1 Introduction
COVID-19 is an infectious disease caused by the SARS-CoV-2 virus.[1]
The treatment has not been established and vaccine development is
delayed. Internationally, the number of SARS-CoV-2-infected patients
exceeds 25,000,000. In Japan, ≥70,000 persons have been infected and the
number of patients is increasing.[2]
According to a review of patients who died in Japan, persons aged ≥70
years accounted for 80%. The overall mortality rate is 1.6%, but it
increases with age. It is ≤1% in those aged 10 to 49 years, whereas the
rates in those aged 60 to 69 years, 70 to 79 years, and 80 to 89 years
are 1.9, 5.7, and 11.5%, respectively; the mortality rate in elderly
persons is reportedly ≥10-times higher than in young persons.[3] As
immune deficiency is noted in the elderly, it is important to prevent
immune deficiency and improve the immunity in the current situation in
which treatment has not been established.
Cystine is synthesized through bimolecular binding of cysteine, as a
sulfur-containing amino acid, to disulfide. It is contained in many
foodstuffs, including meat. After cellular uptake, cystine is reduced to
cysteine. Theanine is a tea component, and is decomposed to glutamic
acid and ethylamide after being absorbed in vivo. Intracellular
cysteine, glutamic acid, and glycine function as substrates for the
synthesis of glutathione, which exhibits the most potent antioxidant
actions in vivo.[4]
A previous study reported that the simultaneous administration of
cystine and theanine (C/T) stimulated influenza antigen-specific
immunoglobulin G (IgG) antibody production via glutathione synthesis in
mice. An experiment using old mice also yielded similar
results.[5-6] Furthermore, a study involving humans reported that
C/T administration significantly increased antibody production after
influenza vaccination in elderly patients with malnutrition.[7]
These findings suggest that C/T administration influences the clinical
course of SARS-CoV-2 virus infection. We report 4 SARS-CoV-2-infected
patients who were admitted to our hospital, and treated using a
supplement containing cystine (700 mg) and theanine (280 mg), leading to
favorable results.