Healthy longevity: what living longer in good health means

What healthy aging means

The World Health Organization (WHO) doesn't define healthy aging as the absence of disease. In its 2015 world report it describes it as the process of developing and maintaining the functional ability that enables wellbeing in older age. Functional ability brings together the health-related attributes that enable a person to be and to do what they have reason to value.¹

That ability has two parts. One is intrinsic capacity: the combination of each person's physical and mental capacities. The other is the environment: home, neighborhood, transportation, the people around you, services. The WHO's example is clear: two people with the same physical limitation can have very different mobility if one lives near accessible transportation and the other doesn't.¹

The WHO spells out what functional ability looks like in practice: being able to move around, build and maintain relationships, meet one's own basic needs, learn, grow and make decisions, and contribute.¹ It's a broader definition than “not being ill.” The WHO itself notes that, although most older people will eventually have several health problems, old age does not imply dependence.¹

Research on aging often uses another term, “healthspan”: the period of life before the onset of chronic diseases and the disabilities typical of aging, that is, the period in good health.⁷ It's a closely related idea; the WHO's is broader because it also includes the environment.

The framework isn't merely academic. The United Nations General Assembly declared 2021–2030 the Decade of Healthy Ageing and asked the WHO to lead its implementation, with the aim of fostering longer and healthier lives.²

Years of life and years in good health are not the same

Life expectancy has risen in many countries, but that doesn't say how much of that time is lived in good health. According to the WHO, the available data suggest that the proportion of life spent in good health has remained broadly constant, which implies that the added years are not, in general, years in good health.² In its 2015 report it was more cautious: the quality of life in those extra years wasn't clear, because studies from high-income countries gave contradictory results.¹

There are different indicators for measuring that gap, and it's worth knowing what each one measures before comparing figures. In the European Union, the reference indicator is healthy life years, which Eurostat calculates from a survey question: whether, for at least the past six months, a health problem has limited you in activities people usually do.⁴

Read together, the two indicators say that, at age 65, a little under half of the remaining time in Spain was expected to be lived without limitations. Eurostat already publishes data for 2024, but it flags Spain's healthy life years with a break in series, that is, a methodological change that makes them not directly comparable with earlier years; there is no change of method for life expectancy.³ What exactly these indicators measure, how they differ from the WHO's and what the data for Spain and Europe say, we explain in life expectancy and healthy life years.

From cell to person: how to read the research

News about longevity mixes studies of very different kinds. A finding in cells, another in mice and another in people may point in the same direction, but they don't say the same thing or with the same certainty. This diagram helps place each headline.

Three questions help when you come across a headline, and each one has its own article in this guide. The first: was it seen in people or in animals?

If it was seen in animals

A review of systematic reviews traced the path of 367 therapies tested in animals for 54 human diseases. Among those with more than ten years of research behind them, 50% had reached some study in people, 40% a randomized trial and 5% approval.⁶ It's not that animals “don't work”: the positive result was often repeated in the first studies in people. But the leap to demonstrating a real benefit was the exception.

Why a result in mice, worms or cells doesn't prove a benefit in people, and what questions to ask about a news story like that, we explain in what animal studies do and don't tell us.

If it talks about “biological age”

Chronological age is the time that has passed since birth. Biological age tries to express, in years, how much an organism has changed over time compared with what is usual in a reference population.⁷ The idea has a basis: the WHO stresses that the loss of abilities associated with age is only loosely related to a person's age in years, and that there's no “typical” older person.¹

The problem is measuring it. A consensus of researchers in the field published in 2023 pointed to the lack of standards and of agreement on how to validate aging markers, and noted that none had been approved by US regulators for clinical use.⁷ That's why a “biological age” number can be interesting in research and, at the same time, unreliable as a verdict on a person.

What epigenetic clocks and similar tests measure, and what their limits are, is in biological age and chronological age.

If it promises to “cut the risk” or “add years”

A headline may say that a habit “cuts the risk of dying by 30%.” That percentage is usually a relative risk: it compares two groups with each other, but doesn't say what the starting risk was. The absolute risk does, and it's what lets you know whether the difference is large or small for a person.

It's not a technical detail. A Cochrane review of 35 studies found that, compared with the absolute reduction, the relative risk reduction is understood about equally well but tends to be perceived as larger and, above all, is more persuasive; the quality of that evidence is moderate. The authors couldn't tell whether it helps people decide better, and they warn that it can lead to misinterpreting the data.⁸

On top of that, most of the figures linking a habit to living longer come from observational studies, which show associations. One example: the figures linking daily steps with mortality. How to go from a finding like that to a question you can test in your own life, we cover in from a data point to a test, and how to read the risk figures in a headline, in relative and absolute risk.

What has backing today

Against the constant novelty of the headlines, the institutions' message is stable. The WHO sums up what each person can do like this: keeping up healthy habits throughout life, in particular a balanced diet, regular physical activity and not using tobacco, helps reduce the risk of noncommunicable diseases, improve physical and mental capacity and delay dependence on care.²

Nor is there an age after which it stops mattering. In its 2015 report, the WHO notes that the risks linked to these habits continue into older age and that reducing them is still effective, for example by improving diet or quitting smoking, although the evidence at very advanced ages is scarce. It adds that there are more and more signs that physical activity and good nutrition influence intrinsic capacity beyond preventing disease, an effect that has been studied less.¹

How to bring these recommendations into a real week has its own guides. What physical activity the WHO and Spain's Ministerio de Sanidad recommend, and how much is enough to start, is in exercise for aging with independence. What the WHO and Spain's AESAN mean by healthy eating, and how to organize it in everyday meals, is explained in the healthy eating guide. How to choose a change, make it small and keep it going, in the guide to sustainable habits. Rest isn't in the WHO sentence quoted above, but it's part of everyday life; which sleep habits have backing and which have less than it seems, we review in sleeping better.

What this guide doesn't propose

This guide doesn't recommend supplements, biological age tests or “anti-aging” protocols. It's not that everything being researched is useless; it's that, as the previous sections show, many of those proposals rest on studies in cells or animals, or on markers that aren't yet validated for making decisions about an individual.⁶⁷

Habits don't explain everything either. According to the WHO, part of the differences in health among older people is genetic, but most of it is due to their physical and social environments and to personal characteristics such as sex, ethnicity or socioeconomic position.² What this guide can offer is what's in your hands, with the backing each thing has, without promising years of life.

If you have a chronic condition, take medication, have symptoms or are considering a major change to your diet or physical activity, talk to a health professional first. This guide is general information and doesn't replace an individual assessment.