Compression of morbidity 1980-2011: a focused review of paradigms and progress

Abstract

The Compression of Morbidity hypothesis-positing that the age of onset of chronic illness may be postponed more than the age at death and squeezing most of the morbidity in life into a shorter period with less lifetime disability-was introduced by our group in 1980. This paper is focused upon the evolution of the concept, the controversies and responses, the supportive multidisciplinary science, and the evolving lines of evidence that establish proof of concept. We summarize data from 20-year prospective longitudinal studies of lifestyle progression of disability, national population studies of trends in disability, and randomized controlled trials of risk factor reduction with life-style-based "healthy aging" interventions. From the perspective of this influential and broadly cited paradigm, we review its current history, the development of a theoretical structure for healthy aging, and the challenges to develop coherent health policies directed at reduction in morbidity.

Figure 1

Scenarios for future morbidity. The three major population scenarios in the upper part of the figure represent (1) depiction of a present health, (2) a future where both life expectancy and morbidity are both increased, and (3) a future where both the time period after first morbidity and the amount of morbidity are decreased, resulting in Compression of Morbidity. Shaded areas represent under the curve cumulative morbidity. In the Compression of Morbidity scenario, lifetime disability is decreased. National disability trends over time are the algebraic sum of the eight individual trajectories illustrated at the bottom of the figure and many more. Some individual scenarios may add morbidity to a population average and some may subtract from it. The area under the morbidity curve is a useful metric for population health or health-related quality-of-life. The variables that affect the area under the curve are many and complex and have not yet been well delineated (see text).

Figure 2

US expected age at death from birth and from age 65, 1950–2007. The lower line shows life expectancy from birth, rising 9.7 years over this period. The upper line takes life expectancy from age 65 and adds 65 years to represent the expected age at death for those who have already survived to age 65; it rises 4.7 years over this period. The lines, while convergent, cannot actually meet unless there are no deaths before age 65. The lines cannot cross; hence the theoretical point of convergent is sometimes termed the “Point of Paradox”.

Figure 3

Development of disability with age in seniors after age 68 subjects with low (0), moderate (1) and high (2-3) risk factors in 1986. The University of Pennsylvania Study, over 21 years, has followed seniors from age 68 in three strata: Low Risk, with no baseline risk factors of smoking, obesity, or lack of exercise; Moderate Risk, where one risk factor was present at baseline, and High Risk, where two or three risk factors were present at baseline. The lower line represents low risk subjects, the middle line moderate risk subjects, and the top line high risk subjects. Differences are major whether looked at by vertical differences, or by longitudinal ones (postponement). When contrasted with mortality rates, Compression of Morbidity by health risk factor status is demonstrated across these groups.

Figure 4

Cumulative disability in seniors by risk groups. Lifetime disability is estimated by summing disability reported from each year for each subject, then averaging by risk group. Results are consistent across men, women, all subjects, survivors, decedents, those with no disability at baseline, and other subgroups at baseline. Greater numbers of risk factors are consistently associated with much more cumulative lifetime disability, a surrogate metric for Compression of Morbidity.

Figure 5

Disability progression—ages 58–79 years: Runners' Club and Community Controls. Progression of disability in Runner's Club and Community Control groups over 21 years from an average age of 58 is compared in the figure both with yearly disability values and statistically derived regression lines. The regression lines are derived from linear mixed models and adjusted for age, gender, BMI, smoking, and initial disability. Comparison of postponement of disability is represented by the absolute difference between the two groups in the time required to develop a given level of disability. The example shown is to reach Health Assessment Questionnaire (HAQ) Disability Index Scores of 0.10, 0.15, and 0.20. All differences are highly statistically different (P < 0.001). Lines continue to diverge with age. The postponement is 8.6 years between groups in reaching the  .010 mark, 12.6 years to reach the 0.15 mark, and projected at 16.6 years for the HAQ level of 0.20. Consistent moderately active exercise postpones onset of disability for many years.