Ageing or aging (see spelling differences) is the process of becoming older. The term refers especially to human beings, many animals, and fungi, whereas for example bacteria, perennial plants and some simple animals are potentially biologically immortal. In the broader sense, ageing can refer to single cells within an organism which have ceased dividing (cellular senescence) or to the population of a species (population ageing).
In humans, ageing represents the accumulation of changes in a human being over time, encompassing physical, psychological, and social changes. Reaction time, for example, may slow with age, while knowledge of world events and wisdom may expand. Ageing is among the greatest known risk factors for most human diseases: of the roughly 150,000 people who die each day across the globe, about two thirds die from age-related causes.
The causes of ageing are uncertain; current theories are assigned to the damage concept, whereby the accumulation of damage (such as DNA oxidation) may cause biological systems to fail, or to the programmed ageing concept, whereby internal processes (such as DNA methylation) may cause ageing. Programmed ageing should not be confused with programmed cell death (apoptosis).
Populations around the world are rapidly ageing. Ageing presents both challenges and opportunities. It will increase demand for primary health care and long-term care, require a larger and better trained workforce and intensify the need for environments to be made more age-friendly. Yet, these investments can enable the many contributions of older people – whether it be within their family, to their local community (e.g. as volunteers or within the formal or informal workforce) or to society more broadly.
Societies that adapt to this changing demographic and invest in Healthy Ageing can enable individuals to live both longer and healthier lives and for societies to reap the dividends.
Every person – in every country in the world – should have the opportunity to live a long and healthy life. Yet, the environments in which we live can favour health or be harmful to it. Environments are highly influential on our behaviour, our exposure to health risks (for example air pollution, violence), our access to quality health and social care and the opportunities that ageing brings.
Healthy Ageing is about creating the environments and opportunities that enable people to be and do what they value throughout their lives. Everybody can experience Healthy Ageing. Being free of disease or infirmity is not a requirement for Healthy Ageing as many older adults have one or more health conditions that, when well controlled, have little influence on their wellbeing.
Effects Of Ageing
Enlarged ears and noses of old humans are sometimes blamed on continual cartilage growth, but the cause is more probably gravity.
A number of characteristic ageing symptoms are experienced by a majority or by a significant proportion of humans during their lifetimes.
- Teenagers lose the young child’s ability to hear high-frequency sounds above 20 kHz.
- In the mid-20s, cognitive decline begins.
- Wrinkles develop mainly due to photoageing, particularly affecting sun-exposed areas (face).
- After peaking in the mid-20s, female fertility declines.
- After age 30 the mass of human body is decreased until 70 years and then shows damping oscillations.
- People over 35 years of age are at increasing risk for losing strength in the ciliary muscle, which leads to presbyopia and most people experience presbyopia, a difficulty focusing on close objects, by age 45–50. The cause is lens hardening by decreasing levels of α-crystallin, a process which may be sped up by higher temperatures.
- Around age 50, hair turns grey. Pattern hair loss by the age of 50 affects about 30–50% of males and a quarter of females.
- Menopause typically occurs between 49 and 52 years of age.
- In the 60–64 age cohort, the incidence of osteoarthritis rises to 53%. Only 20% however report disabling osteoarthritis at this age.
- Almost half of people older than 75 have hearing loss (presbycusis) inhibiting spoken communication. Many vertebrates such as fish, birds and amphibians do not suffer presbycusis in old age as they are able to regenerate their cochlearsensory cells, whereas mammals including humans have genetically lost this ability.
- By age 80, more than half of all Americans either have a cataract or have had cataract surgery.
- Frailty, defined as loss of muscle mass and mobility, affects 25% of those over 85.
- Atherosclerosis is classified as an ageing disease.It leads to cardiovascular disease (for example stroke and heart attack) which globally is the most common cause of death. Vessel aging causes vascular remodeling and loss of arterial elasticity and as a result causes the stiffness of the vasculature.
- Recent evidence suggests that age-related risk of death plateaus after age 105. The maximum human lifespan is suggested to be 115 years “for the foreseeable future”. The oldest reliably recorded human was Jeanne Calment who reportedly died in 1997 at 122, though recent research has disputed this.
Dementia becomes more common with age. About 3% of people between the ages of 65 and 74, 19% between 75 and 84, and nearly half of those over 85 years of age have dementia. The spectrum ranges from mild cognitive impairment to the neurodegenerative diseases of Alzheimer’s disease, cerebrovascular disease, Parkinson’s disease and Lou Gehrig’s disease. Furthermore, many types of memory decline with ageing, but not semantic memory or general knowledge such as vocabulary definitions, which typically increases or remains steady until late adulthood (see Ageing brain). Intelligence declines with age, though the rate varies depending on the type and may in fact remain steady throughout most of the lifespan, dropping suddenly only as people near the end of their lives. Individual variations in rate of cognitive decline may therefore be explained in terms of people having different lengths of life. There are changes to the brain: after 20 years of age there is a 10% reduction each decade in the total length of the brain’s myelinated axons.
Age can result in visual impairment, whereby non-verbal communication is reduced, which can lead to isolation and possible depression. Older adults, however, may not suffer depression as much as younger adults, and were paradoxically found to have improved mood despite declining physical health. Macular degeneration causes vision loss and increases with age, affecting nearly 12% of those above the age of 80. This degeneration is caused by systemic changes in the circulation of waste products and by growth of abnormal vessels around the retina.
A distinction can be made between “proximal ageing” (age-based effects that come about because of factors in the recent past) and “distal ageing” (age-based differences that can be traced to a cause in a person’s early life, such as childhood poliomyelitis).
Ageing is among the greatest known risk factors for most human diseases. Of the roughly 150,000 people who die each day across the globe, about two thirds—100,000 per day—die from age-related causes. In industrialized nations, the proportion is higher, reaching 90%
Prevention and delay
See also: Life extension
Caloric restriction substantially affects lifespan in many animals, including the ability to delay or prevent many age-related diseases. Typically, this involves caloric intake of 60–70% of what an ad libitum animal would consume, while still maintaining proper nutrient intake. No lifespan data exist for humans on a calorie-restricted diet, but several reports support protection from age-related diseases. Two major ongoing studies on rhesus monkeys initially revealed disparate results; while one study, by the University of Wisconsin, showed that caloric restriction does extend lifespan, the second study, by the National Institute on Aging (NIA), found no effects of caloric restriction on longevity. Both studies nevertheless showed improvement in a number of health parameters. Notwithstanding the similarly low calorie intake, the diet composition differed between the two studies (notably a high sucrose content in the Wisconsin study), and the monkeys have different origins (India, China), initially suggesting that genetics and dietary composition, not merely a decrease in calories, are factors in longevity. However, in a comparative analysis in 2014, the Wisconsin researchers found that the allegedly non-starved NIA control monkeys in fact are moderately underweight when compared with other monkey populations, and argued this was due to the NIA’s apportioned feeding protocol in contrast to Wisconsin’s truly unrestricted ad libitum feeding protocol. They conclude that moderate calorie restriction rather than extreme calorie restriction is sufficient to produce the observed health and longevity benefits in the studied rhesus monkeys.
Alternatively, the benefits of dietary restriction can also be found by changing the macro nutrient profile to reduce protein intake without any changes to calorie level, resulting in similar increases in longevity. Dietary protein restriction not only inhibits mTOR activity but also IGF-1, two mechanisms implicated in ageing.Specifically, reducing leucine intake is sufficient to inhibit mTOR activity, achievable through reducing animal food consumption.
The amount of sleep has an impact on mortality. People who live the longest report sleeping for six to seven hours each night. Lack of sleep (<5 hours) more than doubles the risk of death from cardiovascular disease, but too much sleep (>9 hours) is associated with a doubling of the risk of death, though not primarily from cardiovascular disease. Sleeping more than 7 to 8 hours per day has been consistently associated with increased mortality, though the cause is probably other factors such as depression and socioeconomic status, which would correlate statistically.
Physical exercise may increase life expectancy. People who participate in moderate to high levels of physical exercise have a lower mortality rate compared to individuals who are not physically active. Moderate levels of exercise have been correlated with preventing aging and improving quality of life by reducing inflammatory potential. The majority of the benefits from exercise are achieved with around 3500 metabolic equivalent (MET) minutes per week. For example, climbing stairs 10 minutes, vacuuming 15 minutes, gardening 20 minutes, running 20 minutes, and walking or bicycling for 25 minutes on a daily basis would together achieve about 3000 MET minutes a week.
Avoidance of chronic stress (as opposed to acute stress) is associated with a slower loss of telomeres in most but not all studies, and with decreased cortisol levels. A chronically high cortisol level compromises the immune system, causes cardiac damage/arterosclerosis and is associated with facial ageing, and the latter in turn is a marker for increased morbidity and mortality. A meta-analysis shows that loneliness carries a higher mortality risk than smoking. Stress can be countered by social connection, spirituality, and (for men more clearly than for women) married life, all of which are associated with longevity.
The following drugs and interventions have been shown to retard or reverse the biological effects of ageing in animal models, but none has yet been proven to do so in humans.
Evidence in both animals and humans suggests that resveratrol may be a caloric restriction mimetic.
Rapamycin was first shown to extend lifespan in eukaryotes in 2006 by Powers et al. who showed a dose-responsive effect of rapamycin on lifespan extension in yeast cells. In a 2009 study, the lifespans of mice fed rapamycin were increased between 28 and 38% from the beginning of treatment, or 9 to 14% in total increased maximum lifespan. Of particular note, the treatment began in mice aged 20 months, the equivalent of 60 human years. Rapamycin has subsequently been shown to extend mouse lifespan in several separate experiments, and is now being tested for this purpose in nonhuman primates (the marmoset monkey).
Cancer geneticist Ronald A. DePinho and his colleagues published research on mice where telomerase activity was first genetically removed. Then, after the mice had prematurely aged, they restored telomerase activity by reactivating the telomerase gene. As a result, the mice were rejuvenated: Shrivelled testes grew back to normal and the animals regained their fertility. Other organs, such as the spleen, liver, intestines and brain, recuperated from their degenerated state. “[The finding] offers the possibility that normal human ageing could be slowed by reawakening the enzyme in cells where it has stopped working” says Ronald DePinho. However, activating telomerase in humans could potentially encourage the growth of tumours.
Most known genetic interventions in C. elegans increase lifespan by 1.5 to 2.5-fold. As of 2009, the record for lifespan extension in C. elegans is a single-gene mutation which increases adult survival by tenfold. The strong conservation of some of the mechanisms of ageing discovered in model organisms imply that they may be useful in the enhancement of human survival. However, the benefits may not be proportional; longevity gains are typically greater in C. elegans than fruit flies, and greater in fruit flies than in mammals. One explanation for this is that mammals, being much longer-lived, already have many traits which promote lifespan
Healthy Ageing and functional ability
WHO defines Healthy Ageing “as the process of developing and maintaining the functional ability that enables wellbeing in older age”. Functional ability is about having the capabilities that enable all people to be and do what they have reason to value. This includes a person’s ability to:
- meet their basic needs;
- to learn, grow and make decisions;
- to be mobile;
- to build and maintain relationships; and
- to contribute to society.
Functional ability is made up of the intrinsic capacity of the individual, relevant environmental characteristics and the interaction between them.
Intrinsic capacity comprises all the mental and physical capacities that a person can draw on and includes their ability to walk, think, see, hear and remember. The level of intrinsic capacity is influenced by a number of factors such as the presence of diseases, injuries and age-related changes.
Environments include the home, community and broader society, and all the factors within them such as the built environment, people and their relationships, attitudes and values, health and social policies, the systems that support them and the services that they implement. Being able to live in environments that support and maintain your intrinsic capacity and functional ability is key to Healthy Ageing.
Key considerations of Healthy Ageing
Diversity: There is no typical older person. Some 80-year-olds have levels of physical and mental capacity that compare favourably with 30-year-olds. Others of the same age may require extensive care and support for basic activities like dressing and eating. Policy should be framed to improve the functional ability of all older people, whether they are robust, care dependent or in between.
Inequity: A large proportion (approximately 75%) of the diversity in capacity and circumstance observed in older age is the result of the cumulative impact of advantage and disadvantage across people’s lives. Importantly, the relationships we have with our environments are shaped by factors such as the family we were born into, our sex, our ethnicity, level of education and financial resources.
Healthy Ageing and Active Ageing
Healthy Ageing is the focus of WHO’s work on ageing between 2015 – 2030. Healthy Ageing replaces the World Health Organization’s previous Active ageing: a policy framework developed in 2002. Healthy Ageing, like Active Ageing, emphasizes the need for action across multiple sectors and enabling older people to remain a resource to their families, communities and economies.
Department of Ageing and Life-Course
World Health Organization