Green Tea, Black Tea, and Tea Extracts: Science and Safety


Ingredient suppliers are increasingly advancing tea compounds outside of the cup.

As many tea drinkers will tell you, drinking cup after cup will likely send you scurrying to the washroom. For those wishing to relax their bladders and free up the time required to brew and consume tea, ingredient suppliers are increasingly advancing tea compounds outside of the cup. From green tea to its fermented self in black tea, tea (Camellia sinensis) remains a strong presence on America’s dietary supplement shelves.

Weight Management

If one consumes enough green tea or green tea extract, human and animal studies imply that a reduction in body fat can occur.(1–4) While the mechanism for this effect isn’t entirely certain, it likely has to do with increased energy expenditure and/or reducing the body’s absorption of fat.(5)

Further support of a weight-loss effect may come from tea’s potential influence on cholesterol. A tea extract meta-analysis conducted this August dissected 14 randomized controlled trials of over 1100 subjects, ultimately linking green tea intake to significant reductions in mean total cholesterol (7.2 mg/dL) and mean low-density lipoprotein (LDL) cholesterol (2.19 mg/dL).(6)

Data tracking for the cholesterol meta-analysis came from studies on dosages ranging from 150 to 2500 mg/day of green tea catechins (polyphenols credited with tea’s weight-loss benefits). Inconsistent dosing levels represent just one caveat humbly noted by green tea researchers in their quest for knowledge, time and time again. Population studies can also be conflicted by caffeinated tea intake, where caffeine’s potential effect on weight loss may blur the weight-loss effect of catechins. Some research suggests that high-caffeine consumers will see less of a weight aid from green tea-maybe even increased cholesterol(7)-yet caffeine, traditionally considered a thermogenic ingredient within industry, has demonstrated a potential to oxidize fat.(8)

However you look at it, available science consistently points to a high intake of tea/tea extract as needed for health impacts. As University of Oxford researcher Navamayooran Thavanesan explains in a recent green tea and weight-loss review, “As many studies have inadvertently demonstrated, the intake of polyphenols seems to require a reasonably high dosage, often translating to five or more cups a day…”(9)

Heart Disease

Numerous population studies on tea intake have focused on a link to reduced heart disease risk, likely due to a range of potential mechanisms, including the weight-loss factors referenced above. A 2010 review on population-based tea studies declared that existing reviews “strongly suggest a decreased risk of CVD with higher tea consumption. The available data also suggest that the magnitude of the benefit of green and black tea is similar.” The review cites improved health factors such as reduced risk of ischemic stroke, total mortality, and reduced risk of heart disease.(10)

Improvements in endothelial function also appear to be associated with high tea intake.


Epigallocatechin gallate (EGCG), an abundant polyphenol in tea, is known to induce cell death (apoptosis) in precancerous or cancer cells, which should inhibit tumor development or progression.(11) The theory that tea consumption may reduce cancer risk stems from research on EGCG, tea’s overall antioxidant profile, and even a notion that tea compounds might induce apoptosis via pro-oxidant effects.

Yet proof of a benefit of tea consumption on cancer prevention is “sparse and very inconsistent,” as Cochrane researcher Katja Boehm put it in her team’s 2009 review of green tea consumption and cancer.(12)

Forced to rely almost entirely on observational studies, Boehm’s team determined that prostate cancer showed the most potential for a reduced risk of cancer in those who consume higher amounts of green tea.

Recent breast cancer meta-analyses bode well for green tea, too, but not black tea(13)-a determination that could be based as much on the limited access to black tea studies globally as to the chemical differences between black and green tea.

Relaxation and Focus

L-theanine is an amino acid found naturally in tea and, with few exceptions, nowhere else. It is believed to provide much of tea’s taste.

A prevailing scientific theory has it that tea can produce feelings of calmness-not from its toasty temperature but, rather, from L-theanine. Supplementation with this amino acid has demonstrated reduced stress responses (e.g., heart rate) after a stress-inducing task,(14) reduced blood pressure, and increased production of gamma amino butyric acid (GABA), which releases serotonin and dopamine.(15)

Scientists further suggest that there is relaxed alertness associated with L-theanine intake, as trials point to resulting increases in the brain’s production of alpha waves, brain waves produced during awake, yet relaxed, states. In a 2008 study, 35 subjects were instructed to rest their eyes while hooked up to electroencephalograph recording. The recording detected significant changes in alpha wave production from 50 mg of L-theanine supplementation compared to placebo.(16)

Mental focus might be further supported by a combination of L-theanine and caffeine, as evidenced by several recent cognitive task studies where reaction timing and attention to tasks were improved with the two ingredients over placebo.(17–19) L-theanine may even dumb down the unwanted jitters that come with caffeine intake, as one 2000 rat study suggests.(20)

Scientific consensus has suggested that maximum concentration of L-theanine reaches the bloodstream in 30 minutes to 2 hours, so there is potential for use as a daily stress-management routine.

Just how much L-theanine is needed to experience significant changes? Not enough from just one cup of tea, according to Takami Kakuda of Japanese tea product developer Ito En Ltd. (Tokyo). Kakuda says that published trials suggest the beneficial effects are “...observed with daily consumption of pure L-theanine of at least 50 mg, an amount equivalent to a minimum of three cups of tea. Furthermore, many of these studies were done using between 150 and 250 mg L-theanine, doses which would not be easily achieved even by the most avid tea drinkers…”(21)


Can too much consumption of tea extract pose a health risk? Concern relating to overconsumption of tea extract has been significant in the scientific field, so let’s turn to one of the more recent assessments.

Axel H. Schönthal of the University of Southern California Keck School of Medicine took up a review of green tea extract pharmacokinetic and safety studies, published in the April 2011 issue of Molecular Nutrition & Food Research.(22) Looking at eight major studies dating as far back as 1998, evidence of clear adverse health effects appears slim. “Altogether, all studies with human subjects showed that purified EGCG, [green tea extract], or polyphenon E, equivalent to the EGCG content of 8 to 16 cups of green tea, were safe and well tolerated,” writes Schönthal.

One popularly discussed outlier is liver damage. Some studies have linked intake of green tea extract (alone or in combination with other ingredients) as toxic to the liver, but this is contrasted by numerous studies that assessed liver damage risk and concluded there was none.

But Schönthal’s review does make mention of the United States Pharmacopeia (USP), an organization in charge of setting food standards internationally, which conducted its own review of green tea extract safety in 2008. The committee retrieved 34 case reports of liver issues with green tea extract deemed either “possible causality” or “probable causality.” In its report, published in the journal Drug Safety, USP proposed to assign a Class 2 safety warning for decaffeinated green tea extracts.(23) Had it passed, the Class 2 warning would have required a label on most green tea extract product, alerting consumers and healthcare professionals of potential health risks. Following additional review and acceptance of stakeholder comments, the committee deferred approval of a labeling requirement.(24)

Black Tea

Hidden amongst all of the research focusing on green tea is that on black tea, the fermented form of green tea retaining a somewhat similar table of compounds. Due in part to observational studies focusing mostly on green tea, research on black tea is dwarfed by that of green tea, yet research stands in support of black tea for many of the same benefits.

Where black tea differs is in its natural thearubigins, compounds generated during the fermentation process. Early in vitro research on thearubigins hints at a potential for cancer risk reduction,(25) yet the fermentation process that creates thearubigins is also believed to reduce available levels of tea catechins.(26)

Suppliers’ Standardized Tea Ingredients
  • Indena (MILAN, ITALY): Indena offers GreenSelect and GreenSelect Phytosome green tea extracts. With over 25 reported years of engagement in green tea research, the company has determined that complexing its green tea with phospholipids is optimal for catechin bioavailability; hence the marketing of GreenSelect Phytosome. Published studies conducted by Indena support its ingredients for weight loss, antioxidant defenses, and increased EGCG bioavailability with the phospholipid carrier.
  • Stratum Nutrition (St. Charles, Mo): TeaFense is a combination of green tea and capsicum intended to provide increased catechin bioavailability. Based on the common notion that Asian populations have a reduced risk of heart disease, the company is taking it one step further, alleging that Asian populations with diets centered around green tea and peppers demonstrate even further reduced heart-disease risk. TeaFense is also standardized for EGCG.
  • Kemin Health (Des Moines, IA): Kemin’s Assuritea line includes Assuritea Green, a green tea extract, and Assuritea Wellbeing, a hybrid of carefully selected black and green tea extracts. Both products are standardized for a holistic increase of a range of green tea catechins.
  • Javaplant (Jakarta Barat, Indonesia): The company offers a BTX black tea powder extract.
  • Blue California (Rancho Santa Margarita, CA): The company’s L-TeaActive L-theanine ingredient was deemed Generally Recognized as Safe (GRAS) for foods and beverages in 2010.
  • Ethical Naturals (San Anselmo, CA): AlphaWave is Ethical Naturals’ GRAS-affirmed L-theanine ingredient produced from L-pyroglutamic acid. Along with extracts standardized for EGCG, the company also offers a “calming blend” of L-theanine with chamomile, valerian, hops, and other botanicals.




1. R Hursel et al., "The effects of green tea on weight loss and weight maintenance: a meta-analysis," International Journal of Obesity, vol. 33, no. 9 (September 2009): 956–961.

2. H Wang et al., "Effects of catechin enriched green tea on body composition," Obesity, vol. 18, no. 4 (April 2010): 773–779.

3. A Basu et al., "Green tea supplementation affects body weight, lipids, and lipid peroxidation in obese subjects with metabolic syndrome," Journal of the American College of Nutrition, vol. 29, no. 1 (February 2010): 31–40.

4. S Sae-Tan et al., "Weight control and prevention of metabolic syndrome by green tea," Pharmacological Research, vol. 64, no. 2 (August 2011): 146–154.

5. N Thavanesan, “The putative effects of green tea on body fat: an evaluation of the evidence and a review of the potential mechanisms,” British Journal of Nutrition, published online August 3, 2011.

6. Zheng et al., “Green tea intake lowers fasting serum total and LDL cholesterol in adults: a meta-analysis of 14 randomized controlled trials,” American Journal of Clinical Nutrition, vol. 94, no. 2 (August 2011): 601–610.

7. K Kempf et al., “Effects of coffee consumption on subclinical inflammation and other risk factors for type 2 diabetes: a clinical trial,” American Journal of Clinical Nutrition, vol. 91, no. 4 (April 2010): 950–957.

8. TM Rains et al., “Antiobesity effects of green tea catechins: a mechanistic review,” Journal of Nutritional Biochemistry, vol. 22, no. 1 (January 2011): 1–7.

9. N Thavanesan, “The putative effects of green tea on body fat: an evaluation of the evidence and a review of the potential mechanisms,” British Journal of Nutrition, published online August 3, 2011.

10. JM Hodgson et al., "Tea flavanoids and cardiovascular health," Molecular Aspects of Medicine, vol. 31, no. 6 (December 2010): 495–502.

11. BN Singh et al., “Green tea catechin, epigallocatechin-3-gallate (EGCG): mechanisms, perspectives, and clinical applications,” Biochemical Pharmacology, published online July 30, 2011.

12. K Boehm et al., "Green tea (Camellia sinensis) for the prevention of cancer," The Cochrane Library, published online July 8, 2009.

13. P Zhou et al., “Green tea consumption and breast cancer risk: three recent meta-analyses,” Breast Cancer Research and Treatment, vol. 127, no. 2 (June 2011): 581–583.

14. K Kimura et al., “L-theanine reduces psychological and physiological stress responses,” Biological Psychology, vol. 74, no. 1 (January 2007): 39–45.

15. Q Vuong et al., “L-theanine: properties, synthesis, and isolation from tea,” Journal of the Science of Food and Agriculture, vol. 91, no. 11 (August 2011): 1931–1939.

16. AC Nobre et al., “L-theanine, a natural constituent of tea, and its effects on mental state,” Asia Pacific Journal of Clinical Nutrition, vol. 17, supp. 1 (2008): 167–168.

17. CF Haskell et al., “The effects of L-theanine, caffeine, and their combination on cognition and mood,” Biological Psychology, vol. 77, no. 2 (February 2008): 113–122.

18.  GN Owen et al., “The combined effects of L-theanine and caffeine on cognitive performance and mood,” Nutritional Neuroscience, vol. 11, no. 4 (August 2008): 193–198.

19. SJ Einöther et al., “L-theanine and caffeine improve task switching but not intersensory attention or subjective alertness,” Appetite, vol. 54, no. 2 (April 2010): 406–409.

20. T. Kakuda et al.,"Inhibiting effects of theanineon caffeinestimulation evaluated by EEG in the rat, Bioscience, Biotechnology, and Biochemistry, vol. 64, no. 2 (February 2000), pp. 287–293.

21. T Terashima et al., “Time-dependent changes of amino acids in the serum, liver, brain, and urine of rats administered with theanine,” Bioscience, Biotechnology, and Biochemistry, vol. 63, no. 4 (1999): 615–618.

22. AH Schönthal, "Adverse effects of concentrated green tea extracts," Molecular Nutrition & Food Research, vol. 55, no. 6 (June 2011): 874–885.

23. DN Sarma et al., "Safety of green tea extracts: a systematic review by the US Pharmacopeia," Drug Safety, vol. 31, no. 6 (2008): 469–484.

24. U.S. Pharmacopeia, "USP to defer decision on green tea extract cautionary labeling," news release, June 23, 2008.

25. U Bhattacharya et al., "Comparative antimutagenic and anticancer activity of three fractions of black tea ployphenols thearubigins," Nutrition and Cancer, vol. 63, no. 7 (October 2011): 1122–1132.

26. FM Ngure et al., "Catechins depletion patterns in relation to theaflavin and thearubigins formation," Food Chemistry, vol. 115, no. 1 (July 2009): 8–14.

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