IngredientsBotanical name: Camellia sinensis (L.) O. Kuntze, family Theaceae. The common name "oolong" is a transliteration of the Chinese wĆ«lĂłng (çéŸ), meaning "black dragon." Oolong tea has its roots in the Qing dynasty, originating in China's Fujian mountainous regions.
Processing status and taxonomy among teas: Tea is classified into six fermentation categories: green tea (non-fermented), yellow tea (microfermented), white tea (slightly fermented), oolong tea (semi-fermented), black tea (fully fermented), and dark tea (post-fermented). Oolong tea is categorized as a semi-fermented tea. For tea, "fermentation" refers to the natural browning reactions induced by oxidative enzymes in the cells of tea leaves. Because of this intermediate processing, it is slightly oxidized, and hence the taste and aroma lies somewhat between green and black tea; some types taste more like green tea while others taste more like black tea, depending on the degree of oxidation during processing.
Major named varieties: The most famous Chinese oolong teas include Tieguanyin, Dahongpao, Phoenix Narcissus, White Crest, Phoenix Bush, and Iron Lohan, while the most well-known Taiwanese oolongs include Dongding, Wenshan, Pouchong, and Oriental Beauty. These areas define the four major categories of oolong tea: Wu Yi Mountain Rock Oolong, Anxi Oolong, Guangdong Dan Cong, and Taiwan Oolong.
Common forms and preparations: Oolong is most commonly consumed as a brewed beverage prepared by steeping dried, partially oxidized tea leaves in hot water. It is also available as concentrated liquid extracts, powders, and encapsulated supplements. Less than 2% of tea manufactured in the world is semi-fermented oolong tea; however, due to the complex processing steps and the limited supply, oolong teas usually have a higher unit price than green or black teas in the international tea market.
Oolong tea has a long evolutionary history and is traced to the Tang Dynasty (618â907 CE) in the Beiyun region of Phoenix Mountain in Fujian Province. It was first known as Beiyun Tea and, because of its fine quality and unique flavor, attracted government officials, monks, and scholars who liked the "earth-stone" taste of the teas from the Wuyi Mountain region.
Fujian's tea makers, likely Buddhist monks operating in their temples, invented charcoal roasting techniques to dry their tea. The slow charcoal roasting coupled with the accidental oxidation of their tea defined the characteristic flavor of Wu Yi Shan's oolongs that continue to be produced today. Exactly when the process began is uncertain, though the first documented mention of this tea comes from a poem written by a monk living in Wu Yi Shan during the late Ming and early Qing Dynasties.
The fame of this tea spread to the Ming (1368â1644) and Qing (1644â1911) Dynasties. It was in the late 1725 that oolong tea was developed in the Anxi region of Fujian, and in 1796 oolong tea was introduced to northern Fujian and to Taiwan. In 1869, Taiwanese oolong tea was exported to the United States for the first time; it was a great success and quickly became popular in Europe and the rest of the world.
Traditional use attributed to oolong tea a wide range of health functions in Chinese medicine and folk practice, including body weight management, anti-obesity and hypolipidemic effects, and general vigor. According to traditional Chinese belief, oolong tea is effective in the control of body weight, though few controlled studies had been conducted historically to measure its actual impact on energy expenditure.
Gongfu tea ceremony: In China and Taiwan, oolong tea symbolizes hospitality, respect, and social harmony, and is used in ceremonies such as weddings and business meetings. In the Gongfu (Kung Fu) tea tradition, which originated in Fujian and Guangdong and later spread to Taiwan, oolong teasâparticularly Wuyi Rock oolong and Tieguanyinâare prepared in small Yixing clay teapots using multiple short infusions with near-boiling water. This method is designed to extract different aromatic and flavor compounds across successive steepings and is considered both a ritual art and a mark of hospitality.
Tieguanyin lore: Anxi county's Tieguanyin ("Iron Goddess of Mercy") is one of China's most internationally recognized teas, with its own origin legend: a poor farmer named Wei Yin (or, in an alternate version, Wang Shi Rang in the 18th century) discovered a special tea plant growing near a derelict Guanyin temple and cultivated it with devotion. The tea eventually came to the attention of the Qing court and became a tribute tea.
Oolong tea contains catechins, theaflavins, and thearubigins, as well as some characteristic components: epigallocatechin esters, dimeric catechins (such as theasinensins), and dimeric proanthocyanidins. The composition and content of 24 tea constituents have been analyzed in tea, including catechins, flavonol and flavone glycosides, phenolic acids, and purine alkaloids.
Theaflavins and thearubigins are major polyphenolic compounds in black tea, whereas theasinensins are the most characteristic for oolong tea. Theasinensins are dimeric catechins formed during the partial oxidation of the tea leaf and are largely absent from both unoxidized green tea and fully oxidized black tea, making them biochemically distinctive to oolong.
The flavonols mainly exist in the form of O-glycosides, while the dominant aglycones of flavonol glycosides in oolong tea are quercetin, kaempferol, and myricetin. Phenolic acids, including hydroxybenzoic acids and hydroxycinnamic acids, are also commonly found in free and bound forms in tea.
When commercial teas are analyzed by HPLC, the levels of (â)-epigallocatechin 3-gallate (EGCG) and total catechins in teas are in the order: green tea (old leaves) > green tea (young leaves) and oolong tea > black tea and pu-erh tea. In comparison with green tea, oolong tea contains approximately half the caffeine and epigallocatechin gallate, while polymerized polyphenols are approximately double.
Tea catechins are strong antioxidants that scavenge free radicals and prevent the formation of reactive oxygen species (ROS) by chelating metal ions. Among tea catechins, EGCG has the strongest antioxidant activity and has been studied extensively.
Analysis of oolong tea by high-performance liquid chromatography and mass spectrometry identified the major catechins and two methylxanthines, caffeine and theophylline, as well as other constituents. In a study in which 37 commercial white, green, oolong, black, and pu-erh tea samples were quantified by HPLC-diode array detection, the mean L-theanine content of oolong tea was 6.09 mg/g, and the caffeine content was 19.31 mg/g.
L-Theanine (Îł-glutamylethylamide) is an amino acid characteristic of Camellia sinensis. Oolong tea contains more theanine and catechins than fresh young tea, and levels of theanine, EGC, and EGCG in young leaves rise markedly with the withering process. Caffeine, a methylxanthine, antagonizes adenosine receptors and exhibits a synergistic effect with L-theanine, resulting in a state of calmness and reduced mental fatigue.
Abundant volatile compounds, such as alcohols, aldehydes, hydrocarbons, and ketones, are associated with the aroma of oolong tea. Key aroma-active compounds identified in Dongding, Tieguanyin, and Dahongpao oolongs include 2-methylpropanal, 3-methylbutanal, nerolidol, (E)-2-heptenal, hexanal, octanal, ÎČ-damascenone, indole, 6-methyl-5-hepten-2-one, (R)-(â)-linalool, and dimethyl sulfide. Floral monoterpenes, including linalool, linalool oxide II, and geraniol, are consistently higher in high-altitude teas, consistent with the sensory finding of stronger floral intensity in high-altitude samples.
Many of the main taste compounds in oolong tea, such as 2 alkaloids, 11 flavan-3-ols, 8 organic acids and esters, and 3 theaflavins, have been identified by HPLC combined with UV spectrophotometry and mass spectrometry. Oolong tea polysaccharides represent an additional class of bioactive macromolecule studied in relation to metabolic effects.
Tea catechins are strong antioxidants that scavenge free radicals and prevent the formation of reactive oxygen species by chelating metal ions. The in vivo antioxidant activities of tea polyphenols cannot be simply extrapolated from their in vitro antioxidant effects due to differences in bioavailability.
With varying degrees of fermentation, tea undergoes complex chemical transformations resulting in the formation of unique compounds such as thearubigins, theaflavins, and theasinensins. Theaflavins and theasinensins, in particular, have been reported to exhibit anti-inflammatory effects in several studies. Oolong tea-derived theasinensins also attenuated COX-2 expression in a dose-dependent manner in activated murine macrophages.
Laboratory and clinical reports converge on mechanisms by which oolong polyphenolsâcatechins, theasinensins, and related compoundsâcould improve glycemic control, including competitive inhibition of carbohydrate-digesting enzymes like α-amylase and modulation of insulin sensitivity and inflammatory pathways. The mechanism of antihyperglycemic activities of theasinensin A and B was found to be promotion of glucose transporter 4 (GLUT4) translocation to the plasma membrane to increase glucose intake in rat skeletal muscle cells (L6 myotubes) through the CaMKK/AMPK signaling pathway, but not through the PI3K/Akt pathway.
In animal research, oolong tea prevented obesity and fatty liver induced by a high-fat diet, and a water extract of oolong tea enhanced noradrenaline-induced lipolysis, with caffeine identified as the active substance. Oolong tea's polymerized polyphenols have also been suggested to increase energy expenditure independently of caffeine.
Scientific evidence suggests that oolong tea extracts have antibacterial activity against Streptococcus mutans and Streptococcus sabrinus, and that oolong tea rich in epigallocatechin gallate showed antimicrobial activity against Candida species. Theasinensin A was found to effectively suppress the oxacillin resistance of methicillin-resistant Staphylococcus aureus (MRSA), with decreased viable MRSA cells and reduced minimum inhibitory concentration (MIC) of oxacillin; the effect lasted about 10 hours.
A randomized crossover design study compared 24-hour energy expenditure (EE) in 12 men consuming either water, full-strength oolong tea (brewed from 15 g of tea daily), half-strength tea (brewed from 7.5 g), or caffeinated water. Relative to the water treatment, EE was significantly increased by 2.9% for full-strength tea and 3.4% for caffeinated water. This increase represented an additional expenditure of 281 kJ/d and 331 kJ/d respectively. In addition, fat oxidation was significantly higher (12%) when subjects consumed the full-strength tea rather than water.
Oolong tea is a traditional Chinese tea long believed to decrease body fat. A crossover study evaluated the effect of oolong tea on energy expenditure (EE) in comparison with green tea. The subjects were eleven healthy Japanese females (mean age 20 ± 1 y; BMI 21.2 ± 2.5 kg/mÂČ) who consumed three treatments: water, oolong tea, or green tea. Resting energy expenditure and EE after consumption of the test beverage for 120 minutes were measured using an indirect calorimeter. In comparison with green tea, oolong tea contained approximately half the caffeine and EGCG, while polymerized polyphenols were double. These results suggest that oolong tea increases EE by its polymerized polyphenols.
In one earlier study, 102 Chinese women who drank four cups of oolong tea per day (the brew from four 2-g tea bags) lost over a kilogram of body weight during a six-week period.
In animal models, eight weeks of oolong tea supplementation with 93.94% polyphenols significantly decreased body weight gain, adipose tissue mass, and serum levels of triglyceride (2.60 mmol/L), cholesterol (5.49 mmol/L), and low-density lipoprotein cholesterol (0.61 mmol/L) in high-fat diet-fed mice. Oolong tea intervention also improved fat accumulation, hepatic damage, glucose intolerance, and endotoxemia, and alleviated inflammation by decreasing levels of pro-inflammatory factors.
Evidence strength: Evidence for acute increases in energy expenditure in humans is supported by small controlled crossover studies. Long-term weight-loss evidence in humans is limited to small trials with methodological limitations (small sample sizes, short durations, open-label design, or single populations). Animal data are consistent but cannot be directly extrapolated to humans. Overall, evidence is preliminary to moderate.
A prospective randomized crossover study investigated whether oolong tea influences plasma adiponectin levels, LDL particle size, total cholesterol, HDL and LDL cholesterol, serum triglyceride, and plasma glucose in patients with coronary artery disease (CAD). Twenty-two patients consumed oolong tea (1,000 ml) or water for 1 month. There was a significant difference in plasma adiponectin levels before and after one month of oolong tea intake (6.26 ± 3.26 ”g/ml versus 6.88 ± 3.28 ”g/ml, P < 0.05), and in plasma LDL particle size (25.02 ± 0.67 nm versus 25.31 ± 0.60 nm, P < 0.01).
A significant difference in hemoglobin A1c levels was also observed (7.23 ± 4.45% versus 6.99 ± 4.30%, P < 0.05) before and after oolong tea intake, and the authors concluded oolong tea may have beneficial effects on the progression of atherosclerosis in patients with CAD.
The intake of oolong tea has been associated with preventing obesity and improving lipid metabolism, demonstrated by an ability to lower total cholesterol and plasma triglyceride levels, along with reductions in blood pressure and platelet aggregation activity.
Available epidemiological studies suggest favorable effects of green, oolong, and black tea, with benefit from modest to extremely high amounts of tea consumption. However, a number of difficulties make it extraordinarily difficult to conduct randomized clinical trials with tea, and it remains unclear what type and dose to recommend or study.
Three cups of tea per day, including black, green, and oolong varieties, have been associated with a 24% decrease in ischemic stroke and a 13% decrease in total stroke in some observational analyses.
Evidence strength: Cardiovascular evidence is largely observational and epidemiological, supplemented by small clinical trials. The 22-patient crossover CAD study is encouraging but limited in size and lacks blinding. Epidemiological stroke data cannot establish causation. Evidence is preliminary.
Hosoda and colleagues observed that consumption of oolong tea (1,500 ml/day) for 30 days in a placebo-controlled crossover study lowered fasting glucose in 20 patients with type 2 diabetes mellitus on hypoglycemic drugs.
In contrast, a double-blind crossover study was conducted in which healthy males (n = 19) consumed each of three oolong tea products or a control beverage as part of a controlled diet. Neither oolong tea nor oolong tea supplemented with catechins or other polyphenols produced improved glucose metabolism in healthy adult volunteers.
Several large studies have investigated the relationship between tea consumption and the risk of developing diabetes mellitus, yielding mixed results. While some studies have reported a significant reduction in diabetes risk associated with tea consumption, others have found neutral effects.
Evidence strength: Effects appear to be population-specific: positive signals in patients with established type 2 diabetes; no demonstrated benefit in non-diabetic adults. The evidence base consists of small, often short-duration trials. Overall evidence is mixed and insufficient to draw definitive conclusions.
Study results in animal models demonstrated that administration of tea (green, black, or oolong) has suppressed type I and type IV allergic reactions. To test the effectiveness of oolong tea in the treatment of recalcitrant atopic dermatitis, 121 patients were enrolled; 118 completed the open study. Participants, while continuing their usual medications, were instructed to consume oolong tea daily (10 g steeped in 1,000 mL water per day, divided into three doses). Positive outcomes were observed within 1 to 2 weeks, with 63% of participants showing improvement. A good response to treatment was still observed in 54% at 6 months.
The dermatologists attributed the therapeutic effectiveness to the anti-allergic properties of tea polyphenols.
Evidence strength: The 2001 Uehara et al. open-label study published in Archives of Dermatology is the primary clinical reference. It is an open (non-blinded) study without a placebo control arm, which limits the ability to exclude placebo effect and concurrent standard-treatment confounding. Evidence is preliminary but notable given the study size (n = 118) and durability of response at 6 months.
A study analyzed the relationship between oolong tea drinking and bone mineral density in postmenopausal Han Chinese women while controlling for living and dietary habits, fertility, disease elements, and other baseline conditions. One group included 124 cases who routinely drank oolong tea, and the other included 556 who did not drink tea. Four or more cups of tea per day have been connected to an increase in bone mineral density across the body, while 2 to 3 cups per day are linked to improved bone mineral density in the spine, attributed to the antioxidant content of tea.
Note: A 2014 study by Wang et al. on oolong tea and bone loss in postmenopausal women was subsequently retracted (PMID 28526908). This retraction is documented in PubMed.
Evidence strength: Observational and population-based data suggest an association, but causality has not been established via controlled trials. Evidence is preliminary, and at least one retracted study in this area warrants caution.
Scientific evidence suggests that oolong tea extracts have antibacterial activity against Streptococcus mutans and Streptococcus sabrinus. Oolong tea rich in EGCG showed antimicrobial activity against Candida species. Several studies with tea polyphenols showed that antimicrobial activity was related to: (1) galloylated catechins agitating the structural features of bacterial cellular membranes to impair microbial cell walls; (2) EGCG inhibiting penicillinase, an enzyme that degrades penicillin; and (3) EGCG potentially injuring bacteria through a pro-oxidative action.
Evidence strength: Evidence is predominantly in vitro. Human clinical trials for dental health endpoints specifically with oolong tea are limited.
Oolong tea, partially fermented from Camellia sinensis leaves, exhibits significant antioxidative, anti-inflammatory, and anti-cancer activities as indicated in several in vitro and in vivo studies. Induction of apoptosis by theasinensin A is important for the cancer chemopreventive function of oolong tea. Oolong tea also exhibits stronger antimutagenic effects than green or black tea, with polyphenols inhibiting cancer cell invasion, inducing apoptosis, and causing cell cycle arrest. Notably, oolong tea's anti-inflammatory activity reportedly surpasses that of green and black teas; its catechins, tannins, and theaflavins, formed during partial fermentation, are considered key to these effects due to their role in reducing oxidative damage and cancer-promoting inflammation.
Evidence strength: Although oolong tea exhibits significant antioxidative, anti-inflammatory, and anti-cancer activities in several in vitro and in vivo studies, studies on health-promoting effects of oolong tea and its characteristic compounds are limited. Human clinical trial data for cancer prevention or treatment are essentially absent. Evidence is preclinical only (in vitro and animal models).
The bioactive components of oolong tea cannot be absorbed in the small intestine because of their limited bioavailability, so it is speculated that most beneficial ingredients reach the large intestine where they can be metabolized by gut microbes and modulate host metabolisms. Alleviation of oolong tea on high-fat diet-induced obesity in animal models may be partially attributed to the modulation of gut microbiota composition.
Evidence strength: Gut microbiota data are primarily from rodent models. Human evidence is limited and indirect. Evidence is preliminary.
The following dosages are reported as used in specific published studies. They do not represent recommended clinical doses.
Several clinically important cautions are documented: oolong contains caffeine, which can raise heart rate, provoke arrhythmias in susceptible people, and alter insulin responses after glucose loads. Taking oolong tea along with stimulant drugs might cause serious problems including increased heart rate and high blood pressure.
Drinking tea can interfere with iron absorption, which can lead to iron deficiency anemia. This effect is attributed to the polyphenolic tannins in tea chelating non-heme iron in the gastrointestinal tract, reducing its bioavailability.
Oolong tea contains caffeine. Caffeine is reported to have antiplatelet activity. Theoretically, the caffeine in oolong tea might increase the risk of bleeding when used concomitantly with anticoagulant or antiplatelet agents. However, this interaction has not been reported in humans. Tea polyphenols and extracts have been reported to reduce platelet aggregation, and separately caffeine may slow blood clottingâtogether these findings imply potential additive bleeding risk for patients on anticoagulants or antiplatelet drugs.
A published case report describes a male who experienced several transient ischemic attack-like symptoms immediately following consumption of a cup of high-quality oolong tea. A thorough medical evaluation uncovered no evidence of a true TIA. The patient was a 72-year-old male with hypertension and atrial fibrillation taking valsartan/hydrochlorothiazide and warfarin. While causality was not established, the report underscores the need for caution in patients on anticoagulant therapy.
Oolong tea should not be consumed simultaneously with other stimulants such as amphetamines or ephedrine, as doing so could cause serious heart problems.
Pregnant women should limit themselves to no more than three cups of tea a day, since excess caffeine can cause problems such as premature birth and low birth weight.
High-dose catechins (EGCG) have been linked to gastrointestinal and neurological symptoms and rare allergic sensitization, so concentrated supplementsâas opposed to brewed teaâcarry the greater risk.
Tea (green, oolong, and black) is the second most widely consumed beverage worldwide, second only to water, and aside from a few reported adverse effects, tea appears to be broadly safe for human consumption. Evidence is mixed and limited: randomized trials in non-diabetic adults found no glucose benefit, and safety concerns including caffeine effects, EGCG side effects, and effects on clotting mean oolong should be considered an adjunct rather than a substitute for prescribed drugs.
Health conditions that Oolong tea may help support.
Body systems that Oolong tea may help support.
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