A recent article in the New Scientist suggests that we age by instalment (1). That there are break points in our ageing. We will remain in the same state of ageing for up to 20 years. There will then be a “tipping point” and ageing accelerates. It then reaches a new “steady state”. The researchers suggest that such changes occur at the age of 40, 60 and 80.

What do we know about the shape of the ageing curve?

The Ageist View

We should be able to rule out the ageing curve implicit in ageism. It assumes that we reach a “magic age”. It could be anywhere between 50 and 70. On our birthday we become “old”. We join an amorphous group of “grey identical individuals". We are “dear but doddery”. Kind to others but losing our physical and mental abilities. There is a step in the curve downwards. All the evidence is against this. Despite that we all still implicitly believe the model to an extent.

The Frailty View

Many authors have recognized that there is a period at the end of life where things start to go wrong. Frailty indexes put together many different measures. Each represents one of the small failings that constitute ageing. They can include cognitive measures. They can include measures of physical strength and flexibility. They will often include self-reported measures of coping with the tasks of life. Newsletter #178 "A Picture of Healthy Ageing"

All show the same pattern. A relatively slow growth in frailty that accelerates in the last 10-12 years of life. The growth is exponential. Few people reach frailty indices above 0.6 (out of 1). Such a ten year period has been called “the fourth age”. The same author defines four ages. The first age is about learning and building capability. The second age is about using those capabilities. To increase personal happiness and prosperity. The age of work, families and homes. The third age is “retirement”. The reduction of work.

The Blood Protein View

Recent advances in the analysis of blood proteins have identified biomarkers of age. These are proteins known to change with age. Often, they are associated with the subsequent onset of chronic disease. There was a surprising finding when looking at these biomarkers. The different systems in the body age differently for different people. Individuals vary and the systems in their bodies are at different stages of ageing.

These studies use longitudinal data. It is possible to relate how these “systems” age to the onset of different diseases. For example, enhanced “respiratory system” ageing can later lead to many related chronic diseases such as emphysema. There is not a single ageing curve but rather curves for different parts of the body. Recent research has highlighted the importance of the brain’s ageing. It seems to have a far bigger impact on overall ageing than the other systems.

Ageing by Instalment

Researchers are finding that some of our abilities “wear out”. We reach a certain age, and we can no longer produce a particular enzyme or protein. We can no longer replace our dying blood cells at the same rate. At a micro level this is the same model of ageing suggested by the World Health Organization. It is the accumulation of minor failings in our physiology. The cumulative effect eventually catches up with us.

The surprising finding is that these failures seem to occur in batches at different ages. We are ageing by instalment. At 40 the researchers suggest that our tolerance for alcohol can suddenly decline. We are more likely to have a hangover in the morning.

It seems that the blood proteins do not follow a linear downward trend. Instead there are waves with three large peaks. These are at the ages of 34, 60 and 78. Each wave largely consist of different proteins. Each is associated with different set of biological functions. The researchers argue that the changes could be due to the environment in which we live or to our genetic make up.

This seems inconsistent with other findings on the ageing curve and how we all age differently.

Idiosyncratic Ageing

Most other evidence suggests that we all age differently. There should not be step functions in our ageing at fixed chronological ages. People age at different rates. We all know of people who are “young for their years”. The data supports this view. The frailty studies show huge variations in results for people of the same chronological age. The best performing ninety-year-olds have the same frailty scores as badly performing fifty-year-olds.

In these Newsletters I have discussed the huge variation in cognitive ability at a given age. There are (#103) superagers who maintain the memory capacity they had when they were fifty. At ninety they can remember the same things. Cognitive ability depends on the environment in which we grow. It is influenced by our usage of our abilities.

Much to learn

In previous Newsletters I have discussed the genome and the exposome (#106). Many studies of twins have suggested that our genes account for only 15% of our health. The balance comes from our environment throughout our lives , our exposome. In fact, it is from the moment of conception. This may be the explanation for the different ageing curves. The existing "instalment" studies may be tapping into the 15% controlled by our genes. Logically some declines must be associated to chronological age. Research continues.

(1) New Scientist 12 July,2025 Ageing, Fast and Slow