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L-theanine amino acid to boost effectiveness of flu vaccination

Enhanced Winter Wellness Against Colds & Flu

Every year, over 30,000 people die from the flu. Even more alarming is the fact that most individuals over 64 are not protected against the most virulent forms of the flu even though they receive an annual vaccine shot. New evidence shows that the amino acids L-theanine and L-cystine boost flu vaccine effectiveness in certain elderly groups and protect all groups studied against winter colds.

Scientifically reviewed by Dr. Gary Gonzalez, MD, in May 2022. Written by: Michael Downey, Health & Wellness Author.

Enhanced Winter Wellness Against Colds & Flu

It’s one of the top 10 killers in the US, causing an average estimate of over 30,000 people to die each year.1,2 It’s not heart disease or cancer or diabetes… it’s the flu.

Most people associate the flu with muscle pain, coughing, sore throat, fatigue, and other symptoms, but the flu can turn into a deadly infection.2,3

Scientists have found two ingredients that prime the immune system to defend against the onslaught of influenza and other seasonal pathogens that can result in serious illness and even death.2,4,5

The Deadly Complications of Influenza

If you think of the flu as merely a seasonal risk or inconvenience, think again. Although known for uncomfortable symptoms such as sore throat, nasal discharge, chills, fever, muscle pain, headaches, coughing, nausea, and fatigue3,6—the harsh reality is that tens of thousands of Americans die from influenza infection in an average year.

Potentially lethal results of the flu can include either direct viral pneumonia or secondary bacterial pneumonia,7,8 and complications of chronic conditions such as congestive heart failure and chronic obstructive pulmonary disease (COPD).9

Almost 90% of all American deaths caused by influenza are among those over 65 years old.10 One reason is the immune senescence suffered by virtually all aging individuals. Vaccines function by eliciting an antibody response against specific viruses . The ability to generate an antibody response to influenza vaccines is severely compromised in the elderly.11

But the elderly are not the only ones at risk of flu-related death. High-risk groups also include pregnant women, the immunocompromised, children under age two, and people who have chronic illnesses such as asthma, diabetes, heart disease.12

Shocking Flu Statistics
Shocking Flu Statistics

On average, influenza is estimated to cause over 30,000 deaths in the United States annually.1

The antibody response of elderly patients to influenza vaccine has been shown to be blunted.11

Complications of viral influenza infection may involve several organ systems.22

Flu shots fail to protect older persons from the most virulent strains up to 91% of the time.18

The flu vaccine’s effectiveness among the general population is only about 56%.18

Flu-related deaths for persons over age 85 are 16 times greater than that of slightly younger persons aged 65-69.23

Flu infection is estimated to cause more than 200,000 hospitalizations annually in the United States.22

Chronic medical conditions—such as heart disease, lung disease, diabetes, kidney disease, liver disease, dementia, and stroke—are all risk factors for potentially lethal influenza complications.12

The most frequent serious flu complications are pulmonary, such as primary influenza pneumonia, secondary bacterial pneumonia, or chronic pulmonary diseases.7-9

Influenza A caused by H5N1 virus (“avian flu”) often infects young, previously healthy persons—with a fatality rate of about 60%, usually due to respiratory failure.24

Neurologic complications of influenza, such as encephalopathy, are most common in children.25

Increased rates of schizophrenia were noted in offspring of women who had the flu in the second pregnancy trimester, implying fetal developmental brain effects.26

Abnormal cardiac findings were found in 43% of adult flu patients,suggesting influenza pneumonia may predispose patients to serious cardiac complications such as myocarditis and pericarditis.27

The Best Defense Against the Flu

Receiving an annual flu shot is an effort many individuals, particularly those over age 65, make in an attempt to prevent both influenza infection and its deadly outcomes.13 The reason is that it mobilizes what is known as adaptive or acquired immunity.14 After the body has been “primed” with specific, non-infective viruses in the form of a vaccine, the immune system can then make antibodies to protect against future infection with these viruses.14

However, for a flu vaccine to even begin to protect against the influenza virus contained within it, the vaccinated individual must first have sound immune function—so that the immune system can properly respond to stimulation by the vaccine’s antigen.15

The trouble is that, in those with weakened immunity—such as the elderly population—vaccine stimulation triggers only a limited antibody response, thus limiting the effectiveness of the vaccine.16,17

That means, despite being vaccinated, aging individuals remain highly susceptible to infection. This can be one reason why up to 91% of those 65 and over who get a flu shot may still be susceptible to getting the flu!18

But there’s good news. Scientists have recently found a way to boost the effectiveness of the flu vaccine. Exciting new evidence shows that, taken together for two weeks prior to vaccination, the amino acids L-theanine and L-cystine enhance the efficacy of the flu vaccine in certain subsets of elderly subjects.19 This delivers strong protection against the flu virus—and its deadly complications.

These two compounds do not enhance the vaccine itself; instead, they help boost the immune system’s acquired immune response, giving your body the tools it needs to effectively utilize the vaccine.19

Better Together

When these complementary amino acids were used together in animal studies, they increased immune response.4,20

In one study, researchers gave both L-theanine and L-cystine orally to mice for 10 days. Six days after infection with influenza, the treated mice had lower lung concentrations of the virus. Ten days after infection, there was a significant enhancement of key anti-influenza-virus antibodies (called immunoglobulin G or IgG).4

Scientists realized that the co-administration of L-cystine and L-theanine could restore age-related impairment of immune competence, helping to prevent influenza and other viral infections—and in turn, preventing deadly complications.4

Based on this knowledge, scientists set out to determine if these two substances could boost vaccine effectiveness by targeting (and enhancing) the immune system itself.

What You Need to Know
Boosting Vaccine Effectiveness

Boosting Vaccine Effectiveness

  • On average each year, it is estimated that over 30,000 Americans die from influenza.
  • The recommended annual flu shot protects older Americans from a virulent strain as infrequently as 9% of the time and protects the general population only 56% of the time. One of the reasons is that in the elderly, who are far more likely to have generalized weakened immunity, vaccine stimulation triggers only a limited antibody response.
  • Taken together for two weeks prior to vaccination, the amino acids L-theanine and L-cystine enhance efficacy of the flu vaccine in a subset of elderly subjects. This delivers stronger protection against both the flu virus—and its deadly complications.
  • Remarkably, this same combination has been shown to reduce the incidence of the common cold by 58%.

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

The Aging Immune System
The Aging Immune System

A compromised immune system can present an opportunity for a simple bout of the flu to quickly progress to full-blown pneumonia, which is the eighth leading cause of death for Americans.2

Nutritional deficiencies among the elderly can lower immune defenses.28 For instance, deficiency of iron, vitamin B12, or folate is a common cause of the increased incidence of anemia in the elderly, and this in turn is associated with a greater risk of infectious diseases.5 In fact, malnutrition at any age causes a decline in immune function and increased susceptibility to infection.5,28-30

Further compounding the problem, millions of doctors erroneously prescribe antibiotics to patients seeking relief for symptoms of viral infections. Persistent misuse of antibiotics leads to potentially serious treatment complications, greater risk of death, and may contribute to the development of antibiotic-resistant pathogens.31

As numerous strains of influenza viruses continue to evolve and pose a deadly danger of complications to aging individuals, scientists recognized the urgent need to find a safe and effective way to reverse the reduced effectiveness of flu vaccines caused by age-related immune decline.

If taken together for two weeks prior to vaccination, the amino acids L-theanine and L-cystine enhance efficacy of the flu vaccine in certain groups of elderly subjects.19 This delivers stronger protection against both the flu virus—and its deadly complications.

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

Priming the Immune System
Priming the Immune System

In order for any vaccine to effectively do its job, it needs to work hand-in-hand with a healthy immune system. Studies have shown that the older you are, the less effective the flu vaccine becomes. This is a direct result of an age-related decline in immune response.

The amino acids L-theanine and L-cystine are known for their ability to boost factors of the immune system that are diminished with age: glutathione and interleukin-2.19,32,33

Glutathione is the major antioxidant that neutralizes free radicals and reactive oxygen compounds and is essential for the immune system to exert its full potential.19

Interleukin-2 is a cytokine that is important for antibody production and for the differentiation, long-term growth, and proper functioning of T cells.18,34

L-theanine, an amino acid and phytochemical found mainly in tea leaves (Camellia sinensis), is an immune booster.35,36 Theanine is known to stimulate glutathione.19 Theanine and glutathione have been shown to promote a certain subset of white blood cells known as gamma delta T lymphocytes that play a vital role in the production of interleukin-2.18,36 Evidence indicates that a greater intake of L-theanine helps to prime gamma delta T cells, activating them to a state of readiness.36,37

L-theanine also enhances the immune system by stimulating the release of immune system proteins called cytokines.19,36

L-theanine also contributes to the absorption of another amino acid important to the immune responsiveness: L-cystine.19 The amino acid L-cystine is a precursor to the antioxidant glutathione. L-cystine is converted to glutathione, which stimulates gamma delta T-cells to release the immune factor interleukin-2.19


The flu can mean more than symptoms such as muscle pain, nausea, and sore throat.3 On average, over 30,000 Americans die annually from influenza.1

To help prevent death from the flu’s lethal secondary infections and other complications, many people choose to receive an annual flu shot.13 However, because older adults often have a weakened immune system, the vaccine may only be effective as infrequently as 9% of the time—and only 56% of the time in the general population.16-18

However, when taken together for two weeks prior to vaccination, the amino acids L-theanine and L-cystine boost the efficacy of the flu vaccine in certain elderly subjects by enhancing the immune system itself.19 The result is enhanced protection against both the flu virus—and its deadly complications.

Remarkably, this same combination has been shown to reduce the incidence of the common cold by 58%.5

If you have any questions on the scientific content of this article, please call a Life Extension® Health Advisor at 1-866-864-3027.


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