Frank Steven A
Department of Ecology and Evolutionary Biology, University of California, Irvine, CA 92697-2525 USA.
BMC Biol. 2004 Jul 8;2:16. doi: 10.1186/1741-7007-2-16.
Humans die at an increasing rate until late in life, when mortality rates level off. The causes of the late-life mortality plateau have been debated extensively over the past few years. Here, I examine mortality patterns separately for each of the leading causes of death. The different causes of death show distinct mortality patterns, providing some clues about the varying acceleration of mortality at different ages.
I examine mortality patterns by first plotting the data of mortality rate versus age on a log-log scale. The slope of the age-specific mortality rate at each age is the age-specific acceleration of mortality. About one-half of total deaths have causes with similar shapes for the age-specific acceleration of mortality: a steady rise in acceleration from midlife until a well-defined peak at 80 years, followed by a nearly linear decline in acceleration. This first group of causes includes heart disease, cerebrovascular disease, and accidental deaths. A second group, accounting for about one-third of all deaths, follows a different pattern of age-specific acceleration. These diseases show an approximately linear rise in acceleration to a peak at 35-45 years of age, followed by a steep and steady decline in acceleration for the remainder of life. This second group includes cancer, chronic respiratory diseases, and liver disease. I develop a multistage model of disease progression to explain the observed patterns of mortality acceleration.
A multistage model of disease progression can explain both the early-life increase and late-life decrease in mortality acceleration. An early-life rise in acceleration may be caused by increasing rates of transition between stages as individuals grow older. The late-life decline in acceleration may be caused by progression through earlier stages, leaving only a few stages remaining for older individuals.
人类死亡率不断上升，直至晚年才趋于平稳。在过去几年里，人们对晚年死亡率平稳期的成因进行了广泛辩论。在此，我分别研究了每种主要死因的死亡率模式。不同的死因呈现出不同的死亡率模式，这为不同年龄阶段死亡率加速变化的差异提供了一些线索。
我首先通过在对数-对数尺度上绘制死亡率与年龄的数据来研究死亡率模式。每个年龄的年龄特异性死亡率斜率就是死亡率的年龄特异性加速度。大约一半的总死亡病例的死因，其年龄特异性死亡率加速度具有相似的形状：从中年期开始加速度稳步上升，直至80岁时达到明确的峰值，随后加速度几乎呈线性下降。第一组死因包括心脏病、脑血管疾病和意外死亡。第二组死因约占所有死亡病例的三分之一，其年龄特异性加速度遵循不同的模式。这些疾病的加速度在35 - 45岁时近似线性上升至峰值，随后在余生中加速度急剧且稳定地下降。第二组死因包括癌症、慢性呼吸道疾病和肝病。我建立了一个疾病进展的多阶段模型来解释观察到的死亡率加速模式。
一个疾病进展的多阶段模型可以解释死亡率加速度在生命早期的上升和晚期的下降。生命早期加速度的上升可能是由于个体随着年龄增长阶段转换率增加所致。生命晚期加速度的下降可能是由于在早期阶段的进展，导致老年个体只剩下少数几个阶段。
