L-theanine is an amino acid like no other. Most amino acids form the building blocks of proteins, but L-theanine stands alone. It occurs naturally in both black and green tea, dissolves easily in water and can cross the blood-brain barrier, so it can affect brain activity. But it does so much more than that.

L-theanine can:

• Help prevent cancers forming and growing.

• Reduce nausea and vomiting during chemo.

• Speed up healing and recovery after cancer surgery.

• Decrease chemo-related neuropathy.

• Improve brain function.

• Help to improve immune function.

• Lower stress.

Pretty impressive, isn't it? Let's look at these in more depth.

L-theanine's Anti-cancer Effects

L-theanine helps to maintain healthy levels of glutathione in the body. Glutathione is the master antioxidant, so L-theanine can protect the body from oxidative stress, which is a major source of inflammation, a risk factor for cancer (1).

Glutathione is also crucial for detoxifying carcinogens in the body, further enhancing its protective effect (2).

During chemo, high levels of glutathione in the tumour cells are associated with tumour growth and resistance to chemo because glutathione increases the rate at which the tumour cells can remove the drugs. L-theanine helps by reducing that removal and improving the effects of the treatment (2), while the higher levels of glutathione in the surrounding healthy cells protect them from the damaging effects of the drugs (1).

L-Theanine Mitigates the Adverse Events of Chemotherapy

One of the miserable side effects of chemo is how it affects the digestive system, with nausea, vomiting and diarrhoea being common problems. It can become so severe that doctors pause or stop treatment.

S-1 is an oral chemotherapy drug combination that is often used in gastrointestinal cancer patients. It often causes diarrhoea and nausea so badly that doctors interrupt treatment. In a randomised controlled trial, patients on S-1 therapy also received a combination of L-theanine and cystine, another amino acid. The patients had fewer and less severe side effects, especially diarrhoea. The researchers attributed it to increased glutathione levels in the healthy cells (3).

L-Theanine and Its Benefits After Cancer Surgery

Because of L-theanine's anti-inflammatory effects, researchers conducted trials on patients who had undergone surgery to see whether it would help to reduce recovery time.

In the first trial, the patients underwent esophagectomy, which is the removal of the oesophagus. This operation often leads to significant inflammation, which can slow recovery. One group of patients received a mixture of cystine and L-theanine starting 3 days before surgery and continuing until 7 days after it, while the other group took a placebo. The supplemented group had significantly lower levels of pro-inflammatory markers. They had fewer post-surgical complications, such as leakage from the two ends of the reconstructed channel (anastomotic leakage), and there weren't as many cases of pneumonia as in the placebo group. Their hospital stays were shorter and recovery was faster too (4).

The second trial involved a group of patients undergoing removal of part of the stomach for gastric cancer. Again, one group received a mixture of cystine (700 mg) and theanine (280 mg) for 10 days starting 4 days before their surgery, whilst the other group took a placebo. As in the first trial, the supplemented group had reduced levels of pro-inflammatory markers. They also had a lower resting energy expenditure, which suggested a lower stress response (5).

L-Theanine's Impact on Chemotherapy-Induced Neuropathy

Oxaliplatin is a commonly used chemotherapy drug that's used to treat a range of different cancers, including colorectal cancer. One of the common side-effects of its use is peripheral neuropathy. It's very unpleasant and can be severe enough to cause doctors to stop or pause treatment.

Peripheral neuropathy happens because of damage to the nerves in the hands, feet, arms or legs, usually the sensory nerves. It can sometimes also affect the motor nerves that control movement and the autonomic nerves that control things like sweating, balance and digestion that we don't think about. The most common symptoms are:

• numbness

• tingling

• pain

• pins and needles

• aching, cramps and weakness

• a burning sensation.

A group of colorectal cancer patients being treated with oxaliplatin was divided into two cohorts. One took daily doses of cystine (700 mg) and theanine (280 mg), whilst the other received a placebo. The treatment group experienced significantly less neuropathy (6).

Enhancing Cognitive Function with L-Theanine

One of the best-known benefits of L-theanine is its ability to improve cognitive function and help with relaxation.

L-theanine inhibits glutamate, which is a neurotransmitter that stimulates the nervous system, and increases levels of dopamine, GABA and serotonin levels in the brain, which are all calming neurotransmitters.

It also stimulates the brain to produce alpha waves, as measured on an electroencephalogram (EEG). Alpha waves are associated with an alert but relaxed state, such as during non-REM sleep and meditation, but they don't cause drowsiness.

A group of patients with mild cognitive impairment was divided into 2 groups. One took a combination of 1440 mg of green tea extract and 240 mg of L-theanine daily for 16 weeks, whilst the other received a placebo. The treatment group showed significant improvements in memory scores, delayed recall and selective attention (7).

In another trial, researchers injected a group of mice with amyloid proteins from Alzheimer's patients, effectively inducing Alzheimer's in them. The researchers then fed half of the mice water with L-theanine in it, while the other half had plain water. After 5 weeks, the treatment group performed better on memory tests. After dissecting their brains, the researchers found less evidence of nerve cell death and oxidative damage in the treatment group too. There were also higher levels of glutathione, the body's main antioxidant, suggesting that the L-theanine had increased antioxidant production (8).

To date, there aren't any studies on the effects of L-theanine on cancer patients to see whether it would help with the brain fog that many of us suffer from, commonly called chemo brain. But the studies above suggest that it would be probably be useful.

Boosting Immune Function with L-Theanine

Researchers have known for some time that supplementation with glutathione improves immune function, and also that cystine and L-theanine are precursors for glutathione, as we discussed when we were talking about L-theanine's effects on the digestive issues experienced by chemo patients.

After successful tests on immunised mice to see how they responded to vaccination after taking cystine and L-theanine (9), a human trial tested the same combination to see whether the treatments twice daily for 35 days reduced the number of cold and flu symptoms. They conducted the trial in Japan during their peak season for flu. They found that there was a much lower incidence of colds and flu symptoms compared with the placebo group (10).

Three healthcare facilities were the setting for a similar trial on older adults in Japan, again during the peak flu season, to see whether a combination of green tea extract and theanine could protect the healthcare workers from the flu. Most of them had received the influenza vaccine. The results showed a significant reduction in the incidence of flu compared to the placebo group (11).

It's difficult to tell whether these results would translate to the immune systems of cancer patients. If you're receiving immunotherapy, L-theanine could be helpful for boosting its effects, although there aren't any studies on this yet. But if you have completed your treatment and are having vaccinations against flu, COVID or any other virus, L-theanine might help to boost your immune system to get a better response from the vaccine.

The Anti-Stress Effects of L-Theanine

Stress is probably the most widely experienced side effect of a cancer diagnosis. And it's a difficult one to deal with, so any safe supplement is worth trying.

In a placebo-controlled trial, a group of moderately stressed participants took a mental arithmetic test before and after receiving either 200 mg of L-theanine or a placebo. After 7 days, the groups were then reversed, so that the original placebo group took the L-theanine and vice versa. The results showed that each time the L-theanine group experienced a calming effect, with reduced blood pressure, salivary cortisol and heart rate, their EEGs showing an increase in alpha brain wave activity, and a questionnaire revealing that they felt more relaxed (12).

Improving Sleep Quality with L-Theanine

Sleep is another area that is badly affected by both a cancer diagnosis. Stress is partly to blame, and many of the drugs used in treatment affect sleep quality too. And from personal experience, it can take a long time to improve too.

L-Theanine alone will relax you, but it doesn't make you drowsy. However, scientists used a combination of 700 mg of GABA and 200 mg of L-theanine daily on a group of adults with sleep problems for 4 weeks in an exploratory study to see whether they would improve sleep quality. They completed a questionnaire to measure their subjective feelings about their sleep, but also used a wearable device to measure their sleep quality. The questionnaire showed a significant improvement, and the device detected improvements too, especially in sleep recovery and in lowering heart rate whilst they were sleeping (13).

Although there haven't been any studies involving cancer patients yet, it could be a useful addition to your arsenal.

Dosage and safety of L-theanine

L-theanine works quickly, with maximum effects felt about 30-50 minutes after taking it, and its effects last for about 3-5 hours, with most of it being removed from the body within 24 hours. A small amount remains in red blood cells after that (14).

It's classified as safe, even for children, although the longest studies are 6 weeks for children and 8 weeks for adults. There isn't any information on whether it's safe during pregnancy or breastfeeding, so avoid using it then (15).

It can lower blood pressure, so if you're taking medication to reduce blood pressure, L-theanine could increase its effects (15).

The usual dose is 200 mg once or twice daily.

Conclusion

L-theanine is an excellent supplement for cancer patients. It's safe and effective for coping with various issues.

There are other supplements and herbs that you might find equally helpful for the same problems. I cover them in my book. Watch the video in the link to find out more about the book, and you can find all your local online stores that stock it by clicking on the button below.

References

1. Reynolds B. L-Theanine: The calming neutraliser. FX Medicine. September 15, 2015. Accessed June 25, 2024. https://www.fxmedicine.com.au/blog-post/l-theanine-calming-neutraliser.

2. Kennedy L, Sandhu JK, Harper M-E, Cuperlovic-Culf M. Role of glutathione in cancer: From mechanisms to therapies. Biomolecules. 2020;10(10):1429. doi:10.3390/biom10101429

3. Tsuchiya T, Honda H, Oikawa M, et al. Oral administration of the amino acids cystine and theanine attenuates the adverse events of S-1 adjuvant chemotherapy in gastrointestinal cancer patients. International Journal of Clinical Oncology. 2016;21(6):1085-1090. doi:10.1007/s10147-016-0996-7

4. Okamoto H, Taniyama Y, Sakurai T, et al. Perioperative administration of cystine and theanine suppresses inflammation and facilitates early rehabilitation and recovery after esophagectomy: A randomized, double-blind, controlled clinical trial. Nutrients. 2022;14(11):2319. doi:10.3390/nu14112319

5. Miyachi T, Tsuchiya T, Oyama A, et al. Perioperative oral administration of Cystine and theanine enhances recovery after distal gastrectomy. Journal of Parenteral and Enteral Nutrition. 2012;37(3):384-391. doi:10.1177/0148607112458798

6. Kobayashi M, Sato R, Komura T, et al. Protective effect of the oral administration of Cystine and theanine on Oxaliplatin-induced peripheral neuropathy: A pilot randomized trial. International Journal of Clinical Oncology. 2020;25(10):1814-1821. doi:10.1007/s10147-020-01728-4

7. Park SK, Jung I, Lee WK, et al. Combination effect of green tea extract and L-theanine on memory and attention in mild cognitive impaired subjects: A randomized double-blind placebo-controlled study. Proceedings of the Nutrition Society. 2010;69(OCE6):E518. doi:10.1017/s0029665110003812

8. Mobbs A. Is L-theanine a natural nootropic? Intelligent Labs. September 6, 2021. Accessed June 27, 2024. https://www.intelligentlabs.org/l-theanine-benefits/.

9. Kurihara S, Shibahara S, Arisaka H, Akiyama Y. Enhancement of antigen-specific immunoglobulin G production in mice by co-administration of L-cystine and L-Theanine. Journal of Veterinary Medical Science. 2007;69(12):1263-1270. doi:10.1292/jvms.69.1263

10. Kurihara S, Hiraoka T, Akutsu M, Sukegawa E, Bannai M, Shibahara S. Effects of L-cystine and L-theanine supplementation on the common cold: A randomized, double-blind, and placebo-controlled trial. Journal of Amino Acids. 2010;2010(Article ID 307475):1-7. doi:10.4061/2010/307475

11. Matsumoto K, Yamada H, Takuma N, Niino H, Sagesaka YM. Effects of green tea catechins and theanine on preventing influenza infection among healthcare workers: A randomized controlled trial - BMC Complementary Medicine and therapies. BioMed Central. February 21, 2011. Accessed June 28, 2024. http://www.biomedcentral.com/1472-6882/11/15.

12. Evans M, McDonald AC, Xiong L, Crowley DC, Guthrie N. A randomized, triple-blind, placebo-controlled, crossover study to investigate the efficacy of a single dose of AlphaWave® L-theanine on stress in a healthy adult population. Neurology and Therapy. 2021;10(2):1061-1078. doi:10.1007/s40120-021-00284-x

13. Konno H, Murotani R, Kamada Y. An exploratory study to detect the effects of the combined intake of gamma-aminobutyric acid (GABA) and L-theanine on sleep by wearable device. Published online October 3, 2023. doi:10.1101/2023.10.01.23296182

14. Scheid L, Ellinger S, Alteheld B, et al. Kinetics of ʟ-theanine uptake and metabolism in healthy participants are comparable after ingestion of ʟ-theanine via capsules and green tea. The Journal of Nutrition. 2012;142(12):2091-2096. doi:10.3945/jn.112.166371

15. Natural Medicines Database. Theanine. NatMed Pro - Login. June 9, 2023. Accessed July 1, 2024. https://naturalmedicines.therapeuticresearch.com/databases/food,-herbs-supplements/professional.aspx?productid=1053.