What are the mechanisms of aging? The study of this fundamental question in gerontology is not limited to laboratory and clinical studies but is extended to demogaphic and epidemiological research, because age patterns of mortality and morbidity reflect some aspects of underlying mechanisms of progressive senescence. Recent studies using the life-table aging rate (LAR), defined as the rate of relative mortality increase with age, show distinct mathematical patterns of all-cause and cause-specific mortality in the first derivative of the logarithm of age-specific death rate. The clarity and regularity of the patterns suggest that they reflect some underlying processes. This project, therefore, will study relationships between aging and mortality through LAR patterns. The following questions are raised: 1. (All-cause mortality) A previous study on the mortality of old women shows that the LAR rises with age at younger old ages and declines with age at older old ages, resulting in a bell-shaped curve peaking around age 75. Why does the LAR follow such a trajectory? 2. (Cause-specific mortality) What age patterns does the LAR exhibit for each of the major causes of death? Do biomedical theories on relationships between aging and disease explain those cause-specific LAR patterns? 3. (Interrelationships) What mechanisms combine different LAR patterns of cause-specific mortality into the bell-shaped LAR curve of all-cause mortality? 4. (Trends) Are there any systematic trends in LAR patterns of all-cause and cause-specific mortality? If so, what explains the trends? 5. (Sex differentials) Are there any sex differentials in LAR patterns of all-cause and cause-specific mortality? If so, what explains the sex differentials? The central aim of this project is to investigate these problems by (a) analyzing internationally compiled data on death rates classified by age, sex and causes of death, (b) linking observed LAR patterns with biomedical theories on aging and disease, and (c) developing mathematical models on relationships between aging, disease and mortality based on results of (a) and (b).
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