Could inflammation in early adulthood influence disease risk more than 30 years on?
Inflammation is part of the body's natural response to harmful stimuli, such as irritants, damaged cells, and pathogens.
The body uses this process to eliminate the threat, clear out damaged cells, and repair tissues.
Although inflammation is a force for good, if it continues for extended periods, which doctors refer to as chronic inflammation, it can lead to health issues.
Over recent years, it has become clear that inflammation can cause or advance several common diseases.
However, to date, little is known about how inflammation in early adulthood might influence health in later life.
A new research letter that features in JAMA Pediatrics investigates this question. The authors conclude that inflammation earlier in life increases the risk of cancer and cardiovascular disease 30 years later.
Inflammation in youth
To investigate, researchers from the Memorial Sloan Kettering Cancer Center in New York City, NY, and other institutions in the United States, the United Kingdom, Iceland, and Sweden took data from Swedish army conscripts.
In all, they had access to data from 248,488 conscripts to the Swedish army. These individuals were 16–20 years of age between 1952 and 1956.
From this group, the researchers removed anyone who had an existing medical issue or "marked physical weakness," which left 106,120 participants.
The participants underwent a medical exam as part of their conscription, during which the army doctors took blood samples. One of the tests assessed the erythrocyte sedimentation rate (ESR).
ESR is a nonspecific marker of inflammation that measures how quickly red blood cells settle at the bottom of a test tube of blood. A high score means that the cells sink faster than average, which is a sign of inflammation.
The researchers assigned each male's ESR scores to one of three groups: low, moderate, or high.
They followed the participants for a mean duration of 35 years, up to a maximum age of 57 years. Over this time, there were 4,835 deaths.
35 years on
The scientists identified an association between high ESR scores and an increased risk of overall mortality. Similarly, there was a link between elevated ESR and an increased risk of death from cardiovascular disease or cancer.
However, there was no such relationship between ESR and death due to alcohol or drugs, suicide, traffic accidents, or falls. The authors summarize their findings:
"In this large study, we observed inflammation during late adolescence to be positively associated with premature mortality due to cancer and [cardiovascular disease]."
Scientists have already linked inflammation to cancer and to atherosclerosis, which is the clogging up of arteries — the driving force behind cardiovascular disease. However, it is surprising that there may be signs of these relationships at such a young age.
As the authors write, "these data highlight the existence of detectable markers of premature mortality at an early stage of life."
In the earlier study, they found that participants with elevated ESR had a 63% higher risk of developing colorectal cancer 3 decades later.
Although the researchers had access to a large volume of data, the study still had limitations. For instance, the army doctors only took blood tests at one point in time, so it is not possible to know how levels of inflammation fluctuated across the decades.
Also, the researchers could not account for smoking in their analysis. However, they write that "smoking is not strongly associated with ESR" and explain that even after they excluded cancers for which smoking is a known causative factor, the results remained significant.
As the dataset only includes males, there is also the possibility that the results might not be relevant for females.
The authors hope that the findings will inspire future research, explaining that the "[r]esults demonstrate the need to better understand the role of subclinical early life inflammation in relation to later life health outcomes."
The concept that a simple blood test can measure biomarkers of mortality risk more than 30 years before death is likely to be controversial. The findings unearth many more questions than they put to bed. Scientists will need to delve deeper to confirm these surprising conclusions.