Serotonin drops during long COVID, could help in early detection

Scientists believe that deciphering the mystery of long COVID requires early detection of the condition — possible through certain identifiable biomarkers. Several new studies have documented these biological changes that accompany long COVID, and one such study says that serotonin might be one of the key elements to look for.

Explainer: In their study published this Monday, researchers at the University of Pennsylvania suggest that the inflammation that occurred due to COVID-19 causes a drop in serotonin — a neurotransmitter involved in mood, memory, and digestion.

• Blood analysis of 58 long COVID patients was compared to 60 individuals with an acute coronavirus infection and 30 people with no post-COVID symptoms.
• The more long COVID symptoms patients had, the lower their serotonin levels, the study found.
• In addition, some patients still had some viral remnants in their stool samples, indicating reservoirs in the gut of some individuals long after infection.
• The researchers suggest that persistent viral inflammation causes the depletion of serotonin — which could explain the cognitive and neurological symptoms of long COVID, like memory problems and brain fog.

Few previous studies have already suggested a link between serotonin levels and the post-acute sequelae of SARS-CoV-2 (PASC) infection.

Here’s what the researchers believe is happening: Viruses can linger in our bodies for months or years after initial infection. These viral remnants left behind can trigger persistent inflammation. This reduces the body’s ability to absorb tryptophan — a precursor of serotonin.

The study concludes that long COVID depletes “peripheral” serotonin, which circulates throughout the body and not just the brain. Along with memory, this interferes with the activity of the vagus nerve — the nerve that regulates digestion, respiratory rate, and heart rate.

Why it matters: PASC is an area of ongoing investigation, where a limitation in diagnosis makes it hard to link suffering individuals to long COVID.

• Despite some common signs, long COVID symptoms can be nonspecific, while others might experience no symptoms at all.
• Long COVID detection requires effective tools — biomarkers that can be identified through blood tests in a general clinical setting.
• This data shows the places we should be looking at. While not everyone shows low serotonin levels, it can be an important marker in long COVID diagnosis — along with abnormal immune cell levels and reduced levels of cortisol.
• “I don’t think there’s at this point any changes in terms of testing that needs to be done for the individual patient or treatment that are going to be effective for long COVID,” said Benjamin Abramoff, director of Penn Medicine’s Post-COVID Assessment and Recovery Clinic and a co-author of the study. “But I think there’s new promising insight” that will lead to “beneficial therapeutics down the road,” he added.

Serotonin levels can be restored through supplementation with tryptophan or the use of selective serotonin reuptake inhibitors (SSRIs), animal studies showed.

Some researchers are looking to start a clinical trial that uses fluoxetine — an SSRI commonly marketed as Prozac — for the treatment of long COVID, noted the NY Times.