Effects of -Cystine and -Theanine Supplementation on the Common Cold: A Randomized, Double-Blind, and Placebo-Controlled Trial

The common cold is one of the most frequent illnesses caused by viral infection. Recently, we have reported that oral administration of cystine and theanine (CT) to mice enhanced the humoral immune response associated with antibody production. Based on this mouse study, we investigated the effects of CT supplementation on the common cold in humans as a pilot study. A total of 176 healthy male volunteers were randomized to receive either placebo or CT (490？mg) tablets twice daily for 35 days. The incidence outcome was assessed using the definition in our laboratory based on questionnaires regarding cold symptoms. The incidence of subjects with colds during the trial was significantly lower in the CT group than in the placebo group, although the duration of the colds was not significantly different between the groups. These results suggest that CT supplementation may be useful for the prevention of the common cold. 1. Introduction The common cold, an acute infection properly known as “cold syndrome,” is the most common human illness. The majority of cases of cold syndrome are acute infections of the upper respiratory tract, and its major cause is viral infection. From 30 to 50% of cases of cold syndrome are caused by rhinoviruses, and 10 to 15% are caused by coronaviruses [1]. Conventional methods of treatment use medications, such as analgesic agents and antihistamines, but these are only effective for the alleviation of symptoms, such as sneezing and runny nose [2]. Furthermore, antiviral agents, such as neuraminidase inhibitors, are believed to be effective; however, their application is currently limited to the influenza virus [1, 3–6]. Recently, Chinese medicine and dietary supplements have attracted attention as effective new methods for the treatment and prevention of cold syndrome [7]; for example, vitamin C; allysine, which is found in garlic; and the extract of the natural herb Echinacea [8–10]. However, there have also been reports indicating that the incidence of cold syndrome is unaffected by the above treatments [11, 12], and thus their effectiveness has yet to be clearly demonstrated. In a previous experiment in mice, we revealed that the oral administration of and (CT) reinforced antigen-specific antibody production after antigen stimulation; these effects were possibly caused by the reinforcement of glutathione (GSH) synthesis and the humoral immune response [13]. Based on previous reports, the objective of this pilot study was to evaluate the effects of CT against cold syndrome in humans, using a double-blind comparative study. 2.