The adult lifespan has shown a steady increase in the last decades. In the UK, a 20-year-old today is expected to live to over 80, while 150 years ago the expected lifespan was only 60. Researchers have tried for a while to determine why adult lifespan has increased so much during the last 150 years.
Previous research linked common diseases in childhood, such as smallpox, measles and whooping cough to a lower lifespan. It was thought that these diseases caused long-lasting inflammation, leading to an increased risk of cardiovascular disease in adulthood. This would ultimately result in an early death. If this were the case, the introduction of vaccines and eradication of these diseases would lead to a longer life. Children are no longer exposed to long-lasting inflammation as they rarely get these illnesses anymore.
If this hypothesis is correct, we would be able to link infections in childhood to early death from heart disease, stroke and cancer.
Evolutionary ecologists at the University of Turku and the University of Stirling re-examined the previous conclusions, but found no support for the hypothesis. Lead researcher, Adam Hayward, Impact Research Fellow at the University of Stirling, is sure that exposure to infections in early life does not lead to higher mortality risk during adulthood.
A study of 7,283 men and women born between 1751 and 1850 was undertaken by using data from church records on births, marriages and deaths collected in seven parishes in Finland. The period was chosen as it was before the introduction of effective medicine and contraception.
Based on child deaths from infections that occurred during their childhood, each person was scored on their likely exposure to disease in early life. It was assumed that if a child was born at a time when a high proportion of children died of infectious diseases, they themselves had higher exposure to disease. The link between an individual’s early disease exposure and their survival, deaths from cardiovascular disease, and their fertility was analyzed.
Researchers concluded that there was no link between an increased risk of death in later life and early-life disease exposure. The analysis also showed that there were no links to child survival rate in either men or women, number of children born, age at first birth, or risk of death specifically from heart disease, stroke and cancer.
Recent increases in adult lifespan are more likely a result of improved conditions during adulthood, such as healthcare and diet.
The full study was published in PNAS journal.