Genes are more important for life expectancy today than they were 100 years ago – here's why

But a new study, published in the journal Science, changes this picture. According to updated estimates, the influence of genes on life expectancy can reach 50–55%. The reason is not that our DNA has "strengthened", but how the world around us has changed.

Why old assessments no longer work

A hundred years ago, most people died from so-called external causes:

• infections

• accidents

• injuries

• working and living conditions

Today, in developed countries, the main causes of death are internal, age-related: cardiovascular diseases, dementia, and chronic illnesses.

To see the "pure" genetic influence, scientists analyzed the data:

• large groups of Scandinavian twins

• twins raised separately

• relatives of American centenarians

The author of the study, epidemiologist Karin Modig from the Karolinska Institute, emphasizes that this does not mean that everything is now "decided by genetics."

She offers a simple analogy with growth. A hundred years ago, a child's height was significantly affected by food shortages and childhood diseases.

Today, in affluent countries, most people get adequate nutrition. Because of this, differences in height are increasingly explained by genes, although nutrition has not disappeared as a factor.

The same thing happens with life expectancy. When:

• Medicine is improving.

• Pollution is decreasing.

• access to vaccination and quality food is increasing

— the environmental variation narrows, and the genetic contribution appears greater.

The phrase "life expectancy is 50% determined by genes" is easily misleading. In reality, heredity is not a fixed number, but an indicator that changes depending on the conditions.

For one person, genes may play a minimal role, while for another, they may play a very significant role. There are many paths to longevity: some have "protective" genetics, while others compensate for weaker genes through lifestyle, exercise, and access to medicine.