Date of release: 14 August, 2017
Longevity in women and reproductive factors?
Introduction
In this aging world, the field of the 'epidemiology of longevity' has been expanding rapidly in recent years. With a dramatic increase in survival rate to advanced old age over the past century, longevity can be described as an epidemic. Many studies have evaluated the impact of factors such as low socioeconomics in childhood, genetics, environmental, dietary and lifestyle (smoking and alcohol use), which negatively affect longevity. Although mortality rates for females are lower at each age than those of men, a close association between reproductive characteristics and longevity was recently documented.
Comment
The age of 85 years is often used to define the oldest old but there is no single accepted age threshold for longevity. Persons achieving an age of 90 or more years remain overwhelmingly White, at 88.1%, with African Americans making up 7.6% and Asians 2.2% of the over-90 population. Several long-term cohort studies have followed older adults long enough to identify the most long-lived and to define many factors that lead to a long lifespan [7]. Female life expectancy is increasing globally in this century, by more than 25-30 years in developed countries, and women live longer than men, on average [8].
Currently, a female life expectancy advantage is nearly universal, except in some southern Asian and sub-Saharan African societies where cultural factors (low female social status and stronger preference for male offspring) predominate. Women have better survival at every age and thus appear to be more robust, rather than aging more slowly [9]. This assumption is justified as human reproductive senescence occurs much faster than somatic aging and females exhibit prolonged post-reproductive lifespans (PRLSs). Determining the factors that influence and mechanisms that underpin PRLSs has proved a significant challenge. Many classic and modern hypotheses propose to explain PRLSs and discuss their application in humans [10]. The disposable soma theory of aging argues that investment in reproduction deprives organisms of resources required for self-maintenance, thus reducing longevity. This effect might be more easily explained in females of developing countries, through the direct physical burdens of pregnancy, childbirth and breastfeeding. The Reproductive Cell Theory of Aging maintains that hormones which promote growth and development early in life, to achieve reproductive maturity, act later in an antagonistic pleiotropic manner, promoting senescence. A genetic predisposition to hinder and/or delay these hormonal mechanisms might reduce reproductive success and at the same time delay aging and mortality in women and men alike [11-13]. It is important to note that there is already robust evidence that reproductive events are associated with women's longevity; however, reproductive longevity has not increased over the same period of time. The association of age at childbirth with all-cause mortality has been inconsistent. Data on a woman's childbearing history and her later health and mortality correlation indicate that, on reaching midlife and controlling for early and later socioeconomic status, first birth before age 20 is associated with a hazard of early death [14]. In conclusion, current efforts to find clear information on the association of reproductive characteristics with late-age survival/life expectancy can help to identify targets for future public health interventions in the area of pre-conception and family planning counselling, thereby improving their healthy longevity in the long term. However, future studies to identify genetic factors in reproductive fitness, rate of aging and age-related conditions are advocated for deeper understanding of underlying biological pathways. There is a clear need for more prospective studies with large numbers of exceptional survivors to determine the relationship between age at childbirth and survival to extreme old age. There is much work to be undertaken in this area.Comentario
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