Vishvajyth Ponnambalam
As we continue to move on from the Covid-19 pandemic, researchers and health professionals are still searching for answers regarding the multi-faceted novel virus that brought the entire world to a standstill a few years ago. Now, new research has been published linking Long Covid to low serotonin levels in the blood. But what exactly is Long Covid? According to the NHS, Long Covid is when some of the symptoms of Covid 19, such as fatigue, loss of smell and shortness of breath persist in patients even after 12 weeks, by which point most people have made a full recovery. A small minority of people infected will end up with this problem and scientists are trying to find out, firstly, why this phenomenon occurs, but also why it only affects some people and not others. Vishvajyth Ponnambalam explores the effect of studies into serotonin on our understanding of Long Covid …
Serotonin has commonly been linked to diseases such as epilepsy, major depressive disorder (MDD) and migraines
One interesting theory that has recently been put forward is that low serotonin levels (the ‘happy hormone’) can explain the phenomena. Serotonin is a neurotransmitter which is made in the body from the amino acid tryptophan in the gut, which is acquired from our diet. The reduction of this amino acid can lead to a decrease in serotonin which in turn affects certain functions in our brain. Serotonin is involved in mood regulation, sleep and cognition, among others, so it is vital to our regular functioning. It has commonly been linked to diseases such as epilepsy, major depressive disorder (MDD) and migraines.
A research team at the University of Pennsylvania Perelman School of Medicine, who published this study in the Cell, injected mice with either a Covid-19 strain found in Long Covid Patients or a drug which causes an inflammatory response in the blood, which then caused the decrease in blood serotonin levels. The low blood serotonin levels were also observed in patients being treated in hospital for the respiratory disease. This similarity forms the basis of their conclusions.
The scientific literature therefore strongly suggests that serotonin is indeed linked to Covid – 19
Another study in 2022 from Denmark found that serotonin was depleted because tryptophan’s metabolism was dysregulated. They based their findings on research that during the acute phase of Covid-19 infection, tryptophan metabolism was disrupted. The scientific literature therefore strongly suggests that serotonin is indeed linked to Covid – 19. But is it the root cause of Long Covid?
But there has not been major evidence so far to corroborate the study from Pennsylvania, and discussions within the scientific community have raised important questions about its legitimacy. For one, the experiment was conducted on mice, not humans, highlighting the lack of concrete proof that the phenomenon can be applied to us too. The serotonin levels in the brain were also not affected, which would still leave the question as to how certain side effects such as fatigue occurs.
On the flip side, if this study has hit the nail on the head and low levels of serotonin does indeed lead to Long covid, how does this impact our understanding? Well, perhaps those who are experiencing or have experienced depressive episodes may be more likely to experience Long Covid., as these patients will already have low serotonin. Drugs such as Selective Serotonin Reuptake Inhibitors (SSRIs) which are commonly prescribed for depression could also be suggested to help with patients suffering from Long Covid, which the team at Pennsylvania hope to do. The 2022 study has also found that SSRIs do indeed help in the resolution of symptoms, so it is likely that these will be their next steps.
longer studies can also be conducted, observing the long-term effects, which was not possible a few years ago
Regardless, I find this study very interesting and it could be a possible explanation for Long Covid. It’s important to keep trying to find answers in order to help prevent further casualties and improve current treatment plans, and this study inspired the wannabe scientist in me to look more deeply into this subject. For instance, brain fog, which is the term commonly used to describe the cognitive and memory symptoms of Covid-19 is especially associated with Long Covid, but how does this occur if brain serotonin levels are stable? Perhaps future research should be more focused on this aspect. As more time passes, longer studies can also be conducted, observing the long-term effects, which was not possible a few years ago. But as it usually is with biology and the human body, there may be other factors at play that affect how some people are more susceptible to getting Long Covid. Who knows, perhaps this research could help bring us one step closer to finally unravelling the mystery of Long Covid?
Vishvajyth Ponnambalam
Featured image courtesy of Fusion Medical Animation via Unsplash. Image license found here.
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