Navigating A Complex Landscape: Investigating the biology between inflammation and childhood trauma

Trigger warning: This blog discusses childhood traumatic experiences and may not be suitable for some readers.


 

It is suggested that around one in five adults may have experienced trauma in their childhood. I am sure you will agree that these are concerningly high statistics.


The reason that this is a ‘suggested’ numeric is due to the nature of childhood trauma, meaning that it’s hard to pinpoint the extent of what is happening. Those who have experienced childhood trauma may not want, or be able, to open up about what they went through, some may not recognise their experiences to be trauma.


Childhood trauma is any experience of a distressing situation in the early life, such as low socioeconomic status (perhaps living in poverty), bereavement, bullying, emotional or physical neglect, physical and sexual abuse, and more. The effects of such experiences can be carried through life, increasing the risk of negative health outcomes throughout adulthood. It is therefore really important that we conduct research to improve our understanding of such consequences so that people who have had these experiences can be best supported.


Research looking into depression frequently finds that a significant number of depressed adults may have had childhood traumatic experiences. This is an area of research that I am very interested in.


Alongside being a Writer and Co-Editor for Inspire the Mind (ITM), my day to day work is as a researcher at King’s College London. Much of my work has been looking at childhood trauma and depression and how they may or may not be connected through something called ‘inflammation.’ I recently began a PhD looking at exactly this. Last year I had the opportunity to write a short review looking at what current research is telling us about how inflammation and childhood trauma may come together in depression. This paper was called ‘Navigating a complex landscape — A review of the relationship between inflammation and childhood trauma and the potential roles in the expression of symptoms of depression.’


Photo by Victor Chaidez on Unsplash

Inflammation is a function of our immune system. When we face injury or come into contact with germs, bacteria and viruses, our immune system puts up defences and triggers lots of different inflammatory cells which try to protect us from the threats of injury or illness. In some cases, however, we find that people have inflammation levels in the body that are elevated even in the absence of threats such as germs.


Researchers have identified that some people who had experienced childhood trauma had higher levels of inflammation than people who had not, and that there was a pattern with more trauma associated with higher inflammatory levels, which was also more prominent in people who later developed depression.


Depression and inflammation is an area of research of considerable focus over the last couple of decades as we tend to see that a subgroup of people with depression have higher levels of inflammation. We do not yet fully understand the exact reason for this relationship or how it comes about biologically. But, with evidence indicating that childhood trauma increases a person's risk of developing depression later in their life, and childhood trauma and depression being associated with higher levels of inflammation both independently and together, it is important to understand how these three factors come together.


So in my paper, I looked at the literature available from previous research to see what evidence has been found to navigate, or at least try to navigate, what appears to be a very complicated landscape.


Childhood trauma, inflammation and depression


When researchers want to look at inflammation we often do so by looking at small samples of blood to observe levels of inflammatory markers which can tell us if inflammation is higher than we may expect. Researchers have shown that some of these markers, in particular, interleukin-6 (IL-6) and tumour necrosis factor-alpha (TNF-a), are higher in people with depression, but do not seem to be associated with whether these people with depression had or had not experienced childhood trauma. Interestingly though, there were some links between higher levels of these markers and more severe experiences of childhood trauma, and sexual abuse in particular. Previous reviews have found that sometimes these specific markers, IL-6 and TNF-a, can be increased in people who had experienced childhood trauma, but that this may be different depending on the type of trauma which was experienced — possibly with more physical forms of abuse such as sexual abuse specifically. But, other reviews have not always shown this same pattern so more research is needed to determine how exact this relationship is — this research was covered in a recent ITM blog.


IL-6 and TNF-a are not the only markers of inflammation however, and some studies have looked at a bigger selection. However, where higher levels of inflammation were identified, depression appeared to be driving this association, rather than childhood trauma.


Severity of depressive symptoms


Depression isn’t of course something you just have or don’t have — symptoms can be experienced at different degrees of severity. It has been found that people who had experienced multiple types of childhood trauma tended to experience more severe symptoms of depression. But does inflammation come into this too?


Comparing people with depression to people without depression, associations have been found between the severity of depression, the severity of childhood trauma and inflammatory markers, suggesting that childhood trauma impacts the immune system which then increases risk of developing depression. This work was however a small study and larger studies would need to look at this to give us more confidence in how true it may be.


Photo by Alex Lynch on iStock

What about the type of depressive symptoms?


What appears to be lacking is investigation exploring whether childhood trauma and inflammation may affect type of depressive symptoms. We see more and more research is beginning to explore these different ‘clinical profiles’ or ‘subgroups,’ as, like symptom severity, this too varies.


Different types of childhood trauma may be associated with different symptoms of depression. One study, for example, has found that emotional neglect specifically may be associated with more severe symptoms of depression which see an absence of positive mood (the technical term for this is anhedonia, that is, the inability to experience pleasurable things). Other studies indicate that people with a history of childhood trauma and depression (or siblings of people with depression) were more likely to experience symptoms of cognitive and psychomotor disturbance (for example difficulties with attention and memory, and slower movement). The study didn’t appear to find significant differences in symptoms based on the type of trauma experienced, nor did it explore inflammation.


Different profiles of depressive symptoms are often explored in the context of inflammation, with atypical depression (characterised by symptoms of over-eating and weight gain) associated with higher levels of inflammatory markers including C-reactive protein (CRP), IL-6 and TNF-a in comparison to melancholic depression (where we see an opposite profile of appetite and weight loss). However, these findings are not consistently found by others.


It would be interesting then to see these two lines of research converge.


Photo by Jordan Whitt on Unsplash

What I set out to explore turned out to be possibly more complicated than I imagined — we know that inflammation is associated with depression, and inflammation is associated with childhood trauma, and childhood trauma increases risk of developing depression, but we still need to focus more research on how this all comes together. It is especially important to do so particularly knowing the risk that is later carried through life so that we can look at how best to support the people who present this way.


I hope that it won’t be too long until there is a breakthrough in our understanding. The important thing is that there are many researchers trying to untangle the threads and will continue to work on this until we are navigating known territory, not a complex landscape.


 

Resources


Support for survivors of abuse:

Support for children and young people facing abuse:

  • Childline: Phone: 0800 1111 | Website:childline.org.uk

  • YoungMinds: Parents helpline: 0808 802 5544 | Crisis Messenger for young people (text the letters YM) : 85258 | Website: youngminds.org.uk