From Ergo Log
Take a daily 700 mg L-cystine and 280 mg L-theanine and you'll reduce your chance of catching cold by seventy percent. Researchers at Ajinomoto, Japan came to this conclusion after doing an experiment on 173 people.
We also wrote about the immune-modulatory effect of the cysteine-theanine combination back in 2010. A human study that showed that supplementation with these two amino acids helped strength athletes to keep their immune system in shape when doing intensive training. This is probably because L-theanine and L-cystine are building blocks of the detoxifying molecule glutathione [structural formula shown below].
To be more precise: glutathione is a tripeptide in cells that need detoxifying enzymes in order to be able to do their work. Glutathione consists of glutamine, theanine and cysteine. Cystine is a dipeptide of two cysteine molecules. Quite how it works the researchers don't know, but the immune system functions better the more glutathione the cells have available.
In 2007 researchers in Ajinomoto published the results of an animal study in which L-theanine and L-cystine supplementation in mice in a ratio of 2:5 after they had been given a vaccination boosted the production of antibodies. [J Vet Med Sci. 2007 Dec; 69(12): 1263-70.]
When researchers at Nagoya Kosein Hospital looked whether more elderly humans also reacted better to flu vaccinations after receiving supplements containing the two amino acids they indeed saw a positive effect – but only in the people who had a low-protein diet. Geriatr Gerontol Int. 2008 Dec;8(4): 243-50.]
According to animal studies done at the Osaka Prefectural Institute of Public Health, the combination of L-theanine and L-cystine protects older mice against flu viruses [J Vet Med Sci. 2010 Feb; 72(2): 157-65.] In the publication this article is about the Ajinomoto researchers examined whether the combo had a similar effect on human adults.
The researchers gave half of their subjects a placebo and the other half were given pills containing L-cystine and L-theanine. The subjects had to take their doses after breakfast and after lunch, and administration continued for five weeks. The figure and table below show that there were considerably fewer incidences of the common cold in the group that took the combination than in the control group.
"The results of the present exploratory trial showed that L-theanine & L-cystine is an effective and safe drug as a food ingredient to suppress the common cold, and we anticipate its use as a drug or food ingredient for cold prevention and symptom relief in the future", the researchers write.
J Amino Acids. 2010; 2010:307475.