May 02, 2012

Expected gain in Life Expectancy by Curing diseases

An integrated approach to cause-of-death analysis: cause-deleted life tables and decompositions of life expectancy

This article integrates two methods that analyze the implications of various causes of death for life expectancy. One of the methods attributes changes in life expectancy to various causes of death; the other method examines the effect of removing deaths from a particular cause on life expectancy. This integration is accomplished by new formulas that make clearer the interactions among causes of death in determining life expectancy. We apply our approach to changes in life expectancy in the United States between 1970 and 2000. We demonstrate, and explain analytically, the paradox that cancer is responsible for more years of life lost in 2000 than in 1970 despite the fact that declines in cancer mortality contributed to advances in life expectancy between 1970 and 2000.

                                        1970      2000
Heart                                 6.20      3.93 
Malignant neoplasms                     2.54      3.27
Cerebrovascular                         1.26      0.70
Violence                                1.86      1.20
Chronic lower respiratory diseases 0.20      0.55
Diabetes                                0.25      0.34
Influenza and pneumonia                 0.50      0.25
Nephritis, nephrotic syndrome,nephrosis 0.07      0.16
Septicemia                              0.03      0.14
Chronic liver disease and cirrhosis 0.29      0.17
Hypertension, hypertensive renal        0.05      0.07
All other                               3.21      2.99

The methodology produces more of a relative guide to the impact of a disease. It is not likely to be correct as a prediction in how much life expectancy would be gained.

The impact of deaths assigned to a particular cause on life table values can be gauged by recalculating the life table without deaths assigned to that cause. The results provide an estimate of how the intensity and age-distribution of deaths assigned to a particular cause affect all life table values, including life expectancy. To function as an epidemiologic prediction, one would have to assume that all deaths from a particular cause were eliminable, which is rarely possible, and that death rates from other causes would not be changed by the elimination. Such an assumption may be tenable as a first approximation for broad causes of death categories such as infectious diseases, violence, cardiovascular disease, and cancer, but it is clearly not tenable for disease processes such as diabetes that manifest themselves in many different causes of death.

After several decades of slow improvement in mortality, the United States experienced substantial advances in longevity between 1970 and 2000. These are widely believed to reflect primarily reductions in death rates from cardiovascular diseases, facilitated by medical advances such as cardiovascular bypass surgery and expanded use of blood pressure reduction drugs, statins, and beta blockers, as well as by reductions in cigarette smoking.

The estimated life expectancy at birth for the total U.S. population in 1970 to be 70.70 years (slightly lower than the value of 70.9 estimated by the NCHS (1974)) and 76.96 years for the year 2000 (slightly higher than the value of 76.9 estimated by Arias (2002)). Thus, life expectancy at birth is estimated to have increased by about 6.26 years between 1970 and 2000 for the total population of the U.S.

Note: there has not been a cure for all of those diseases and yet the life expectancy of Manoco is currently 89.7 years. This would be equal to the year 2000 US life expectancy with the adjustment of a cure for all diseases.

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