Thelast phase of the lifespan includes death and dying. Most other developments across the rest of the lifespan represent sets of options, but this last step is not optional. It is where all our earthly journeys end. In this chapter, we explain differences in life expectancy and the factors that influence length of life, as well as theories of aging itself. We consider the end of life and how it is approached in different cultures. We examine the ways that conceptions of death differ and develop across childhood and adolescence, as well as processes of grief and bereavement and the factors that influence how they unfold and are resolved.
Lifespan or maximum lifespan refer to the greatest age reached by any member of a given species (or population). For humans, the lifespan is currently between 120 and 125. Life expectancy is defined as the average number of years that members of a species (or population) live. According to the World Health Organization (WHO) (2019) global life expectancy for those born in 2019 is 72.0 years, with females reaching 74.2 years and males reaching 69.8 years. Women live longer than men around the world, and the gap between the sexes has remained the same since 1990. Overall life expectancy ranges from 61.2 years in the WHO African Region to 77.5 years in the WHO European Region. Global life expectancy increased by 5.5 years between 2000 and 2016. Improvements in child survival and access to antiretroviral medication for the treatment of HIV are considered the main reasons for this increase. However, life expectancy in low-income countries (62.7 years) is 18.1 years lower than in high-income countries (80.8 years). In high-income countries, the majority of people who die are old, while in low-income countries almost one in three deaths are in children under 5 years of age. According to the Central Intelligence Agency (2019) the United States ranks 45th in the world for life expectancy.
World Healthy Life Expectancy. A better way to appreciate the diversity of people in late adulthood is to go beyond chronological age and examine how well the person is aging. Many in late adulthood enjoy better than average health and social well-being and so are aging at an optimal level. In contrast, others experience poor health and dependence to a greater extent than would be considered typical. When looking at large populations, the WHO (2019) measures how many equivalent years of full health on average a newborn baby is expected to have. This age, called The Healthy Life Expectancy, takes into account current age-specific mortality, morbidity, and disability risks. In 2016, the global Healthy Life Expectancy was 63.3 years up from 58.5 years in 2000. The WHO African Region had the lowest Healthy Life Expectancy at 53.8 years, while the WHO Western Pacific Region had the highest at 68.9 years.
American Healthy Life Expectancy. To determine the current United States Healthy Life Expectancy (HLE), factors were evaluated in 2007-2009 to determine how long an individual currently at age 65 will continue to experience good health (CDC, 2013). The highest Healthy Life Expectancy (HLE) was observed in Hawaii with 16.2 years of additional good health, and the lowest was in Mississippi with only 10.8 years of additional good health. Overall, the lowest HLE was among southern states. Females had a greater HLE than males at age 65 years in every state and DC. HLE was greater for whites than for blacks in DC and all states from which data were available, except in Nevada and New Mexico.
The people inhabiting blue zones share common lifestyle characteristics that contribute to their longevity. The Venn diagram below (Figure 10.19) highlights the following six shared characteristics among the people of Okinawa, Sardinia, and Loma Linda blue zones. Though not a lifestyle choice, they also live as isolated populations with a related gene pool.
Men are more likely to contract viral and bacterial infections, and their immunity at the cellular level decreases significantly faster with age. Although women are slightly more prone to autoimmune and inflammatory diseases, such as rheumatoid arthritis, the gradual deterioration of the immune system is slower in women (Caruso, Accardi, Virruso, & Candore, 2013; Hirokawa et al., 2013).
Looking at the influence of hormones, estrogen levels in women appear to have a protective effect on their heart and circulatory systems (Via, Borrs, Gambini, Sastre, & Pallard, 2005). Estrogens also have antioxidant properties that protect against harmful effects of free radicals, which damage cell components, cause mutations, and are in part responsible for the aging process. Testosterone levels are higher in men than in women and are related to more frequent cardiovascular and immune disorders. The level of testosterone is also responsible, in part, for male behavioral patterns, including increased level of aggression and violence (Martin, Poon, & Hagberg, 2011; Borysławski & Chmielewski, 2012).
Lifestyle Factors. Certainly not all the reasons women live longer than men are biological. As previously mentioned, male behavioral patterns and lifestyle play a significant role in the shorter lifespans for males. One significant factor is that males work in more dangerous jobs, including police, fire fighters, and construction, and they are more exposed to violence. According to the Federal Bureau of Investigation (2014) there were 11,961 homicides in the U.S. in 2014 (last year for full data) and of those 77% were males. Further, males serve in the military in much larger numbers than females. According to the Department of Defense (2015), in 2014 83% of all officers in the Services (Navy, Army, Marine Corps and Air Force) were male, while 85% of all enlisted service members were male. Males are also more than three times as likely to commit suicide (CDC, 2016a).
Genetics. Genetic make-up certainly plays a role in longevity, but scientists are still attempting to identify which genes are responsible. Based on animal models, some genes promote longer life, while other genes limit longevity.
Specifically, longevity may be due to genes that better equip someone to survive a disease. For others, some genes may accelerate the rate of aging, while others slow that rate. To help determine which genes promote longevity and how they operate, researchers scan the entire genome and compare genetic variants in those who live longer with those who have an average or shorter lifespan. For example, a National Institutes of Health study identified genes possibly associated with blood fat levels and cholesterol, both risk factors for coronary disease and early death (NIA, 2011a). Researchers believe that it is most likely a combination of many genes that affect the rate of aging.
Cellular Clock Theory. This theory suggests that biological aging is due to the fact that normal cells cannot divide indefinitely. This is known as the Hayflick limit, and is evidenced in cells studied in test tubes, which divide about 40-60 times before they stop (Bartlett, 2014). But what is the mechanism behind this cellular senescence? At the end of each chromosomal strand is a sequence of DNA that does not code for any particular protein, but protects the rest of the chromosome, which is called a telomere.
With each replication, the telomere gets shorter. Once it becomes too short the cell does one of three things. It can stop replicating by turning itself off, called cellular senescence. It can stop replicating by dying, called apoptosis. Or, as in the development of cancer, it can continue to divide and become abnormal. Senescent cells can also create problems. While they may be turned off, they are not dead, thus they still interact with other cells in the body and can lead to an increase risk of disease. When we are young, senescent cells may reduce our risk of serious diseases such as cancer, but as we age they increase our risk of such problems (NIA, 2011a). The question of why cellular senescence changes from being beneficial to being detrimental is still under investigation. The answer may lead to some important clues about the aging process.
Mitochondrial Damage. Damage to mitochondrial DNA can lead to a decaying of the mitochondria, which is a cell organelle that uses oxygen to produce energy from food. The mitochondria convert oxygen to adenosine triphosphate (ATP) which provides the energy for the cell. When damaged, mitochondria become less efficient and generate less energy for the cell and can lead to cellular death (NIA, 2011a).
Free Radicals. When the mitochondria use oxygen to produce energy, they also produce potentially harmful byproducts called oxygen free radicals (NIA, 2011a). The free radicals are missing an electron and create instability in surrounding molecules by taking electrons from them. There is a snowball effect (A takes from B and then B takes from C, etc.) that creates more free radicals which disrupt the cell and causes it to behave abnormally (See Figure 10.22). Some free radicals are helpful as they can destroy bacteria and other harmful organisms, but for the most part they cause damage in our cells and tissue. Free radicals are identified with disorders seen in those of advanced age, including cancer, atherosclerosis, cataracts, and neurodegeneration. Some research has suggested that adding antioxidants to our diets can help counter the effects of free radical damage because the antioxidants can donate an electron that can neutralize damaged molecules. However, the research on the effectiveness of antioxidants is not conclusive (Harvard School of Public Health, 2016).
Immune and Hormonal Stress Theories. Ever notice how quickly U.S. presidents seem to age? Before and after photos reveal how stress can play a role in the aging process. When gerontologists study stress, they are not just considering major life events, such as unemployment, death of a loved one, or the birth of a child. They are also including metabolic stress, the life sustaining activities of the body, such as circulating the blood, eliminating waste, controlling body temperature, and neuronal firing in the brain. In other words, all the activities that keep the body alive also create biological stress.
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