A Condensed Overview of Aging: Life Expectancy, Risk, and Research
Increased life expectancy has led researchers to analyze the risks of aging and research its origins, preventions, and treatments.
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- As the human life span has recently extended, understanding aging has become essential to improving health and epidemiology. Research on aging analyzes life expectancy, risk, origins, and prevention.
The University of Cambridge states that life expectancy has nearly doubled. For example, the average life expectancy in the United Kingdom went from 40 to 80 years in the past 200 years.
Data from the CDC shows that by 2019 adults over 65 years old comprised approximately 16% of the population in the United States. Furthermore, the WHO estimates that by 2050 the global population of adults over 60 will reach 2.1 billion, doubling from 2020. Additionally, the number of adults over 80 years old will triple and reach 426 million.
According to a publication in EMBO Reports, “this dramatic rise happened mostly as a result of improved hygiene practices, success in averting epidemics and infectious diseases, and a sharp fall in infant mortality.”
Although aging has been studied and observed for decades, scientific researchers first began to study aging in the 1900s. It is universally understood that aging is associated with a greater risk of disease development and mental decline. As a result, many people actively search for ways to stop or slow down aging.
Reasons for trying to understand aging vary from aesthetic to philosophical, but clinical researchers who study aging predominantly focus on the molecular, biological explanations for an increased risk of disease development.
According to the National Institute of Aging (NIA), a subset of the NIH, “as scientists learn more about these processes, experiments can be designed to better understand when and how pathological changes begin, providing important clues toward developing interventions to prevent or treat disease.”
The Impact of Aging
Age is correlated with an increased risk of dementia, diabetes, heart disease, and other chronic illnesses.
Telomeres — the DNA sequences located at the ends of chromosomes — do not code for any genetic information. Instead, they function as a cap or protector for the part of the chromosome with genetic data. With all cell division, telomeres shorten, meaning that cells’ ability to protect genetic information decreases as they age.
The WHO states that “at the biological level, aging results from the impact of the accumulation of a wide variety of molecular and cellular damage over time. This leads to a gradual decrease in physical and mental capacity, a growing risk of disease and ultimately death.”
Historical Research on Aging
Understanding the history of aging across species may help inform further studies on the human lifespan.
According to Experimental Gerontology, the evolutionary theory contributed little to understanding aging. The journal states that this theory assumed that since animals in the wild died from predation or other extrinsic factors, there were few benefits forcing species to evolve alleles catered to old age.
The first indication of aging came when it was found that mortality curves across many different organisms were similar. Additionally, varying lifespans among and within species indicate the science behind aging.
Caloric Restriction
A 2021 article in the Journal of Gerontology separates aging research into eras, one of the first being the era of caloric restriction. Due to studies on rats and mice, it was theorized that caloric restriction would slow down aging.
After studies on calorie restriction (CR) were presented, the first real case behind aging developed. Research in an Experimental Gerontology review states, “CR is simplicity at its best: by reducing food intake by a specific amount (in mice, this equates to 30–40% below ad libitum), one can extend the average and maximum lifespan of a wide variety of organisms.”
According to a 2019 review published in Nature, the first step in aging research occurred in 1939 when a study of reducing the caloric intake in mice was found to increase their life spans.
“During the 1970s and 1980s, research led by Edward Masoro at the University of Texas Health Science Center with rats and Roy Walford at the University of California at Los Angeles with mice demonstrated conclusively to the research community that CR had a major impact on aging. For example, it prevented/delayed the incidence of most age-related diseases and pathologies in rodents and improved a wide variety of physiological processes that declined with age,” stated writers in the Journal of Gerontology.
Many additional studies were done on the effect of caloric restriction on aging, which determined that the results applied to rodents and primates.
Later, the CALERIE (Comprehensive Assessment of Long-term Effects of Reducing Intake of Energy) study, which the NIA started in 2001, found similar results among humans.
“The study demonstrated the feasibility of sustained human CR (for two years) and showed improvement of predictors of longevity and cardiometabolic risk factors. Thus, the effect of CR on aging appears to translate from rodents to humans, demonstrating the usefulness of rodents in studying interventions of aging,” stated the researchers in the publication.
Genetics and Aging
It is widely understood that lifespan can be hereditary, implying that aging has a genetic basis. Peter Medawar’s 1952 claim that “aging is the result of the decline in the force of natural selection after reproduction” informed further studies on the genetics of aging.
It wasn’t until 1988 that a study on nematodes led to the discovery of the age-1 gene, which impacts lifespan. Mutations in the age-1 gene of nematodes led to a 40–60% increase in lifespan. Since then, multiple other genes associated with aging have been discovered.
“The genetics of aging research has revealed a complex network of interacting intracellular signaling pathways and higher-order processes. Many of the pathways and processes, such as dietary restriction, that have been identified are known to be critical in homeostatic responses to environmental change,” stated researchers in the publication.
Telomeres and Aging
The NIA suggests that “there is enormous interest in the potential uses of cloning, gene therapy, and adult stem cell transplantation, as well as tissue transplantation, to combat diseases of aging.”
Recent studies in cattle have shown that implanting adult cattle fibroblasts into an egg yielded a healthy calf with normal length telomeres rather than shorter telomeres. This implies that gestation resets telomere length. Despite this research, it is unclear what long-term effects this implantation will have.
Cell Transplantation and Aging
There is an additional sector of aging research that focuses on cell transplantation. The NIA states, “recent research has shown that isolated cow or human adrenal gland cells inserted into immunodeficient mice formed functional adrenal tissue that resembles a normal adrenal gland.”
The implications of this research suggest a wide range of uses for regenerative therapy to address issues and illnesses associated with aging.
Oxidative Stress
Aging research also emphasizes understanding lifespan and focuses on how to extend it.
According to the NIA, “it is widely accepted that oxidative stress is a factor in aging,” although there have been no natural antioxidants proven to have a significant impact on aging to date.
However, some research has suggested that EUK-134 — an artificial enzyme that functions similarly to superoxide dismutase and catalase, which reduce oxidative damage — may help reduce oxidative damage.
Further Research on Aging
It is important to note that many people believe that age causes age-related diseases. However, while there is a correlation between the two, causality has yet to be proven with current data.
Because previous research only scrapes the surface of aging, additional research funding is needed to continue exploring the physiological pathways of aging.
Based on data from the NIH, an estimated $6,069 million will be spent on aging research in 2022, an increase of approximately $412 million more than the 2021 spending budget.
Further research to establish the link between aging and disease risk and determine how extended lifespans could lead to healthier elderly populations and reduce the burden of age-related chronic illnesses.
