MedicalResearch.com Interview with:
Adam Hayward PhD
Impact Research Fellow
University of Stirling
MedicalResearch.com: What is the background for this study?
Response: Adult life expectancies in industrialized countries have increased dramatically in the last 150 years, even once we’ve accounted for the fact that previously common deaths in childhood and now very rare. One hypothesis seeking to explain this increase is that childhood infections cause chronic inflammation, which are then linked with heart disease and stroke in later life, reducing lifespan.
Since such childhood infections were previously common but are now, thanks to vaccine and sanitation, much rarer, chronic inflammation should be lower and people should live longer and be less likely to die from early-onset heart disease. If this hypothesis is correct, we should see that higher exposure to infections in early life leads to increased adult mortality and deaths from heart disease and stroke.
MedicalResearch.com: What are the main findings?
Response: We tested the hypothesis using data collected from Finnish church records in the 18th and 19th centuries. We linked the child death rate from infections around the time of an individual’s birth, to their survival in later life. We found that there was no link between the child death rate from infections in early life and mortality risk in adulthood. Moreover, there was no link with deaths specifically from heart disease, stroke and cancer, and no link with later-life fertility.
MedicalResearch.com: What should readers take away from your report?
Response: Our work does not support the hypothesis that reduced childhood infections are the driving force behind increasing adult lifespan. While they do not fully refute this idea, we suggest it is most likely that factors experienced in adulthood, such as improved diet and medical care, underpin improved adult lifespan in modern societies.
MedicalResearch.com: What recommendations do you have for future research as a result of this study?
Response: The only way to definitely test this idea would be to use lifetime health records to link experience of infections in early life to morbidity and mortality in later life. This should become possible in time given the number of excellent longitudinal health studies which are being undertaken.
MedicalResearch.com: Is there anything else you would like to add?
Response: While historical data on human populations have their limitations, they do allow us to test evolutionary and epidemiological predictions in populations living at a time of natural birth and death rates, and across long timescales.
MedicalResearch.com: Thank you for your contribution to the MedicalResearch.com community.
Adam D. Hayward, Francesca L. Rigby, Virpi Lummaa. Early-life disease exposure and associations with adult survival, cause of death, and reproductive success in preindustrial humans. Proceedings of the National Academy of Sciences, 2016; 201519820 DOI:10.1073/pnas.1519820113
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