Normal aging

Normal agingThe evolution of society in the twentieth century has been strongly marked by the considerable increase in the life expectancy of the population. The increase in the number of elderly people is very directly related to health professionals, because of the very high prevalence of chronic diseases in this part of the population. During the second half of the twentieth century, two new disciplines devoted specifically to the study of aging and the elderly were built, geriatrics and gerontology.

Although the word aging is part of everyday language, its definition and the notions it supports are less simple than they seem. It is important to distinguish between the aging of organisms or individuals and the aging of the population, which are two very different concepts.



From a biological point of view, aging or senescence can be defined as a physiological, slow and progressive process that modifies living organisms over time, starting from their maturity phase. It is a natural and obligatory process that concerns all individuals, and it is distinct from diseases that affect only some of them.

Longevity is another important concept in the study of aging. This is the maximum duration of life observed in a given species. It varies greatly from one species to another (a few days for Drosophila, 2-3 years for rats, a few decades for most primates, 120 years for humans, 200-300 years for turtles). Some terms related to the study of aging are presented and defined in the box.

Study methods:

The biology of aging has two main fields of study: the effects and mechanisms of aging on the one hand, and longevity on the other. The relationship between longevity and aging processes is probably more complex than it seems and remains unclear today. The methods of studies in the biology of aging are numerous: studies of the in vitro aging of cells; animal or human studies in vivo; transversal experimental designs (study at a given moment of individuals of different ages) or longitudinal studies (study of changes over time in a group of individuals); study of centenarians as an example of extreme aging.

Among the experimental animals frequently used in the biology of aging, mention must be made of Drosophila, mice and rats, 
and a worm, Caenorhabditis elegans, whose genome has been completely sequenced.

Mechanisms causing aging:

The mechanisms that cause aging are not well known. They are certainly multiple and complex, and their respective roles may vary according to the organs studied and also species. In the past, dozens of theories have been developed to explain the mechanism of aging, but most of them do not withstand the test of experimental studies.

1. Genetic factors:

They are certainly major. The differences in longevity between species are a first illustration. Above all, experimental modifications of certain genes have made it possible to dramatically modify the longevity of certain experimental animals (C. elegans, Drosophila, mouse). Werner syndrome and progeria, two childhood diseases responsible for premature aging, are each determined by the mutation of a single gene. Changes in genetic material acquired over the course of life may also be involved in the mechanisms of aging.

At each cell division, the telomeres (DNA fragments) located at the end of the chromosomes undergo deletions which lead, when they reach a certain importance, to alter their regulatory functions of the expression of the genes of this chromosome. Telomeres would thus be the substratum of the biological clock.

In addition, other acquired modifications of the genetic material could also intervene (exposure to natural radioactivity, exposure to solar radiation for the skin).

2. Metabolic factors:

Metabolic factors play an important role during aging. Non-enzymatic protein glycation is involved in the aging of tissues rich in connective tissue, such as the skin and the cardiovascular system. The interaction between sugars (glucose, pentose) and NH radicals of long half-life proteins (collagen, elastin) leads to a series of chemical reactions (Maillard reaction) to the formation of advanced glycation products and to bridges between the collagen fibers.

These reactions explain the increase in rigidity of the vessels, the main characteristic of arterial aging. Indeed, the administration of substances that inhibit the glycation of proteins prevents the stiffening of the arteries during aging, and substances capable of cleaving collagen bypasses restore their flexibility to the arteries of elderly individuals.

Free radicals produced during oxygen metabolism are involved in the aging process. In the mitochondria, reactive species of oxygen or free radicals escape from the chain of cellular respiration. These substances have a high chemical reactivity and can interact and alter molecules vital for cells (membrane lipids, DNA, RNA, in particular). The cells have mechanisms capable of capturing / inactivating these free radicals before they cause lesions: enzymes (superoxide dismutase, glutathione peroxidase, catalase) or antioxidant substances (vitamin E). During aging, these systems become less efficient, so that the toxicity of free radicals would be increased. The transfer and overexpression of genes encoding antioxidant enzymes has been shown to increase the longevity of some experimental animals and to delay some effects of their aging.

3. Hormonal factors:

Several hormonal systems have been implicated in aging mechanisms. The difference in longevity between men and women has led to the suspicion of the role of estrogen on the aging process, especially since in menopausal women is a major hormonal event that modifies the functioning of the body and accelerates certain effects of the body. aging (bone loss, skin changes). The potential of estrogen to slow down the aging of women has been severely undermined by the overall negative results of controlled studies of menopausal hormone therapy.

Growth hormone (GH), whose secretion decreases in the elderly, has also been implicated in the mechanism of aging.It could intervene by reducing the production of IGF-1 and thus reduce the synthesis of proteins in the body. The administration of GH makes it possible to oppose certain effects of aging (loss of muscle mass, decrease in skin thickness). Its application in humans is not wise because its effects are modest and the serious adverse effects are real.

The role of insulin during aging has been mentioned.

It is observed during aging insulin resistance that can promote cardiovascular aging, particularly through post-prandial hyperglycemia accelerating glycation phenomena.

Dehydroepiandrosterone (DHEA) is an adrenal androgen whose secretion decreases during aging.

This hormone does not seem to have a direct effect but is a precursor for other steroid hormones such as testosterone.

The administration of DHEA to healthy elderly people had no significant effect in men and modest effects in women.

4. Physical inactivity / physical activity, diet and other factors:

Other factors have been described as potentially involved during aging. The role of sedentary / physical activity emerges very clearly from the research.

The sedentary lifestyle is accompanied by a more pronounced aging on the cardiovascular and muscular system.Conversely, regular physical activity over the course of life is associated with less pronounced aging at the cardiovascular and muscular levels.

Numerous experimental studies have shown that a caloric restriction applied from maturity results in a slowing down of certain effects of aging and an increase in longevity. The implication for the man of this research is very uncertain, and some authors consider that these protocols of caloric restriction correspond rather to the correction of the habitual overeating of the animals of experiment (food at will), of more deprived of activity. physical.

Many other factors that may occur during aging have been discussed. Their role is less well documented by scientific work.



In general, aging causes a decrease in the functional capacities of the body. It should also be noted that the functional impact of aging is highly variable from one individual to another (high interindividual variability). Moreover, the importance of this repercussion is not homogeneous in the organism, the functions of certain organs being able to deteriorate more than others in the same individual. Also, the effects of aging in particular individuals are sometimes far removed from average aging (described from group observations).

The decrease in functional capacities related to aging mainly concerns the reserve capacities that are mobilized in situations where the needs of the body (effort, stress, aggression) increase. Also, the functional consequences of aging are more apparent in these situations than in the conditions of life at rest and protected.

Vulnerability results from the situation where the decline in reserve capacity is such that the organization can no longer cope with a moderate or even low increase in needs.

Effects on body composition and metabolism

If the average weight is slightly modified during aging, the fat mass is increased and the lean mass decreased.

At the metabolic level, insulin resistance is observed and the rest energy expenditure is slightly decreased. At equal physical activity, daily energy needs are very close to those of younger adults.

Neurological and sensory effects:

The motor and sensory functions of the brain as well as the control of the tone are not modified. Synaptic transmission is slowed, but this is not noticeable in activities of daily living.

The sleep is very modified: decrease of the duration of the sleep, fragmentation, but especially qualitative modification of the organization of the sleep.

The feeling of thirst is blunted: in the elderly, a greater increase in plasma osmolality is needed to induce thirst than in younger adults.

Circadian biological rhythms are less well regulated in the elderly, and the secretion of melatonin is decreased.

In peripheral nerves, there is an increase in nerve conduction time and a decrease in proprioceptive sensitivity.

The effects of aging on the autonomic nervous system are characterized by an increase in sympathetic nerve activity and catecholamine secretion, which contrast with a decrease in sympathetic responses due to decreased sensitivity of beta-adrenergic receptors.

The effectiveness of the regulation of body temperature decreases due to neurological and vascular factors.

Many sensory functions are very affected by aging.

The hearing loss associated with aging or presbycusis initially relates to the perception of high-pitched sounds. The vision is concerned by two phenomena: the presbyopia corresponds to a diminution of the capacities of accommodation; cataract is a gradual opacification of the lens causing a decrease in visual acuity. The effects of aging on smell and olfaction are less well documented.

Effects on the musculoskeletal system:

The muscle mass decreases during aging (sarcopenia) with mainly a decrease in the density of type II muscle fibers.The muscular strength decreases and the maximum effort capacity evaluated by the VO2 max decreases with age.The aging of the cartilage is characterized by a decrease in its water content and the number of chondrocytes and by modifications of its glycosaminoglycans. The cartilage is thinned and its mechanical properties are altered. The bone density and its mechanical resistance decrease during aging.

These processes are accelerated in women during the menopausal period.

Effects on cardiovascular and respiratory systems:

Aging leads to a gradual increase in the rigidity of the arteries. The blood pressure and blood flow damping function, which is closely related to the compliance of large vessels, is less effective in elderly patients, resulting in an increase in systolic blood pressure and pulse pressure. The increase in the afterload is associated with an increase in the cardiac mass. At the cardiac level, aging causes a decrease in the compliance of the left ventricle and a decrease in ventricular filling at the beginning of diastole. On the other hand, the filling of the left ventricle at the end of diastole is increased because of the compensatory increase of the atrial contraction. The ability of the heart to increase its heart rate in response to stimulation of the sympathetic nervous system decreases during aging. As the heart ages, the heart operates at higher pressure regimes, but finally the cardiac output at rest and effort is maintained.

Pulmonary aging is characterized by a decrease in ventilatory capacity, pulmonary and thoracic compliances and oxygen permeability at the level of the alveolocapillary membrane, leading to a decrease in the O2 partial pressure of the arterial blood.

Effects on the digestive and urinary tract:

The consequences of aging on the digestive system mainly include a slowing of intestinal transit by decreasing peristalsis, a decrease in acid secretion of the stomach (hypochlohydria), and a decrease in hepatic mass. Renally, there is a significant decrease in filtration rate of the kidneys, due to the loss of nephrons. In addition, the tubular function is also impaired with a decrease in the concentration / dilution of the kidney. If changes in the vesico-sphincteric system are described during aging, they do not modify the voiding function in the absence of pathology.

Effects on the skin and integuments:

Skin aging is characterized by thinning of the skin, which becomes paler and marked by lines and wrinkles. The elastic fibers are altered and the dermis is the site of fibrous thickening. These changes are more marked in areas frequently exposed to light.

The sebaceous and sweat glands are less active, resulting in skin dryness. The growth rate of skin appendages decreases with age. The hair turns gray because of the decrease in the number of melanocytes.

Effects on the sexual organs:

In women, menopause is characterized by the cessation of estrogen secretion by the ovaries, the disappearance of menstrual cycles, and the involution of the mammary glands and uterus.

The reproductive capacity disappears.

In humans, if the secretion of testosterone by the testes decreases during aging, this decrease is variable from one individual to another and occurs more gradually than the changes related to menopause. The size of the prostate increases during aging. A large proportion of older men maintain spermatogenesis that allows them to maintain reproductive capacity.

Effects on the immune system :

In general, the cellular immune response is diminished during aging. If humoral responses are preserved, the production of specific antibodies in response to vaccination is generally lower in the elderly than in the young. Despite these changes, vaccinations are effective in the elderly. Cytokine production is modified during aging with decreased production of IL-2 and IL-4 and increased production of IL-6.


Aging and psychology:

The effects of aging on psychology and relational life are highly variable from one individual to another and depend on many factors: personality, social and cultural factors, health status, life experiences, resilience …

Despite this, some experiences are shared by most of the elderly and can influence their psychic life: recomposition of social life at retirement, narcissistic crises related to the transformation of the body, death of loved ones, proximity to death . Aging leads to changes in sexuality which, contrary to popular belief, does not disappear in the elderly; these changes are strongly influenced by many factors: hormonal changes, isolation or widowhood, diseases, cultural and social factors, individual psychological profile.

In total, we can not isolate a particular psychological profile in old age. Older subjects have a psychology as diverse as that of younger individuals, but life experiences and aging have changed their psychic lives.

Aging and cognitive functions:

Cognitive functions, contrary to popular belief, are relatively unaffected by aging. Learning abilities are slightly decreased in older subjects, but this can be compensated for by the duration of learning.

Language, long-term memory, praxic and executive functions are not altered. Attentional abilities, including the ability to perform double tasks (attention divided), are altered during aging.

These effects contrast with the generally accepted notion that memory weakens as we age. These notions are due to the fact that dementias are frequent in the elderly and that their manifestations are wrongly confused with those of aging.

Aging and communication:

The communication skills of the elderly can be influenced by several situations: sensory disorders associated with aging (primarily presbycusis), and many diseases such as depression, neurodegenerative diseases with dementia, cerebrovascular diseases with language disorders.

Addictive diseases can also have an influence on the psychology of the elderly by placing the people concerned in the situation of depending on the physical plane of those around them to carry out basic acts of daily life. This situation compromises the autonomy of the individual, that is to say his ability to govern his life and can thus change the relationship between the elderly person concerned and those around him.


Lengthening of the life span:

If all ages have known very old people, we have observed for a century and a half an increase in the average life of the population. The evolution of life expectancy illustrates this phenomenon well. In France, she is currently close to 77 years for men and 84 years for women.

Several factors have contributed to this evolution: famine recession, improvement of living conditions and hygiene, progress in the fight against infectious and cardiovascular diseases.

Over the last thirty years, the increase in life expectancy has been very strongly explained by the decline in mortality among elderly and very old people.

“Grandpa-boom” effect:

The grandfather effect results from the sharp increase in the birth rate after the Second World War (from 1945 to 1975), called the baby boom. The size of this generation is particularly important and its aging will sharply increase the number of elderly subjects. This effect will be all the more spectacular as the mortality linked to the world wars has created “hollow generations”. The first “baby boomers” will turn 65 in 2010 and 80 in 2035.

Aging of the population:

A population is said to be aging if the proportion of its elderly population is increasing. The only increase in the number of elderly subjects proportional to that of young subjects would represent a balanced growth of the population without aging.

Also, aging in the demographic sense of the term implies a change in the balance of age groups in the population. In the so-called developed countries, the increase in life expectancy has led to an increase in the absolute number of elderly people. But it is essentially the decline in fertility observed since the beginning of the twentieth century that is causing the aging of the population. The age structure of a population provides a good graphic representation of the composition of a population at a given moment: the abscissa represents the number of subjects at that time (women in positive and men in negative) and the ordinate their year of birth or age. A population experiencing this phenomenon of aging is characterized by a narrowing of the base of this pyramid, while a population that does not aging has a classic pyramid shape (triangle) with a wide base.

Consequences of aging on the health of the population:

Aging has major consequences for the health of the population. Indeed, the prevalence of many chronic diseases increases with age. As a result, the number of subjects with these diseases increases in proportion to the increase in the number of elderly subjects. In addition, the progress in age and the diseases associated with it have a functional repercussion that can cause a more or less severe dependence. The prevalence rate of addiction increases with age, and the proportion of elderly who need help with one or more gestures of daily living is 14% in the 60-79 age group, 25% in 70-79 years and 65% in the over 80s. Similarly, the proportion of elderly people living in a geriatric institution also increases with age, from 5% in those aged 65 or over to 30% in the over 80s.

Has this lengthening of the life span occurred with an increase in the number of years of life in a situation of disability or, on the contrary, in conditions of independent living? By studying the evolution of disability-free life expectancy – the average number of years of life a generation can expect to live without disability – in decennial surveys, it appears that not only is the average number of years of life life with disabilities did not increase, but decreased. In other words, the increase in life expectancy achieved in recent decades has resulted in years of independent living.

Social and economic implications of aging:

The economic and social consequences of demographic aging are numerous. The issue of pensions and pensions is crucial in the French system where the contributions of active individuals – young adults – finance the retirement of elderly people. In addition, the increase in the number of elderly subjects has a direct impact on health expenditure, as, among adults, the level of consumption (per person and per year) of medical care, consultations, hospitalizations, products pharmaceutical increases with age. As a result, the demographic evolution leads to an increase in health expenditure, even if the level of expenditure per individual remains stable. Again, because of the imbalance young / old, the number of contributors to the Health Insurance does not increase in the same proportion.

Finally, the increase in the number of elderly people is leading to an increase in the need for places in geriatric institutions, particularly in residential care for dependent elderly people (EHPAD), as well as an increase in the cost of social benefits paid to the elderly, and in particular the personalized allowance for autonomy (APA) granted to elderly people with a moderate or severe loss of autonomy, or the social assistance that makes it possible to finance the stay in EHPAD or in long-term care service. people whose income does not pay for their accommodation.

In addition, the increase in the number of elderly people generates a specific economic activity: jobs in the home care sector, geriatric institutions (EHPAD), and the medico-social sector, positive action on the development of industrial sectors. related to disability and loss of autonomy (technical assistance equipment, armchairs and medical beds, tele-assistance companies, hearing aids …). Finally, the elderly also represent an important economic power, because they hold a large part of the heritage, and participate largely in the economic life, directly by their consumption and their investments but also indirectly by the financial assistance they grant to their children.

The social consequences of demographic aging lead to questions about the place of the elderly in society. More and more families have four generations, often two generations of elderly people: typically sixty-year-olds who help their octo- or nonagenarian parents, who have often become addicted.

Decreasing retirement age and improving the health status of the population have created a generation of healthy, time-sensitive young retirees, many of whom have strong professional skills. .

Some of them engage in activities that are useful for society: political life, associations, voluntary actions …

The social representation of the elderly is complex and multifaceted. A first frequent representation in traditional societies is that of the “patriarch” with wisdom and experience, source of authority and respect. Another valuable and widespread representation is that of grandparents with their role of transmission (knowledge, experience, traditions, goods …) to the youngest, and also of reference and union of the family. Others are less valued: a person weakened, ineffective, useless and unproductive, with many losses (health, beauty, sex life, work and therefore utility for society …). This type of representation contrasts with the social representation of youth or mature individuals, on the contrary valued around the same criteria. This contrast leads to consider the elderly as a burden for society. Other representations that were even more devaluing were more widespread in the past centuries, especially for older women: the wicked, “witches” … Although these representations may seem caricatured, they represent cultural stereotypes that influence, often unconsciously, the actions and the behaviors of many individuals, young and old.


Pathological aging in question:

The notion of pathological aging is not the subject of a clear definition by consensus among specialists in aging. As aging is in essence a physiological phenomenon, association with the pathological term may seem surprising at first glance. According to the authors, pathological aging corresponds either to an advance in age associated with frequent diseases in the elderly, or to a faster aging process than is usually observed, or to “borderline” states between the consequences of aging. and some diseases. In this latter approach, it is postulated that there is a continuum between some effects of aging and certain diseases (for example: cerebral aging and Alzheimer’s disease, or arterial aging and atherosclerosis). These notions are not retained in the current state of knowledge.

Successful aging:

On the other hand, the notion of successful aging or successful aging is a more consensual concept in gerontology.Successful aging describes the evolution of the health of older individuals characterized by a low rate of disabling chronic diseases, good physical and cognitive functional status, and good psychosocial functioning. Their health problems are relatively similar to those of younger adults. They are often described as vigorous elderly as opposed to vulnerable older adults. Successful aging can be understood as a process with a low loss of functional reserve capabilities, which allows resources to be mobilized in these stressful situations and to overcome them.

The understanding of successful aging is the subject of active research because “aging well” is an important issue for the health of older people and society. There is no known drug approach (vitamins, hormones, or others) that can promote successful aging in humans. Physical activity seems able to slow down or oppose certain cardiovascular, respiratory, muscular and metabolic effects of aging. Finally, cognitive stimulation programs also appear to be able to participate in the maintenance of cognitive functions in healthy elderly subjects. The effects of food are also of great interest in this area.

While nutrition appears to influence the occurrence of some age-related diseases, its effect on longevity and aging in humans is not documented. Based on these elements and some common sense, some important points can be identified to promote successful aging:

– prevent preventable premature mortality: prevention of accidents, infectious diseases, cardiovascular diseases …;

– maintain regular physical activity at any age (and start it in sedentary subjects);

– have diverse and frequent activities stimulating cognitive abilities;

– fight against social isolation and preserve / increase social activities and social network;

– have a balanced diet, rich in fruits and vegetables.


General practitioners and many specialists have an increasingly older clientele, and it is important that they are familiar with the effects of aging to better understand the health of their patients. In medical practice, the concept of vulnerability is essential because it allows us to understand the sequence of pathological situations in vulnerable elderly subjects.


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