Investigating the Role of Serotonin Levels in Cognitive Impairments Associated with Long COVID-19

This study aimed to investigate the activation of the inflammation process, triggered as an immune response to combat the invasion by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). SARS-CoV-2 is a highly transmissible and pathogenic coronavirus that emerged in late 2019 and has caused a pandemic of acute respiratory disease, named 'coronavirus disease 2019' (COVID-19). Several mechanisms contribute to the reduction in serotonin levels, such as the impaired absorption of dietary tryptophan, hindered serotonin transport via platelets, and increased activity of an enzyme responsible for breaking down serotonin. Individuals seeking treatment for long COVID-19 had lower serotonin levels in their blood than those who had fully recovered from the infection. Furthermore, patients with long COVID-19 also had reduced tryptophan levels. The potential benefits of dietary supplementation with tryptophan or the use of selective serotonin reuptake inhibitors (SSRIs) to improve cognitive impairments and depressive and anxiety disorders in long-term COVID-19 patients. The findings support the immune response's pivotal role in modulating serotonin levels and further highlight the intricate connection between the immune system and neurotransmitter regulation.