Nothing in life is more certain than this: we all grow older every day. This simple yet mysterious fact has fascinated scientists and artists for thousands of years. The philosopher Aristotle wrote more than 24 centuries ago, “All living things undergo ageing”. At that time, life expectancy was just 35 years. It keeps increasing. For those born in 2023, this number is 81 years, and is predicted to reach 91 in 2100.

No one fully understands what ageing is, or how we age. Experts on the mechanisms of ageing cannot even agree when ageing starts. Some say at conception, others at birth or at reproductive age. There are more than 300 theories about ageing, and none is fully satisfactory. However, we can say that ageing comprises all changes in our physiological structures and function over time, from conception to death.

How long can we live?

The longest documented life was lived by Jeanne Louise Calment, a Frenchwoman, who died at 123. Scientists have settled on 120 as a natural upper limit. Interestingly, average life expectancy has increased over the centuries, but maximum life expectancy has not.

Is age just a number?

There is no single answer to the fundamental question, when is somebody old? One person runs a marathon at the age of 65, while another is exhausted by crossing the room. Research suggests that perceptions of ageing have shifted; today, 80 is considered “old”, whereas just two generations ago, old age was widely accepted to begin at 60. We also know that our subjective age (what we feel) is not, for most of us, the same as our chronological age (our birthdays). The older we get, the more we feel that our bodies and especially our minds are younger than our birthdays.

New developments in medicine make it easier to determine our real biological age by analysing “biomarkers of ageing”. These include body mass index, joint mobility, certain proteins (Leptin, Interleukin6), “telomeres” (cell parts related to ageing), blood pressure.

How do we age?

Our bodies and our minds age through a process that feels different for everyone; even organs in the same body age at different rates. On average, the first changes related to ageing are seen at 20 (skin-wrinkles!), followed by changes in lung tissue, 35, in muscles and eyes, 40, in kidneys, 50, and eventually affecting all systems. In healthy individuals these changes don’t impact normal functions.

Not all ageing effects are positive or negative; having grey hair is neither good nor bad, regardless of how we feel about it! When we are seated, ageing is hardly visible between 20 and 70 years, but it is evident when we rise and walk. Chronic insult to the body, including diseases, smoking, exposure to stress, air and noise pollution, accelerates ageing. But ageing also has positive impacts. Older people achieve better scores in vocabulary tests and outperform their juniors in interpersonal tasks, particularly when experiential learning is involved.

Can we increase our life span?

Genetic inheritance from our ancestors influences life expectancy for only 10 to 15 per cent. Individual lifestyle and external influences play a much bigger role. Around the world, women live longer than men, often due to eating more healthily, using less tobacco and alcohol. In males, the hormone testosterone has been linked to risk-taking behaviour and increased incidence of cardiovascular disease.

While ageing cannot be stopped, research on laboratory animals shows it can be slowed. When mice were subjected to reduced feeds, the hungry mice lived longer. When certain old cells from aged mice were removed by genetic or drug treatment, or old mice were injected with young mice blood plasma, they lived longer, became healthier.

There is currently no known drug or treatment that extends human life span. Several drugs have shown promise: tanespimycin, rapamycin and, surprisingly, metformin – a drug treating diabetes.

Tips to help successful ageing

1,Balanced diet with lots of fruit, vegetables, wholegrains, nuts, olive oil, oily fish, small amounts of low-fat dairy and lean meat, benefiting gut microbioma, telomeres and inflammation, reducing the risk of cardiovascular disease and diabetes.

2,Healthy mouth and teeth: brushing teeth, flossing, regular dental check-ups are recommended, while sugary food is not. Drinking plenty of water helps rinse away food particles and reduce the risk of a dry mouth. Recent studies show a strong link between ageing, heart disease, diabetes, even dementia and oral health.

3,Optimal body weight: obesity is directly connected to ageing and to premature death.

4,Regular medical check-ups, including blood pressure, blood sugar, cholesterol. Keep these within a normal range.

5,Foot health: remember, the average person walks the equivalent of twice around the world in a lifetime! Cut toenails straight across and ensure your footwear fits properly.

6,Avoid chronic stress: be sensible about alcohol, and give up smoking: regardless of age, circulation, lung capacity and energy levels will improve. Smoking also increases risk of gum disease and tooth loss.

7,Hearing and eyesight tests from the age of 55.

8,Maintain social contacts to counteract loneliness and anxiety. Picking up a new or long-neglected hobby and volunteering may be helpful.

9,Keep your mind as active as your body: play new games, sports, puzzles, crosswords. Vary habits to help to create new pathways in the brain.

10,Be active, exercise daily, adopt healthy sleep habits: one study has shown exercise is the number one contributor to longevity, adding extra years, even for people who start exercising in senior years. Spending time in nature with a brisk walk for up to 75 minutes a week is associated with a gain of 1.8 years in life expectancy!

To end with another Greek philosopher, Socrates (470BC–399BC) said the secret to a long, healthy life was fourfold:

“In childhood be modest, in youth temperate, in adulthood just, and in old age prudent.”

• Sanja Malbasa-Thompson is a consultant geriatrician at King Edward VII Memorial Hospital. She has worked as a geriatrician at the John Radcliffe Hospital in Oxford, UK and teaching at Medical School in Oxford. She is coauthor of the Oxford Case Histories in Geriatric Medicine. The information here is not intended as medical advice or as a substitute for professional medical opinion. Always seek the advice of your physician