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Heart patients are more likely to suffer from depression, and the opposite is also true. Scientists at the University of Cambridge believe they have identified a link between these two conditions: inflammation – the body's reaction to negative environmental factors, such as stress.
While inflammation is a natural reaction necessary to fight against infection, chronic inflammation – which can result from psychological stress as well as lifestyle-related factors, such as Smoking, excessive alcohol consumption, 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 much higher risk of suffering from depression. However, scientists were unable to determine whether this was due to two conditions sharing common genetic factors or whether shared environmental factors provided the link.
"It is possible that heart disease and depression share common underlying biological mechanisms, which manifest themselves in two different conditions in two different organs: the cardiovascular system and the brain," says Dr. Golam Khandaker, an intermediate clinical researcher. Wellcome Trust at the University of Cambridge. "Our work suggests that inflammation could be a common mechanism for these conditions."
In a study published today in the journal Molecular PsychiatryDr. Khandaker and his colleague, Dr. Stephen Burgess, led a team of Cambridge researchers who examined this link by looking at data from nearly 370,000 participants in the UK Middle-aged Biobank.
First, the team examined whether family history of coronary artery disease was badociated with the risk of major depression. They found that people who reported at least one parent who died of heart disease were 20% more likely to develop depression at some point in their lives.
Next, the researchers calculated a genetic risk score for coronary heart disease – a measure of the contribution made by various genes known to increase the risk of heart disease. Heart disease is a so-called "polygenic" disease. In other words, it is not caused by a single genetic variant, but rather by a large number of genes, each of which increases the chances of developing heart disease in a moderate way. In contrast to family history, researchers found no strong badociation between genetic predisposition to heart disease and the likelihood of suffering from depression.
Together, these results suggest that the link between heart disease and depression can not be explained by a genetic predisposition common to both diseases. It rather implies that something about the environment of an individual – such as the risk factors to which he is exposed – not only increases his risk of heart disease, but at the same time increases his risk. of depression.
This conclusion was reinforced by the next stage of the team's research. They used a technique known as Mendelian randomization to study 15 biomarkers – biological "warning signals" – badociated with an increased risk of coronary heart disease. Mendelian randomization is a statistical technique that allows researchers to exclude the influence of factors that confuse or confuse a study, such as social status.
Among these common biomarkers, they discovered that triglycerides (a type of fat present in the blood) and IL-6 and CRP proteins related to inflammation were also risk factors for depression.
IL-6 and CRP are inflammatory markers produced in response to damaging stimuli, such as infection, stress or smoking. Studies by Dr. Khandaker and others have already shown that people with high levels of IL-6 and CRP in the blood are more likely to develop depression, and that the levels of these biomarkers are high in men. some patients during an acute depressive episode. High inflammation markers are also observed in people with treatment-resistant depression. This opened the prospect that anti-inflammatory drugs could be used to treat some patients with depression. Dr. Khandaker is currently participating in a clinical trial on tocilizumab, an anti-inflammatory drug used in the treatment of rheumatoid arthritis that inhibits IL-6, to determine if reducing inflammation results in an improvement mood and cognitive function of depressed patients.
Although the link between triglycerides and coronary heart disease is well documented, it is unclear why they should also contribute to depression. It is unlikely that the link is related to obesity, for example, because this study found no evidence of a causal link between body mbad index (BMI). and depression.
"Although we do not know what mechanisms are shared between these diseases, we now have clues to work on this point for the involvement of the immune system," Dr. Burgess said. "Identifying genetic variants that regulate modifiable risk factors helps to determine what actually causes the risk of disease."
The research was funded by Wellcome and MQ: Transforming Mental Health.
Dr. Sophie Dix, director of research at MQ, said, "This study brings important new information about the emergence and risk of depression, a largely under-researched area.
"Having a holistic view of a person's health, for example by jointly examining heart disease and depression, allows us to understand how factors such as traumatic experiences and the environment impact our lives. physical and mental health.
"This research clearly shows the common biological changes involved, not only opening up opportunities for early diagnosis, but also creating a strong foundation for exploring new treatments or using existing treatments differently." We need to stop thinking about mental and physical health in isolation and continue this example of bringing science together to create real change. "
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