaldata from other countries, similar findings have been reported 28with only a few exceptions where rates have probably beenstable.Possible causes of these declines in disability prevalence includeenvironmental changes making daily tasks easier 8 , more intensiveuse of assistive devices 29 and other social changes, includingattitudes to being active in old age. In addition, the proportion ofolder people who have little education (a potent risk factor fordisability) has declined 26,30 . There is also evidence of decliningprevalence of some medical conditions in old age, especiallycardiovascular disease. Health risk avoidance and improveddiagnostic and therapeutic techniques will also have contributed.The future burden of morbidity and disability in the olderpopulation is of great concern to those involved in planning,financing and delivering health care and social services. If currentrates of disabling diseases such as Alzheimer’s disease and hipfracture remain unchanged, the numbers of older people withthese diseases will increase substantially in the next century 31 .Gaining an understanding of factors that have an impact onfunctional aging is critical if we are to reduce the burden ofdisability and achieve a compression of morbidity. Ultimately,effective interventions must be developed to prevent the onset andmitigate the consequences of diseases that lead to much of thedisability in late life.REFERENCES1. Costa PT, McCrae RR. Design and analysis of aging studies. InMasoro EJ, ed. Handbook of Physiology, Section 11: Aging. NewYork: Oxford University Press, 1995.2. Miller RA. When will the biology of aging become useful? Futurelandmarks in biomedical gerontology. J Am Geriatr Soc 1997; 45:1258–67.3. Fried LP, Guralnik JM. Disability in older adults: evidence regardingsignificance, etiology, and risk. J Am Geriatr Soc 1997; 45: 92–100.4. Public Health Service. Healthy People 2000: National HealthPromotion and Disease Prevention Objectives. DHHS Publicationno. (PHS)79-55701. Washington, DC: US Department of Health andHuman Services, Public Health Service, 1990.5. World Health Organization. International Classification ofImpairments, Disabilities, and Handicaps. Geneva: World HealthOrganization, 1980.6. Nagi SZ. An epidemiology of disability among adults in the UnitedStates. Milbank Mem Fund Q 1976; 54: 439–68.7. Institute of Medicine. Committee on a National Agenda forPrevention of Disabilities. Disability in America: Toward a NationalAgenda for Prevention. Pope M, Taylor AR, eds. Washington, DC:Institute of Medicine, National Academy Press, 1991.8. Verbrugge LM, Jette AM. The disablement process. Soc Sci Med1994; 38: 1–14.9. Jette AM, Assmann SF, Rooks D et al. Interrelationships amongdisablement concepts. J Gerontol Med Sci 1998; 53: M395–404.10. Guralnik JM, LaCroix AZ, Everett DF, Kovar MG. Aging in theeighties: the prevalence of co-morbidity and its association withdisability. Advance Data from Vital and Health Statistics, No. 170.Hyattsville, MD: National Center for Health Statistics, 1989.11. Guralnik JM. Understanding the relationship between disease anddisability. J Am Geriatr Soc 1994; 42: 1128–9.12. Stuck AE, Walthert JM, Nikolaus T et al. Risk factors for functionalstatus decline in community-living elderly people: a systematicliterature review. Soc Sci Med 1999; 48: 445–69.13. Branch LG, Meyers AR. Assessing physical function in the elderly.Clin Geriatr Med 1987; 3: 29–51.14. Applegate WB, Blass JP, Williams TF. Instruments for the functionalassessment of older patients. N Engl J Med 1990; 322: 1207–14.15. Guralnik JM, LaCroix AZ. Assessing physical function in olderpopulations. In Wallace RB, Woolson RF, eds, The Epidemiologic