When do we start to age? Can the ageing process be stopped? How do we grow old in a healthy way? Here we answer the most important questions about ageing.

What do the terms life expectancy, lifespan, longevity and health span mean?

Even if some of these terms sound interchangeable, it is important to know the exact definition. Life expectancy describes the time a living being is expected to live, based on the year of birth, as well as on their current age and various demographic factors, including gender. It is always defined statistically as the average number of years of life remaining at a given age. Life expectancy is therefore basically the average lifespan of a population. In contrast, the maximum lifespan is the maximum time that one or more members of a population can survive between birth and death. The oldest woman in the world lived to be over 122 years old, which is why the maximum human lifespan is often given as 120 years.  The term longevity describes the ability to live a long life. Longevity can be regarded as the average lifespan under ideal conditions. The term health span describes the period of time during which a person is healthy within his or her lifetime. The health span is therefore shorter or at most as long as the lifespan and a person can fall ill early in life but still live for several years.

When does ageing begin?

From a cell biological point of view the ageing process begins with the division of the fertilised egg cell, i.e. before birth. The classic signs associated with ageing, such as the appearance of wrinkles or the decrease in performance and stamina, become visible from around the age of 20. However, scientific studies show that every person ages differently. Ageing is therefore an individual process.

What is biological age?

If you are asked about your age you usually give your chronological age, i.e. the number of years you have lived. However, the chronological age does not say much about the current status of the body: while one person can still run a marathon without any problems at the age of 50, the other is already exhausted from climbing stairs to the first floor. In order to find out what state the body really is in the biological age can be determined. To do this, various indicators of the human body are analysed, so-called biomarkers. Biomarkers of aging are features that allow a better prediction of the actual functioning of the organism at a higher age and are more reliable than chronological age. These include, for example, blood pressure, vision, hearing and joint mobility. In addition, the length of the telomeres and certain proteins in the bloodstream are among the measurable biomarkers. Probably the best-known biomarker measurable in the blood is cholesterol, but certain inflammation markers are also suitable for determining biological age. Another biomarker that enables the determination of biological age is the epigenetic clock. The values of these biomarkers together give an estimated biological age.

What is the epigenetic clock?

Epigenetics deals with chemical and structural changes in the genetic material that do not affect the sequence of DNA building blocks, but regulate how genes are read. These changes can be caused by environmental influences, among other things, and are responsible, for example, for the differences between identical twins whose DNA sequence is the same. Epigenetic changes can serve as biomarkers for the age of a person because they are passed on during cell division. The ageing researcher Steve Horvath discovered that the pattern of epigenetic markers in the genome changes in ageing cells. This pattern, known as the epigenetic clock, can be used to determine a person's biological age, which may soon help improve diagnoses and disease classification in medical research.

What role do genes play?

The genetic predisposition of each individual has an influence on the ageing process and thus on personal life expectancy. If the life span of identical twins in humans is compared the influence of genes can be estimated to be around 10-15 percent. In comparison to genes, individual lifestyle and external influences play a much more decisive role in ageing.
In some model organisms genes are known to have a direct influence on maximum life expectancy. In both the worm Caenorhabditis elegans and the fruit fly Drosophila melanogaster the inactivation of certain genes even leads to a doubling of life span. However, the fact that such life-prolonging gene mutations have not become established in the wild suggests negative effects of the gene mutations that overshadow the benefits of long life.

Why do women live longer than men?

On average women live longer than men, almost 8 percent! And this is not only the case in humans, but also in many other mammalian species, where life span differences are as high as 20 percent. The higher life expectancy of women is often attributed to the fact that women generally eat healthier food and pay more attention to their health. On average, women go to the doctor earlier and more often than men, they usually drink less alcohol, consume less tobacco and pay more attention to a healthy diet. In addition, statistics on life expectancy include suicide cases, which are five times more common among men than among women. But there is also a genetic component that makes women live longer. The advantage for women is the double X chromosome. While women have two X chromosomes, men have one X chromosome and one Y chromosome. Important genetic information of the X chromosome is therefore duplicated in women and can compensate for possible gene mutations and defects of the other X chromosome. This is not the case in men and is responsible, for example, for the red-green vision deficiency that occurs much more frequently in men. The decisive factor for ageing is that the X chromosome also contains gene segments that influence the body's immune system. If these gene sections are defective in men they cannot be compensated for by a second, faultless X chromosome. In addition to the different sex chromosomes, the influence of gender-specific hormones on the ageing process is also discussed. A possible connection between the hormone testosterone and the increased rate of cardiovascular diseases in men is suspected.

What happens in our bodies in old age?

Everyone knows the classic signs of ageing such as grey hair and wrinkles. However, some signs can be detected much earlier. At around 15 years of age the elasticity of the lens of the eye begins to diminish and it becomes increasingly difficult to focus over the years. Already from the age of 20 many classic signs of age become noticeable on the human body. Wrinkles become visible because the skin loses its elasticity due to the loss of collagen, elastin and hyaluronic acid. Endurance decreases because the production of the pulmonary alveoli decreases, resulting in a smaller breathing volume and less oxygen entering the blood. The number of hair cells in the cochlea decreases, which means that we hear high-pitched sounds increasingly poorly. At the age of 25 fertility decreases in women and testosterone levels decrease in men. A little later the sperm density also decreases in men. From the age of 30 the elasticity of the cartilage slowly decreases and certain movements become more difficult. From this time on the intervertebral discs also become thinner. From the age of 35 the first grey hairs become visible, because the production of melanin slows down and later even stops completely. At about 40 years of age thickening of the lens and loss of lens flexibility (presbyopia) takes place and reading becomes more difficult. From the age of 55 onwards muscle loss increases and the body changes its muscle/fat ratio towards fat. The ageing process is now noticeable because the blood vessels calcify and consequently blood pressure rises. The first organs such as kidney and liver begin to function less efficient, which means that the body's detoxification progresses more slowly. As we grow older, neurodegenerative diseases such as dementia (for instance Alzheimer’s disease), Parkinson's disease, cardiovascular diseases and cancer become more common, to name but a few of the most common age-associated diseases.

Can ageing be slowed down?

Different approaches are being pursued in ageing research to slow down the ageing process. Although some results seem promising, the methods under investigation are still far from being applied in human medicine. For this reason, we can so far only refer to scientific studies on model organisms or still open studies with patients.

Young intestinal bacteria

At the Max Planck Institute for Biology of Ageing Dario Valenzano researches the influence of intestinal bacteria on the ageing process. His research group is investigating the ageing process on the turquoise killifish and has been able to show that old fish remain active for longer and live up to 40 percent longer if they maintain the intestinal bacteria of young fish. The composition of the microorganisms in the fish's intestines, the so-called intestinal flora, thus seems to have a direct influence on the ageing process. Among other things the microorganisms influence food intake, metabolism and immune defence. With age the composition of the bacterial community in the gut changes. The variety of bacteria that ensure a healthy intestine in youth decreases and among the bacteria still present there is a larger proportion of pathogens. How exactly the intestinal bacteria influence life span is the subject of current research in Dario Valenzano's research group. The interesting thing is that the intestinal flora of the turquoise killifish shows great similarities with that of humans, which means that the results are also important for human ageing.

The "vampire" treatment: young blood

Researcher Tony Wyss-Coray of Stanford University found that the transfer of blood from younger mice to older mice had a rejuvenating effect on them. The older mice were no longer as frail and their brains were also more powerful again, which Wyss-Coray attributes to the effect of certain proteins in the blood plasma. However, until now, no one has convincingly shown that young blood lengthens lives, and there is no promise that it will.

Reactivating the thymus gland with growth hormones

In a study of nine men between 51 and 65 years of age the biomedical scientist Greg Fahy tried to reactivate the thymus gland to stop the aging process. The thymus is an organ located under the breastbone in which defence cells are produced. This is where the immune system is formed and trained. However, from the age of about 60 this system weakens, making the person more susceptible to infections and diseases. Greg Fahy regularly administered three different substances, including a growth hormone, to the test persons for one year and in this way reactivated the thymus gland. However, not only did the test subjects grow new thymus tissue, but also their immune cell profile eventually resembled that of a much younger person. Within the one-year treatment period, the test persons biologically became 18 months younger. With just nine - exclusively male - study participants and without long-term observation of the possible consequences of the treatment this study should be treated with caution.

How to grow old in good health?

The positive influence of a healthy, balanced diet, sufficient sleep and exercise on the ageing process is not only a generally known assumption, but is supported by many scientific studies. On the other hand, stress and the consumption of alcohol or cigarettes are among the factors that prevent healthy ageing. However, non-biological influences are also of decisive importance for the ageing process, such as the living situation, the level of education and the social and family environment. Anyone who wants to do something to grow old in a healthy way should make sure they maintain a healthy diet, stay physically fit, get enough sleep and avoid alcohol and cigarettes. If possible, avoid chronic stress and maintain social contacts.
The Mediterranean diet can be seen as a "recipe" for healthy eating: it is based on a low-meat diet, lots of fruit, vegetables and nuts, fish and olive oil. Studies show that such a Mediterranean diet has a direct influence on the composition of intestinal bacteria. This reduces the frequency of harmful bacterial species and at the same time increases the number of bacteria with health-promoting properties. In addition, volunteers on a Mediterranean diet showed longer and more intact telomeres and a lower level of inflammatory markers was found in the blood. The consumption of fresh fruit and vegetables also reduces the risk of chronic diseases such as diabetes or cardiovascular disorders.

What are "blue zones"?

The term "blue zone" describes regions of the world where people live longer than average and in good health, and where particularly many centenarians live. Five regions are currently known as "Blue Zones": Okinawa (Japan), Sardinia (Italy), the Nicoya Peninsula (Costa Rica), Ikaria (Greece) and Loma Linda (California, USA). All five regions have certain cultural similarities, which are used as an explanation for the long and healthy life. These include a predominantly plant-based diet and frequent consumption of vegetables, moderate calorie intake and low consumption of tobacco and alcohol. In addition, the inhabitants of "blue zones" hold family as particularly important, social commitment is very pronounced and sport activities are an integral part of life. Social cohesion, community and care thus seem to be decisive factors for healthy ageing, alongside a balanced diet and a healthy lifestyle.

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