A surprising new reason of Long COVID

In a recent discovery, researchers have unveiled a potential key to understanding the lingering effects of COVID-19, commonly referred to as 'Long COVID.'The study published in Journal Cell has found that Long COVID (PASC) is associated with serotonin reduction, possibly explaining neurocognitive symptoms, providing insights for future therapeutic interventions.

Various hypotheses have been proposed to explain Long Covid, including viral persistence, chronic inflammation, hypercoagulability, and autonomic dysfunction, but a unifying explanation has been lacking. This latest research, conducted by a team of experts, suggests a possible common link between these hypotheses that could pave the way for therapeutic interventions. The central element identified is the reduction of serotonin in individuals suffering from Long COVID.

Serotonin, a neurotransmitter known for its role in mood regulation and various bodily functions, appears to be significantly reduced in patients with PASC. The study elucidates a series of mechanisms by which viral infection and type I interferon-driven inflammation contribute to this reduction. These mechanisms include diminished intestinal absorption of tryptophan, a serotonin precursor, as well as platelet hyperactivation and thrombocytopenia, which affect serotonin storage. Additionally, enhanced monoamine oxidase (MAO)-mediated serotonin turnover exacerbates the depletion of this crucial neurotransmitter.

One of the most significant findings is how this serotonin reduction impacts the nervous system. Peripheral serotonin reduction hinders the activity of the vagus nerve, a vital component of the autonomic nervous system, and consequently impairs hippocampal responses and memory function. This revelation provides a potential explanation for the neurocognitive symptoms experienced by individuals with Long COVID.

Reference: Wong et al., Serotonin reduction in post-acute sequelae of viral infection, Cell (2023), https://doi.org/10.1016/j.cell.2023.09.013