It was in 2015 that the WHO redefined health ageing. They wanted to move away from a disease-based assessment. Instead, they want to focus on how well individuals function in their everyday lives. Those functional abilities that enable individuals to do what they value.

The disease-based approach views an individual as the sum of their illnesses. According to the WHO it fails to recognize the complexity of the needs of older individuals. They will often experience multiple chronic diseases. The result can be a separate set of symptoms. These cannot be forecast from simply combining individual diseases. Modern medicine enables individuals to function with diseases. Previously they would have debilitated them. Age brings with is frailty and sarcopenia. These are often neglected in disease-centered approaches.

A functional approach brings with it added complexity. Being able to function is partly dependent on the environment. If the individual is “ageing at home” then they may be able to function normally. Move that person to an institution and they may lose that functionality. There is no standard definition of what an individual may value. It is idiosyncratic.

Defining Functional Capacity

Diseases are easy to track. Records exist within healthcare systems, and the progression of each disease is understood. Defining “functional ability” is much more complex. Since 2015 teams have been trying to define its components and to find ways to measure it. As a starting point the teams have defined five core domains:

Cognitive Functioning: Includes basic practical things like memory, spatial awareness and even remembering the date.

Locomotion: The ability to be able to get around. It can include simple tests of rising from a chair.

Vitality: Includes basic things like loss of appetite or weight, eating and nutrition. Respiration and cardio capacity. How much “energy” you have.

Psychological: Includes assessment of mental state. Of depression, the senses of hopelessness or conversely an interest in doing things.

Sensory: Includes a basic assessment of all senses. Can the individual function alone or with the aid of glasses or hearing aids?

Studies using longitudinal data are validating these domains. Individuals view the different domains as separate. Scores on the domains predict relevant functioning issues later in life.

The Intrinsic Capacity Idea.

At any giving point in our life our functional ability depends on our intrinsic capacity. Like the roots of a flower, intrinsic capcity provides the resources for ability to blossom. We build up a level of capacity when we are young. That is depleted as we age. If we can build more capacity when we are younger, then age will take longer to have an impact on us. We can maintain our functioning longer. Building intrinsic capacity involves things like stopping smoking, eating well etc. This takes the “functioning” idea beyond the treatment of older people.

Intrinsic Capacity Across the Generations.

Medical definitions of ageing suggest that the period of ill health at the end of life is growing. This is hardly surprising. The incidence of all diseases and especially chronic diseases increases with life expectancy. What happens if we take a functional approach? Newsletter #226 What's Happenning to Healthy Ageing?" suggested that that the period of disability is at worse static and could be compressing.

A new UK study published in early 2025 “validates” the domains of functioning. More importantly it confirms that compression is taking place. The study uses the large scale ELSA longitudinal survey. It provides data on 14,710 people over their lifetime. The questionnaire used could not have been designed with “intrinsic capacity” in mind. It was created long before the emergence of “functional ability” as an idea. However, these are large surveys with many questions. It was therefore possible to create a surrogate questionnaire, retrospectively. This covered the different domains.

The results were positive and enlightening. People were staying younger longer. A sixty-eight-year-old born in the 1950’s had the intrinsic capacity of a 62-year-old in the 1940’s cohort. That is a massive improvement in a decade. The results are comparable to the findings using a frailty index. (See Newsletter #178 "A Picture of Healthy Ageing"). The results were visible across all domains and were not biased by any particular domain.

The innovation in this study is that it could explain why the curves are moving. Each generation started ageing from a higher base. Each had a higher intrinsic capacity before any decline. Even with the same rate of decline this would have generated a cohort effect. However, they also found the rate was less. Each successive cohort was declining more slowly. The result was that there was compression. The period of ill health at the end of life was less for each successive generation. The findings held across the sexes.

Understanding Why Statistics were Created

Governments and NGO’s collect data for different purposes. They are very specific in the words that they use. There is a world of difference between a period life expectancy and a cohort expectancy.(Newsletter #132 "Life Expectancy is not a Forecast". Period Life expectancy is a benchmark for asssessing the success of health policy. Cohort Life expectancy is used to forecast the future state of Society. We all need to get our terms clear. We need to understand what a number means. No less so than when trying to understand what will happen to us in the last few years of life. Functional data is very different from disease based data.

We are the first generation that will live into our nineties. We will get chronic diseases that cannot be cured. The symptoms can however be alleviated. We can adapt our homes to live a relatively normal life. At some point, frailty will catch up with us. That period of lost functionality is not growing. If anything, it is shrinking. We are living healthier for longer.

PS. After two sessions with my trainer, Kieran, this week I can confirm what a good guy he is. He forgave me for spelling his name wrongly. No extra push ups!