Figure 6.
Proposed mechanisms of phototherapy with full-spectrum light for the prevention and treatment of COVID-19. Phototherapy may induce (1) vitamin D3 biogenesis and (2) adiponectin, which are associated with both prevention and treatment of COVID-19 in terms of the reduction in COVID-19 risk factors (Figure 1). (3) The elevation of circulating alarmins and oxidative stress markers during inflammatory responses may be inhibited by phototherapy, partly through the induction of Nrf2-mediated antioxidant responses. (4) Gut dysbiosis (an elevated Firmicutes/Bacteroidetes ratio) may be modulated by phototherapy and may induce the beneficial bacteria Parabacteroides goldsteinii. (5) Phototherapy may reduce ACE2 expression, resulting in a reduced risk of virus (SARS-CoV-2) infection. For treatment, vitamin D3 may induce the ACE2/Ang-(1–7)/MasR axis and inhibit Ang-II-induced alarmin elevation, oxidative stress responses, and gut dysbiosis, which are associated with poor outcomes in COVID-19. ACE2: angiotensin-converting enzyme 2, Ang-(1–7): angiotensin 1–7, Ang-II: angiotensin II, AT1R: angiotensin type I receptor, MasR: Mas receptor, Nrf2: nuclear factor-erythroid 2-related factor 2.