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 [1]. The term longevity describes the ability to live a long life beyond the species-specific average age of death [2]. 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 [3].


  1. Dong, X., B. Milholland, and J. Vijg, Evidence for a limit to human lifespan. Nature, 2016. 538(7624): p. 257-259.
  2. De Benedictis, G. and C. Franceschi, The unusual genetics of human longevity. Sci Aging Knowledge Environ, 2006. 2006(10): p. pe20.
  3. Kaeberlein, M., How healthy is the healthspan concept? Geroscience, 2018. 40(4): p. 361-364.

When does ageing begin?

In general, one can say that ageing starts after development at a time point when the body is mature. In humans this can be set around the age of 20 years. This is the time the classic signs associated with ageing become visible, such as the appearance of wrinkles or the decrease in performance and stamina. The speed with which every person ages might be different, mainly as a result of different environmental factors and the contribution of the genetic predisposition. However, the general ageing processes responsible for ageing are probably the same between individuals.

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 ageing 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 [1]. 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 [2]. Another biomarker that enables the determination of biological age is the epigenetic clock [3]. The values of these biomarkers together give an estimated biological age.


  1. Jazwinski, S.M. and S. Kim, Examination of the Dimensions of Biological Age. Front Genet, 2019. 10: p. 263.
  2. Jylhävä, J., N.L. Pedersen, and S. Hägg, Biological Age Predictors. EBioMedicine, 2017. 21: p. 29-36.
  3. Horvath, S. and K. Raj, DNA methylation-based biomarkers and the epigenetic clock theory of ageing. Nat Rev Genet, 2018. 19(6): p. 371-384.

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. 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. The pattern of DNA methylation, a specific epigenetic mark, changes in ageing cells [1]. The ageing researcher Steve Horvath developed an algorithm to extract DNA methylation sites that can predict biological age. His epigenetic clock bases on a set of 353 DNA methylation sites sufficient to precisely predict biological age in different cells and tissues [2]. 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.


  1. Bocklandt, S., et al., Epigenetic predictor of age. PLoS One, 2011. 6(6): p. e14821.
  2. Horvath, S., DNA methylation age of human tissues and cell types. Genome Biol, 2013. 14(10): p. R115.

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 [1]. 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 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 [2, 3]. 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.


  1. Melzer, D., L.C. Pilling, and L. Ferrucci, The genetics of human ageing. Nature Reviews Genetics, 2020. 21(2): p. 88-101.
  2. Piper, M.D.W. and L. Partridge, Drosophila as a model for ageing. Biochim Biophys Acta Mol Basis Dis, 2018. 1864(9 Pt A): p. 2707-2717.
  3. Tissenbaum, H.A., Using C. elegans for aging research. Invertebr Reprod Dev, 2015. 59(sup1): p. 59-63.

Why do women live longer than men?

Everywhere in the world women live longer than men [1]. And this is not only the case in humans, but also in many other mammalian species [2]. 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 [3, 4]. In addition, statistics on life expectancy include suicide cases, which are significantly more common among men than among women [5, 6]. But there may also be a genetic component that makes women live longer. The advantage for women could be the double X chromosome [2]. 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 may be that the X chromosome also contains gene segments that influence the body's immune system [7]. 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 sex-specific hormones on the ageing process is also discussed. Thus, a possible connection between the hormone testosterone and risky behaviour as well as the increased rate of cardiovascular diseases in men is suspected [8, 9].


  1. Esteban Ortiz-Ospina, D.B. Why do women live longer than men? Our World in Data 2018.
  2. Xirocostas, Z.A., S.E. Everingham, and A.T. Moles, The sex with the reduced sex chromosome dies earlier: a comparison across the tree of life. Biology Letters, 2020. 16(3): p. 20190867.
  3. Griswold, M.G., et al., Alcohol use and burden for 195 countries and territories, 1990-2016: a systematic analysis for the Global Burden of Disease Study 2016. The Lancet, 2018. 392(10152): p. 1015-1035.
  4. Oksuzyan, A., et al., Sex differences in health and mortality in Moscow and Denmark. European Journal of Epidemiology, 2014. 29(4): p. 243-252.
  5. Kiely, K.M., B. Brady, and J. Byles, Gender, mental health and ageing. Maturitas, 2019. 129: p. 76-84.
  6. Miranda-Mendizabal, A., et al., Gender differences in suicidal behavior in adolescents and young adults: systematic review and meta-analysis of longitudinal studies. International journal of public health, 2019. 64(2): p. 265-283.
  7. Libert, C., L. Dejager, and I. Pinheiro, The X chromosome in immune functions: when a chromosome makes the difference. Nature Reviews Immunology, 2010. 10(8): p. 594-604.
  8. Roberts, M.L., K.L. Buchanan, and M.R. Evans, Testing the immunocompetence handicap hypothesis: a review of the evidence. Animal Behaviour, 2004. 68(2): p. 227-239.
  9. Stanton, S.J., S.H. Liening, and O.C. Schultheiss, Testosterone is positively associated with risk taking in the Iowa Gambling Task. Hormones and Behavior, 2011. 59(2): p. 252-256.

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. 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.


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.

How to grow old in good health?

The positive influence of a healthy, balanced diet on the ageing process is not only a generally known assumption, but is supported by many scientific studies [1, 2]. In addition, sufficient sleep and exercise have a positive impact on age-related health parameters [3, 4]. On the other hand, chronic stress and the consumption of alcohol or cigarettes are among the factors that prevent healthy ageing [5, 6]. 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 [7, 8]. 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 [8, 9]. The consumption of fresh fruit and vegetables also reduces the risk of chronic diseases such as diabetes or cardiovascular disorders.


  1. Moore, K., et al., Diet, nutrition and the ageing brain: current evidence and new directions. Proceedings of the Nutrition Society, 2018. 77(2): p. 152-163.
  2. Pallauf, K., et al., Nutrition and Healthy Ageing: Calorie Restriction or Polyphenol-Rich “MediterrAsian” Diet?Oxidative Medicine and Cellular Longevity, 2013. 2013: p. 707421.
  3. Chaput, J.P., C. Dutil, and H. Sampasa-Kanyinga, Sleeping hours: what is the ideal number and how does age impact this? Nat Sci Sleep, 2018. 10: p. 421-430.
  4. Garatachea, N., et al., Exercise attenuates the major hallmarks of aging. Rejuvenation Res, 2015. 18(1): p. 57-89.
  5. Meryl, H.K., et al., How Environmental Agents Influence the Aging Process. Biomolecules & Therapeutics, 2009. 17(2): p. 113-124.
  6. Schou, A.L., et al., Alcohol consumption, smoking and development of visible age-related signs: a prospective cohort study. J Epidemiol Community Health, 2017. 71(12): p. 1177-1184.
  7. Garcia-Mantrana, I., et al., Shifts on Gut Microbiota Associated to Mediterranean Diet Adherence and Specific Dietary Intakes on General Adult Population. Front Microbiol, 2018. 9: p. 890.
  8. Ghosh, T.S., et al., Mediterranean diet intervention alters the gut microbiome in older people reducing frailty and improving health status: the NU-AGE 1-year dietary intervention across five European countries. Gut, 2020. 69(7): p. 1218.
  9. Boccardi, V., et al., Mediterranean Diet, Telomere Maintenance and Health Status among Elderly. PLOS ONE, 2013. 8(4): p. e62781.

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) [1]. 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 [1].


  1. Buettner, D. and S. Skemp, Blue Zones: Lessons From the World's Longest Lived. Am J Lifestyle Med, 2016. 10(5): p. 318-321.

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