How individual age-associated changes may influence human morbidity and mortality patterns

Patterns of human mortality share common traits in different populations. T hey include higher mortality in early childhood. lower mortality during the reproductive period, all accelerated increase of mortality near the end of the reproductive period, and deceleration in the mortality increase at old est old ages. The deceleration of mortality rate is one of the most intrigu ing recent findings in longevity research. The role of differential selecti on in this phenomenon has been well studied. Possible contribution of indiv idual aging in the shape of mortality curve is also recognized. However, th is contribution has not been studied in details. In this paper, we specify most common patterns of age-associated changes in an individual organism an d discuss their possible influence on morbidity and mortality in Population . We subdivide individual age-associated changes into three components, hav ing different influence on morbidity and mortality: (1) basal, (2) ontogene tic, and (3) time-dependent. Basal changes are connected with the universal decrease in the rate of living during all individual life. As a result, so me phenotypic effects of aging may accumulate in an organism at a slower ra te with age. Basal changes are likely to contribute to a plateau of morbidi ty often observed at old ages, and may partially be responsible for mortali ty deceleration at oldest old ages. Ontogenetic component is connected with change of the stages of ontogenesis (e.g., the growth, the reproductive pe riod and the climacteric) during all individual life. The ontogenesis-relat ed changes contribute to wave-like patterns of morbidity in Population and may partially be responsible for mortality increase at middle ages and its deceleration at old ages. Time-dependent changes are connected with long-ti me exposure of all organism to different harmful factors. They are most lik ely to contribute to morbidity and mortality acceleration. We discuss how a ll three components of individual age-associated changes may interact in hu man organism and influence patterns of morbidity and mortality in populatio n. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.