Is the excess mortality of young adults "natural"?

• Young adults have a higher mortality than the so-called "baseline" and resulting from biological constraints and epidemiological circumstances, according to our partner The Conversation.

• This excess mortality is a demographic phenomenon known for a century and a half but not fully understood, and which is often the subject of received ideas.

• The analysis of this phenomenon was carried out by Carlo Giovanni Camarda, specialist in forecasting methods (mortality, longevity, etc.), Adrien Remund, specialist in migration and historical demography and Timothy Riffe, specialist in population health.

Death can occur at any age, but not with the same probability.

It is also possible to establish the curve of death rates by age: this has a characteristic "U" shape, with a high risk of death at birth and during the first years of life, then decreasing. during childhood until reaching a minimum around 10 years.

It then goes back in life exponentially.

According to this curve, young adults should have relatively little risk of dying.

So much for the theory.

Because young adults are, in fact, often an exception and show a

higher than expected mortality

.

Is this a natural trait of the human species, or are there other factors involved?

Abnormal excess mortality

A “baseline” mortality can be estimated, which arises from biological constraints and epidemiological circumstances.

The excess of mortality of young adults in relation to this basic mortality seems to be independent of the general conditions of mortality as illustrated by the curves of death rates by age of the

(see below).

However, it is clear that between the ages of around 15 and 30, young adults often experience relatively high mortality.

We can speak of excess mortality, insofar as it adds up to the expected level.

These mortality rate curves were established for 45 countries with complete vital statistics (Here AUS: Australia, DNK: Denmark, FRE: France, JPN: Japan, NOR: Norway, PRT: Portugal, UKR: Ukraine) © A. Remund / INED via The Conversation

The absolute level of mortality observed is sometimes misleading.

For example, in 1900-1904, Danish men experienced an overall similar or even lower mortality for certain ages than their Norwegian counterparts, but unlike them suffered almost no excess mortality between the ages of 15 and 40.

At a lower level of general mortality, the curve of American men in 1990-1994 shows a very marked excess mortality which places them at the absolute level of Australia in 1940-1944, where, moreover, general mortality was much higher.

Similar observations can be made for women, although they are generally less affected.

Thus, just after the war, if Japanese and Portuguese women experience an identical general level of mortality up to the age of 15, the former then suffer a much higher excess mortality than the latter.

Forty years later, French and Ukrainian women experience a similar absolute mortality between 15 and 25 years, but which results from a high excess mortality among the former and not the latter, who also have a marked disadvantage at all other ages.

For each of the pairs considered here, young adults are therefore more vulnerable in Denmark than in Norway, in the United States than in Australia, in Japan than in Portugal, and in France than in Ukraine.

And this whatever the absolute levels of mortality between 15 and 30 years.

Excess mortality in young adults appears to be a separate component of human mortality, in addition to other processes that dictate general mortality.

If it sometimes presents a domed shape ("excess mortality bump"), as in the case of Norwegian men in 1900, it can also look more like a plateau, as observed for American men in 1990 or French women in 1980.

What can be the causes of this phenomenon?

Historically universal excess mortality?

Until recently, excess mortality in young adults was considered a universal feature of human mortality and unique to males.

These two postulates stem from a biological conception of adolescence as a tumultuous period, implicitly referring to the psychological transformations associated with puberty (production of sex hormones, asynchronous brain development, etc.).

These specificities of the “adolescent brain” would lead to a lack of inhibition, excessive risk-taking, impulsiveness, and a reduced ability to consider the consequences of one's actions.

Figure taken from A. Remund, CG Camarda and T. Riffe, 2021, Is excess mortality in young adults natural ?, Population and Societies n ° 590, p.

1-4 © A. Remund / The Conversation

These postulates only partially stand the test of the facts.

Examination of several thousand curves such as those presented above indeed shows that while excess mortality is certainly very often present in men, it can be absent or not very marked.

This was the case in the 1950s and 1960s in both Southern Europe (Spain, Portugal) and Northern Europe (Ireland, Finland).

The excess mortality bump is also observed in young women

The excess mortality of young women is systematically lower than that of young men, to the point of being absent.

However, cases with excess mortality are in the majority and correspond to very varied contexts, both at the time when maternal mortality was still high and more recently.

The interwar period seems to be marked by a particularly strong excess female mortality, both in Northern Europe (Finland, Norway) and in the South (Italy).

It could be linked to tuberculosis;

a situation that persists beyond World War II in Japan and Bulgaria.

More recently, excess mortality has been observed in early adulthood, which is particularly marked in several Western countries (France, United States or New Zealand).

Figure taken from A. Remund, CG Camarda and T. Riffe, 2021, Is excess mortality in young adults natural ?, Population and Societies n ° 590, p.

1-4 © A. Remund / The Conversation

In reality, for women, only the 1950s and 1960s seem to be free from any excess mortality.

The excess mortality is therefore not a universal phenomenon nor specific to men.

An increase in violent deaths during puberty?

Another corollary of the biological conception of adolescence is that the excess mortality of young adults is thought to be due to an increase in dangerous behavior in the years following puberty.

The expression “

is also often used, some authors making an explicit link between excess mortality and puberty, which would lead to “risky” behavior leading to an increase in violent deaths.

Here too, this explanation only partially stands up to the test of the facts.

First, from the point of view of the ages concerned, if the bump starts well at the beginning of adolescence, it manifests itself until the thirties, that is to say well after the end of puberty.

In the United States, it disappears around 35 years for men and 25 years for women in the 1960s. This limit then increased for both sexes until reaching 45 to 50 years in the early 1990s, especially under the influence of HIV which kills later than accidents.

It has fluctuated for between 30 and 40 years, in part due to the epidemic of opioid overdoses.

Such a spread beyond adolescence is not compatible with a purely biological origin.

Then, the detail of the causes of death is more complex than it seems.

For example, in the United States, traffic accidents, which contributed about 60% of excess mortality in the 1960s, now represent only a quarter among men, or as much as suicides and homicides.

And for both sexes, the contribution of overdoses has increased from almost 0% to 20% of excess mortality during the last decade.

The role of tuberculosis

Finally, historically, violent causes have not always been the most important.

In the 22 countries for which causes of death are available for older periods, pulmonary tuberculosis was, until the middle of the 20th century, the main source of excess mortality in young adults.

In the interwar period, it still contributed about 50% of excess mortality among men.

The proportion going up to 90% in Portugal, and from 70% to 90% in Sweden, Spain, France, England, Greece, Italy, the Netherlands and Norway.

At the same time, maternal mortality was at the origin of only less than 10% of the excess mortality of young women, with the exception of certain non-European countries (United States, Canada, Chile, New Zealand and Taiwan) where it still represented 30% to 40% before the 1940s.

Violent deaths (suicides, homicides, accidents) surpass tuberculosis between 1940 and 1960 depending on the country.

This turnaround coincides with on the one hand the spread of antibiotics (streptomycin, which makes it possible to fight against tuberculosis, was discovered in 1944), and on the other hand the democratization of motorized means of transport.

The importance of violent deaths is therefore a relatively recent phenomenon.

Our "MORTALITY" dossier

A phenomenon still poorly understood

The “bump” of excess mortality among young adults is a demographic phenomenon known for a century and a half but not fully understood.

Its examination is sometimes the object of received ideas which are based on a purely biological conception of adolescence, assuming its universal character, gendered and linked to “risky” behaviors.

Recent studies have made it possible to better define its main characteristics: not universal and more masculine, without however escaping women.

Violent deaths only partially explain this.

Without completely ruling out biological factors, the transition to adulthood plays an essential role in concentrating a significant number of socio-economic risk factors in a short and critical period of the life course.

Health

Well-being: Why is meditation attracting more and more young adults?

Health

Mental health: Why victims of mental health problems age (and die) prematurely

This analysis was written by 

, doctor, specialist in forecasting methods (mortality, longevity, etc.) at the National Institute of Demographic Studies (INED),

, doctor, specialist in migration and historical demography at the University of Groningen (Netherlands) and

, doctor, specialist in population health at the University of the Basque Country / Euskal Herriko Unibertsitatea (Leioa, Spain).

The original article was published on 

.

Declaration of interests

●

●

●

• Accident

• Youth

• Mortality

• The Conversation

• Podcast

• Society