Inflammation links heart disease and depression: Study

As part of a recent study, researchers have found links between heart disease and depression.

According to the findings, people with heart disease are more likely to suffer from depression, and the opposite is also true.

The study also suggests that while inflammation is a natural response necessary to fight off infection, chronic inflammation - which may result from psychological stress as well as lifestyle factors such as smoking, excessive alcohol intake, physical inactivity and obesity, is harmful.

The link between heart disease and depression is well documented. People who have a heart attack are at a significantly higher risk of experiencing depression. Yet scientists have been unable to determine whether this is due to the two conditions sharing common genetic factors or whether shared environmental factors provide the link.

"It is possible that heart disease and depression share common underlying biological mechanisms, which manifest as two different conditions in two different organs - the cardiovascular system and the brain. Our work suggests that inflammation could be a shared mechanism for these conditions." said Golam Khandaker, lead author of the study, published in the journal of Molecular Psychiatry.

The team of researchers examined the link between the three by studying data relating to almost 370,000 middle-aged participants of UK Biobank.

First, the team looked at whether family history of coronary heart disease was associated with risk of major depression. They found that people who reported at least one parent having died of heart disease were 20% more likely to develop depression at some point in their life.

Next, the researchers calculated a genetic risk score for coronary heart disease - a measure of the contribution made by the various genes known to increase the risk of heart disease. Heart disease is a so-called 'polygenic' disease - in other words, it is caused not by a single genetic variant, but rather by a large number of genes, each increasing an individual's chances of developing heart disease by a small amount. Unlike for family history, however, the researchers found no strong association between the genetic predisposition for heart disease and the likelihood of experiencing depression.

Together, these results suggest that the link between heart disease and depression cannot be explained by a common genetic predisposition to the two diseases. Instead, it implies that something about an individual's environment - such as the risk factors they are exposed to - not only increases their risk of heart disease, but at the same time increases their risk of depression.

"Although we don't know what the shared mechanisms between these diseases are, we now have clues to work with that point towards the involvement of the immune system. Identifying genetic variants that regulate modifiable risk factors helps to find what is actually driving disease risk," said Stephen Burgess, lead researchers of the study.