Introduction
Mental and physical health are closely intertwined: this has been known intuitively – or empirically – throughout human history. In Western tradition this is sometimes expressed through the phrase “a healthy mind in a healthy body”.1 Similarly, a holistic, mind-body-spirit approach to medicine has been seen as integral to Eastern philosophies.2
Appreciation of this connection has been increasingly supported through scientific study, which has shown an interdependence between mood and physical wellbeing.3
Perhaps the most intriguing example of the blurred line between physical and mental health, though, is inflammation. The last 10 years has brought growing evidence that inflammation plays an important role in many psychiatric disorders – even if the exact nature of the role is not yet fully understood.4,5
As this evidence grows, perhaps the question should not be: where is the line between mental and physical health? But rather: should there be a line at all?
What Is Inflammation?
Inflammation is commonly thought of as the body’s primary response to any infection, irritant, or injury. The effects of acute – or short-term – inflammation can sometimes be easily seen: for example, when the skin becomes red, warm, swollen and painful6 in response to an insect bite. Inflammation can also be chronic, or long-term: for example, the swelling and pain that people with arthritis experience in their joints.
These visible effects are driven by deeper physiological changes, including the increased production of cells and substances involved in the body’s immune response. Blood tests can reveal the existence and scale of this response by measuring what are known as “markers of inflammation”. These markers can include C-Reactive Protein (CRP) and pro-inflammatory cytokines.7,8
In short: inflammation is often considered a physical response to physical damage, which can be measured through physical blood tests.
However, it is now understood that psychological stress can also trigger significant increases in inflammatory activity – even in the absence of physical injury.9
Why Is Inflammation Being Linked to Mental Health?
The link between inflammation and psychiatric disorders has been shown in a number of ways. Some studies have focused on epidemiology: for example, patients with chronic inflammatory conditions (such as asthma or arthritis) show a high degree of comorbidity for neuropsychiatric disorders, including depression and anxiety.10
Remarkably, an association has also been found between those that have a history of early life trauma – a powerful risk factor for depression – and increased inflammation in later life.11
There have also been experimental studies: for example, psychiatric symptoms have been induced following the administration of inflammatory stimuli and, in other studies, strong associations have been found between inflammatory markers and psychiatric conditions.12,13
In particular, people with major depression have been found to have higher levels of pro-inflammatory cytokines, and C-reactive protein. In schizophrenia, many reports have described raised levels of particular cytokines, and meta-analyses have supported these findings.14
An eye-catching study published in May 2021 found that people with depression have higher levels of inflammation than those without depression, regardless of socioeconomic background, ill health or unhealthy behaviours. This finding was based on blood samples, genetic data, and physical and mental health questionnaires gathered from 86,000 patients by UK Biobank, the large-scale biomedical database.15
This was further supported by a study published a month later (June 2021), which also used the UK Biobank to review population-based data from up to 144,890 participants. That study found that CRP concentration was associated with depression scores and scores for generalised anxiety disorder.16
While the evidence is increasingly impressive, this remains an area of exciting possibility rather than settled science. The findings from some studies even suggest that, in the future, it might even be possible to distinguish between psychiatric disorders through blood tests.17
What Could This Mean for Treating Psychiatric Conditions?
The question now is whether treatments that target inflammatory pathways could be effective against psychiatric disorders.18 Evidence on this front is starting to accumulate. For example, statistically significant therapeutic effects have been shown for celecoxib – which is currently used to treat pain and inflammation in osteoarthritis – in bipolar disorder and early-stage schizophrenia.19
Some more well-known drugs are also being investigated. Aspirin, which works on an inflammatory pathway, has demonstrated some statistically significant protective and therapeutic effects in schizophrenia.20 Statins, which are best known as cholesterol-lowering treatments, also have anti-inflammatory mechanisms of action. Epidemiological studies have shown that treatment with statins is associated with a lower risk for depression.21,22
Such findings are promising, but these treatments have not yet proven their clinical efficacy. Clinical trials for these and other treatments – including anti-inflammatory drugs developed specifically for psychiatric disorders – are currently under way.23,24
Communication Will Be Key – TVF Can Help
As treatments and indications emerge that make use of the association between mental health and inflammation, one of the biggest challenges is likely to be communication. Much groundwork will be needed to break down preconceptions about the distinction between mental and physical health: including among healthcare professionals.25
TVF has extensive experience in developing clear, targeted disease awareness campaigns, as well as multimedia strategies that communicate the need for new treatments and their efficacy. Such approaches will be crucial to ensuring that much-needed new treatments for psychiatric disorders26 can fulfil their potential.
By Peter Kelly
