TRYPTOPHAN

What is tryptophan?

Tryptophan is an amino acid we must obtain from our diet [^[1]].

What does tryptophan do in the body?

Our bodies use tryptophan to make serotonin, a chemical used as a neurotransmitter in the brain and the gut. Tryptophan is also required to make melatonin, a hormone related to the sleep-wake cycle. When one doesn’t get enough niacin to meet the body’s metabolic requirements or the amount of tryptophan consumed exceeds what is needed for protein synthesis, tryptophan is used to make the cofactor NAD+ [^[2]].

How can tryptophan help alleviate certain Long COVID symptoms and pathophysiology? 

Long COVID is linked to lowered serotonin levels, which the body makes from tryptophan [^[3]]. Reduced serotonin can impair cognition, which can cause Long COVID cognitive problems such as “brain fog” and memory impairments [^[4]]. Therefore, tryptophan supplementation may improve cognitive ability as it can restore serotonin levels. Serotonin is also found in the gut, where viral components of SARS-CoV-2, which causes COVID-19, can linger after acute COVID-19 infection. Therefore, there may be a connection between tryptophan and serotonin’s actions in the gut, where there may be a lingering virus in the gastrointestinal tract and persistence of Long COVID symptoms in individuals [^[5]].

Lowered tryptophan levels can also contribute to inflammation in both acute and Long COVID [^[6]]. Severe COVID-19 is associated with tryptophan depletion [^[7]]. One study looking at tryptophan in Long COVID found that decreased oxygen saturation in acute COVID-19, which partially explained the variance in serum tryptophan, predicts Long COVID anxiety [^[8]]. Researchers believe altered tryptophan absorption and metabolism could be a main contributor to Long COVID [^[9]].