Longevity: The Complete Guide to Healthy Ageing

What is longevity, and what actually affects how we age?

Longevity simply means a long life. Healthy ageing is the more useful goal. The World Health Organization (WHO) defines it as developing and maintaining the functional ability that enables wellbeing in older age, in other words, being able to do the things you value for as long as possible.

Scientists now describe ageing as a set of connected biological processes, sometimes called the "hallmarks of ageing". A major 2023 review in the journal Cell listed twelve of them, including:

• Damage to DNA building up over time
• Shortening of telomeres, the protective caps on the ends of chromosomes
• Changes in how genes are switched on and off (epigenetic changes)
• Mitochondria, the cell's energy producers, working less efficiently
• Worn-out "senescent" cells that stop dividing but linger
• Chronic, low-grade inflammation
• Dysbiosis, an imbalance in the microbes living in and on the body

Many of these processes respond to how we live, which is where the hopeful part comes in.

How much of ageing is down to genes?

Less than many people assume, though the exact share is still debated. Classic research on nearly 2,900 pairs of Danish twins estimated that around a quarter of the variation in lifespan was heritable (about 26% in men and 23% in women).

A 2018 study of huge family trees suggested the true figure could be well below 10%, because people tend to choose partners with similar lifestyles, which makes longevity look more "genetic" than it is. More recently, a 2026 study in Science estimated a share closer to 50% once deaths from external causes such as accidents and infections are set aside.

The honest summary: genes matter, and they matter more for some people than others. But even on the highest estimates, a large part of how long and how well we live is shaped by environment and behaviour. The WHO notes that much of the variation in health in older age reflects people's physical and social environments.

What is biological age, and how is it different from your actual age?

Your chronological age is the number of birthdays you have had. Your biological age is an attempt to estimate how old your body seems based on biological markers. Two people who are both 50 can be ageing at quite different rates on the inside.

The most talked-about tools are "epigenetic clocks". These use patterns of chemical tags on your DNA (called DNA methylation) to estimate age. They have been valuable in research, where they help scientists compare groups of people and study what speeds up or slows down ageing.

What are the limits of biological age tests?

This is where it pays to be careful. A 2025 review of epigenetic clocks concluded that they are not yet ready to guide decisions about an individual person. The main issues it identified were:

• Results can vary depending on how a sample is collected, processed and analysed
• Different clocks can give different answers for the same person
• DNA methylation changes in complex ways and differs between tissues
• Clocks do not yet meet the standards expected of established clinical tests

So a biological age number is best seen as a research tool, not a verdict on your health or a prediction of how long you will live. Markers you can actually act on, such as your fitness, sleep, blood pressure and day-to-day patterns, are often more useful.

What are the key habits that support healthy ageing?

The good news is that the habits with the strongest evidence are not exotic. They are the basics, done consistently over years.

Move more, sit less

Physical activity is one of the most consistently supported habits for a longer life. A large analysis of over 36,000 adults who wore activity trackers found that people who moved the most had a much lower risk of dying during the study than those who moved the least. Even light activity was linked to lower risk.

Eat a varied, mostly plant-rich diet

The WHO recommends at least 400 g of fruit and vegetables a day (about five portions), at least 25 g of fibre, plenty of wholegrains and pulses, and limiting salt, free sugars and saturated fat. Fibre also feeds your gut microbes, which matters for ageing too.

Protect your sleep

Both too little and too much sleep have been linked to higher mortality in large studies. Regular sleep and wake times are a good place to start.

Do not smoke

The 50-year study of British doctors found that people who kept smoking died around 10 years earlier on average. Stopping at any age helped: quitting at 30 avoided almost all of the lost life expectancy, and even stopping at 60 gained around three years.

Stay connected

A review of 148 studies covering more than 300,000 people found that those with stronger social relationships had about 50% higher odds of survival over the study periods. That is comparable to some well-known lifestyle risk factors.

Manage long-term stress

Ongoing stress is linked to changes in the body that may affect ageing, which we cover in more detail below.

How does your gut affect ageing?

Your gut is home to trillions of microbes, together called the gut microbiome. They help digest food, train the immune system and produce compounds that travel around the body. The 2023 hallmarks review added dysbiosis, an imbalance in this community, to its list of ageing processes.

The gut is also closely tied to inflammation. When the gut lining and microbiome are out of balance, the immune system may stay on low alert, which is linked to the chronic inflammation seen with ageing.

One interesting study followed more than 9,000 people aged 18 to 101. It found that the gut microbiome tends to become more individual with age, and that in people around 80 and older, this pattern was linked to better health and survival. Those in poorer health did not show the same shift. This is an association, not proof of cause, but it suggests the gut is part of the healthy ageing story.

Ways to support your gut include eating a wide variety of plants, getting enough fibre and limiting highly processed foods.

→ How to Improve Your Gut Health: The Complete Guide
→ What is the Gut Microbiome?
→ How Does Your Gut Affect Your Immune System

How do your genes affect how you age?

Your DNA influences many of the systems involved in ageing. These include how well your cells repair DNA damage, how they handle stress and energy, how you process nutrients, and how strongly your body responds with inflammation.

It helps to think of genes as tendencies, not destiny. A variant linked to higher risk of a condition does not mean you will develop it, and a "favourable" variant does not protect you from an unhealthy lifestyle. Most traits linked to ageing are influenced by many genes, each with a small effect, working alongside your environment.

Where genetics can be useful is in personalisation. Knowing how your body is likely to handle certain nutrients, or whether you may have a higher tendency towards certain conditions, can help you and your doctor decide where to focus.

→ Genetic Testing for Health: The Complete Guide

What role does exercise play in longevity?

Exercise touches almost every hallmark of ageing. It supports your heart, muscles, bones, metabolism, mood and sleep. In the large tracker study mentioned above, the biggest drop in risk came between the least active group and the next group up, which suggests that moving a little more matters most for people who currently do very little.

The NHS recommends that adults:

• Do at least 150 minutes of moderate activity or 75 minutes of vigorous activity a week
• Do strengthening activities that work all the major muscles on at least 2 days a week
• Reduce long periods of sitting

Strength work deserves special mention. Muscle and bone naturally decline with age, and keeping them strong helps you stay independent and steady on your feet.

Why does tracking help?

Wearables can show your activity, resting heart rate and heart rate variability (HRV) over time. They will not make you healthier on their own, but they can help you notice patterns, such as poor recovery after hard weeks or slipping activity levels, and adjust before they become habits. Recovery matters too, because your body adapts during rest, not during the workout itself.

→ How to Improve Your Athletic Performance: The Complete Guide
→ Why Recovery Matters for Performance
→ Are Athletes Born or Made? What the Science Says

How important is sleep for longevity?

Very. Sleep is when the body carries out much of its repair and the brain clears waste and consolidates memory. A review of 16 studies with around 1.4 million people found that both short sleep and long sleep were associated with a higher risk of dying during follow-up.

Long sleep in particular may be a sign of an underlying health problem rather than a cause, so the message is not to force more hours in bed. It is to aim for regular, good-quality sleep. The NHS suggests:

• Going to bed and getting up at similar times, even at weekends
• Winding down without screens for about an hour before bed
• Cutting back on caffeine, and avoiding alcohol and large meals close to bedtime
• Keeping your bedroom dark, quiet and cool
• Staying active during the day

If you regularly struggle to sleep, or snore heavily and feel tired in the day, speak to your GP.

How does stress and inflammation affect ageing?

Inflammation is your body's natural defence against injury and infection. Problems arise when it never fully switches off. Researchers call this chronic, low-grade inflammation "inflammaging". It is considered a major risk factor for illness in older age, and most age-related diseases appear to share an inflammatory component, although exactly what causes it is still being studied.

Several things may feed inflammaging:

• An imbalanced gut microbiome
• Excess body fat, especially around the waist
• Smoking and inactivity
• Poor sleep
• Ongoing infections, including gum disease

Long-term psychological stress may also play a part. In one well-known study, mothers caring for a chronically ill child who reported the highest stress had shorter telomeres than the least stressed mothers, a difference equivalent to roughly a decade of extra ageing. This was a small study, so it shows a link, not a definite cause.

Practical ways to manage stress include regular movement, time outdoors, protecting your sleep, staying connected with people and asking for support when you need it. Looking after your gums matters too, as gum disease has been associated with heart health.

→ The Link Between Gum Health and Heart Health

Can you measure your longevity or ageing?

Not with a single number, and be cautious of any test that promises to. No test can tell you how long you will live. What testing can do is give you a clearer picture of the systems that influence healthy ageing, so you can make more informed choices.

• Your genes: A genetic test can show tendencies in areas linked to ageing, such as nutrient metabolism, inflammation and disease susceptibility. These do not change over your life, so they are useful background.
• Your gut: A gut microbiome test shows which microbes live in your gut and how diverse the community is. Unlike your genes, this can change in response to diet and lifestyle, so it can be retested over time.
• Your daily patterns: A wearable can track sleep, activity and HRV every day, helping you see how your habits affect your body.

Together these give a picture of your biology rather than a single "age" score. They work best alongside regular health checks with your GP, such as blood pressure and cholesterol.

→ Explore the Comprehensive Genetic Test
→ Explore the Gut Microbiome Test
→ Explore the PhenomeTech Ring

What can you do next?

You do not need to overhaul your life to age well. Pick one area from this guide, perhaps a daily walk, an extra portion of vegetables or a regular bedtime, and build from there. Small changes kept up over years are what the research rewards.

If you would like to understand your own biology, our Comprehensive Genetic Test looks at the tendencies you were born with, and our Gut Microbiome Test shows how your gut is doing now.

→ How to Improve Your Gut Health: The Complete Guide
→ Genetic Testing for Health: The Complete Guide