The only way to considerably increase human longevity in the future is to retard the aging process itself ( Olshansky et al., 1990 Butler et al., 2008). Because the increase in life expectancy was due to changes in the IMR independent of changes in aging rates is also the reason why the average lifespan of humans may be reaching a plateau. What happened last century was that the IMR, which is not affected by the aging rate, was lowered due to breakthroughs in different areas, such as in the war against infectious diseases, thus lowering mortality rates across the entire lifespan and increasing the life expectancy. Nonetheless, the rate of aging and the MRDT are thought to have remained unaltered for thousands of years ( Finch, 1990 Hayflick, 1994). In the US, it jumped from 47.3 years in 1900 to 77.3 years in 2002 ( CDC/NCHS, National Vital Statistics System, Mortality Data). For example, the life expectancy at birth increased considerably in the past 100 year. Changes in the MRDT are expected to reflect changes in the rate of aging, but the same is not true for the IMR ( Finch, 1990 Finch and Pike, 1996 de Magalhaes et al., 2005). This means that after our sexual peak, at roughly age 30, our chances of dying double approximately every 8 years.ĭemographic measurements of aging, such as the MRDT, may then serve as estimates of the rate of aging. In fact, human populations tend to have a MRDT around 8 years. Another important variable derived from the Gompertz equation is the mortality rate doubling time (MRDT) given by MRDT = 0.693/ G ( Finch, 1990, pp. From this equation-or even sometimes from the mortality plot-we can derive the initial mortality rate (IMR), which is the mortality rate independent of aging, often calculated from the mortality rate prior to its exponential increase with age in this case, IMR = 0.0002/year since that is the mortality rate at ages 10-20. From Figure 1 it is possible then to estimate the Gompertz equation by performing a simple regression analysis after maturity: m(t) = 8.84e 0.0800t with r 2 = 0.997. 111-113):īeing m(t) the mortality rate as a function of time or age ( t) A is the extrapolated constant to birth or maturity, and G is the exponential (Gompertz) mortality rate coefficient. The simplest, most widely used method is based on the Gompertz function ( Finch, 1990, pp. There are several mathematical functions that can be used ( Wilson, 1994 Strehler, 1999, pp. Mathematically, aging can be quantified from mortality curves such as that in Figure 1. Source: CDC/NCHS, National Vital Statistics System, Mortality Data. The black line represents the Gompertz function extrapolated from the mortality rates after maturity. 1).įigure 1: Mortality rates, expressed in deaths per 100,000 people, as a function of age for the 2002 US population. Indeed, one hallmark of aging in humans and in many other species is an age-related increase in mortality rates shortly after maturity (Fig. Demographic Measurements of AgingĪging has been defined as the collection of changes that render human beings progressively more likely to die ( Medawar, 1952). (Personally, I actually prefer the term "senescence." If this were an academic book, I would be tempted to use the term "senescence." Being a website with visitors from various backgrounds, I think the term "aging" is more accessible "senescence" now also frequently refers to cellular senescence.) Aging is one of the most complex biological processes, whose definition is intrinsically related to its phenotype, as developed below. Aging can simply refer to the passage of time and can even have a positive connotation as in "aging wine." In the context of, and unless otherwise noted, the term "aging" refers to the biological process of growing older in a deleterious sense, what some authors call "senescence" ( Williams, 1957 Comfort, 1964 Finch, 1990). Keywords: ageing, aging traits, biomarkers, demography, older peopleĪlthough everyone is familiar with aging, defining it is not so straightforward. Pathological and Physiological Age-Related Changes The different components of human aging are succinctly reviewed and several other key concepts in gerontology are defined. #Pathological aging how toHow to Help Fight Aging Immortality and Society Glossary Bibliography Links on Aging Who's Who in Gerontology Twitter Facebook
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