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.