Boosting Vaccine Effectiveness!
To establish this effect in people, researchers designed a randomized, placebo-controlled study in which both of these amino acids were tested in healthy elderly humans. For the study, 65 nursing home residents aged 65 or over were randomly divided into two groups. The test group received 280 milligrams of L-theanine and 700 milligrams of L-cystine once a day for 14 days. The other group received a placebo for the same amount of time.19
On day 15, all participants were given a flu vaccine containing three influenza strains.
The scientists found that certain subsets of the L-theanine and L-cystine group had an increased rate of seroconversion, the precise point at which the immune system develops antibody protection against a microorganism as a result of immunization. Notably, the increased seroconversion rate occurred among subjects with low serum total protein or hemoglobin, potential indicators of compromised health.19
The report concluded that, “Co-administration of L-cystine and L-theanine before vaccination may enhance the immune response to influenza vaccine in elderly subjects with low serum total protein or hemoglobin.”
In another human study, this same combination has been shown to reduce the incidence of the common cold by 58%.5
Reduce the Risk of Common Cold
If co-administration of these two amino acids could boost the effectiveness of the flu vaccine, scientists reasoned that it might also help lower the incidence of the common cold.
The common cold is the most prevalent human illness.5 The majority of cases are acute viral infections of the upper respiratory tract. Conventional treatments such as analgesic agents and antihistamines only help alleviate some of the symptoms, such as sneezing and runny nose.5
Because common colds can lead to serious complications in elderly and immune-compromised individuals,21 scientists set out to determine if L-theanine and L-cystine, could also reduce the incidence of the common cold.
For the placebo-controlled study, 176 healthy men were asked to take a total of 700 milligrams of L-cystine and 280 milligrams L-theanine per day, in two divided doses.5
Over a five-week period, the L-theanine and L-cystine group developed 58% fewer colds than the placebo group.5 Among those experiencing colds, the symptoms of fever and chills were significantly reduced in the theanine/cystine supplemented group.5
The study team reported that, together, L-theanine and L-cystine represent an effective and safe natural ingredient to suppress the common cold—producing no more side effects than placebo.5